Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive...Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive properties was revealed. Bending deformation was applied to the microobjects based on the flexible spin valves in parallel to anisotropy axes. It was revealed that during the bend the magnetoresistance changes due to the joint impact of both the change of the magnetic field projection on the film plane and the change of the magnetic properties of the ferromagnetic layers. The obtained dependences have been used in construction of bending sensor, in which the flexible spin valve microstripes were united into the Wheatstone bridge.展开更多
A single-molecule magnet is a long-sought-after nanoscale component because it can enable us to miniaturize nonvolatile memory storage devices.The signature of a single-molecule magnet is switching between two bistabl...A single-molecule magnet is a long-sought-after nanoscale component because it can enable us to miniaturize nonvolatile memory storage devices.The signature of a single-molecule magnet is switching between two bistable magnetic ground states under an external magnetic field.Based on this feature,we theoretically investigate a magnetic-fieldcontrolled reversible resistance change active at low temperatures in a molecular magnetic tunnel junction,which consists of a single-molecule magnet sandwiched between a ferromagnetic electrode and a normal metal electrode.Our numerical results demonstrate that the molecular magnetism orientation can be manipulated by magnetic fields to be parallel/antiparallel to the ferromagnetic electrode magnetization.Moreover,different magnetic configurations can be“read out”based on different resistance states or different spin polarization parameters in the current spectrum,even in the absence of a magnetic field.Such an external magnetic field-controlled resistance state switching effect is similar to that in traditional spin valve devices.The difference between the two systems is that one of the ferromagnetic layers in the original device has been replaced by a magnetic molecule.This proposed scheme provides the possibility of better control of the spin freedom of electrons in molecular electrical devices,with potential applications in future high-density nonvolatile memory devices.展开更多
The magnetoresistance behavior and the magnetization reversal mode of NiFe/Cu/CoFe/IrMn spin valve giant magnetoresistance （SV-GMR） in nanoscale were investigated experimentally and theoretically by nanosized magnet...The magnetoresistance behavior and the magnetization reversal mode of NiFe/Cu/CoFe/IrMn spin valve giant magnetoresistance （SV-GMR） in nanoscale were investigated experimentally and theoretically by nanosized magnetic simulation methods. Based on the Landau-Lifshitz-Gilbert equation, a model with a special gridding was proposed to calculate the giant magnetoresistance ratio （MR） and investigate the magnetization reversal mode. The relationship between MR and the external magnetic field was obtained and analyzed. Studies into the variation of the magnetization distribution reveal that the magnetization reversal mode, that is, the jump variation mode for NiFe/Cu/CoFe/IrMn, depends greatly on the antiferromagnetic coupling behavior between the pinned layer and the antiferromagnetic layer. It is also found that the switching field is almost linear with the exchange coefficient.展开更多
We propose two possible spin valves based on a zigzag silicene nanoribbon（ZSR） ferromagnetic junction. By using the Landauer–B u¨tikker formula, we calculate the spin-resolved conductance spectrum of the syste...We propose two possible spin valves based on a zigzag silicene nanoribbon（ZSR） ferromagnetic junction. By using the Landauer–B u¨tikker formula, we calculate the spin-resolved conductance spectrum of the system and find that the spin transport is crucially dependent on the band structure of the ZSR tuned by a perpendicular electric field. When the ZSR is in the topological insulator phase under a zero electric field, the low-energy spin transport and its ON and OFF states in the tunneling junction mainly rely on the valley valve effect and the edge state of the energy band, which can be electrically modulated by the Fermi level, the spin–orbit coupling, and the local magnetization. When a nonzero perpendicular electric field is applied, the ZSR is a band insulator with a finite energy gap, the spin switch phenomenon is still preserved in the device and it does not come from the valley valve effect, but from the energy gap opened by the perpendicular electric field. The proposed device might be designed as electrical tunable spin valves to manipulate the spin degree of freedom of electrons in silicene.展开更多
A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm)is prepared by the high-vacuum direct current(DC)magnetron sputtering.The ...A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm)is prepared by the high-vacuum direct current(DC)magnetron sputtering.The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction(XRD),atomic force microscopy(AFM),and vibrating sample magnetometry.The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field.The results show that as the temperature increases,the IrMn(111)texture weakens,surface/interface roughness increases,and the exchange bias field decreases.Below 200℃,the exchange bias field decreases with the residence time increasing,and at the beginning of the negative saturation field,the exchange bias field Hex decreases first quickly and then slowly gradually.When the temperature is greater than 200℃,the exchange bias field is unchanged with the residence time increasing.展开更多
Top and bottom NiO-pinning spin valves of Si/Ta/NiO/Co/Cu/Co/Ta and Si/Ta/Co/Cu/Co/NiO/Ta were prepared by magnetron sputtering, and X-ray diffraction and giant magnetoresistance （GMR） ratio were measured in the tem...Top and bottom NiO-pinning spin valves of Si/Ta/NiO/Co/Cu/Co/Ta and Si/Ta/Co/Cu/Co/NiO/Ta were prepared by magnetron sputtering, and X-ray diffraction and giant magnetoresistance （GMR） ratio were measured in the temperature range from 5 to 300 K. For the bottom spin valve, the interracial roughness at NiO/Co is much smaller than that of Co/NiO in the top one. The Co/Cu and Cu/Co interfaces have the same roughness in the bottom and the top spin valves. NiO, Co, and Cu layers have （111） preferred orientations in the top one and random orientations in the bottom one. The GMR ratio of the bottom spin valve is larger than that of the top one at all temperatures and their difference increases with decreasing temperature.展开更多
The exchange-coupled [Co/Ni]N/Tb Fe nano-magnetic films can display strong perpendicular magnetic anisotropy(PMA) which depends on the Tb:Fe component ratio, Tb Fe layer thickness and the repetition number N of [Co/Ni...The exchange-coupled [Co/Ni]N/Tb Fe nano-magnetic films can display strong perpendicular magnetic anisotropy(PMA) which depends on the Tb:Fe component ratio, Tb Fe layer thickness and the repetition number N of [Co/Ni]Nmultilayer. Perpendicular spin valves in the nano thickness scale, consisting of a [Co/Ni]3free and a [Co/Ni]5/Tb Fe reference multilayer, show high giant magnetoresistance(GMR) signal of 6.5 % and a large switching field difference over3 k Oe. However, unexpected slanting of the free layer magnetization, accompanied by a reduced GMR ratio, was found to be caused by the presence of a thick Fe-rich or even a thin but Tb-rich Tb Fe layer. We attribute this phenomenon to the large magnetostriction effect of Tb Fe which probably induces strong stress acting on the free layer and hence reduces its interfacial PMA.展开更多
Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature.Clear spin accumulation signals are detected by the non-local measurement. By fitting the results...Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature.Clear spin accumulation signals are detected by the non-local measurement. By fitting the results to the one-dimensional diffusion equation,8.6% spin polarization of the Co/Ag interface and -180 nm spin diffusion length in Ag are obtained.Thermal treatment results show that the spin accumulation signal drastically decreases after 100℃ annealing, and disappears under 200℃ annealing. Our results demonstrate that, compared to the spin diffusion length, the decrease and the disappearance of the spin accumulation signal are mainly dominated by the variation of the interfacial spin polarization of the Co/Ag interface.展开更多
The extra heat generation in spin transport is usually interpreted in terms of the spin relaxation. Reformulating the heat generation rate, we find alternative current-force pairs without cross effects, which enable u...The extra heat generation in spin transport is usually interpreted in terms of the spin relaxation. Reformulating the heat generation rate, we find alternative current-force pairs without cross effects, which enable us to interpret the product of each pair as a distinct mechanism of heat generation. The results show that the spin-dependent part of the heat generation includes two terms. One is proportional to the square of the spin accumulation and arises from the spin relaxation. However, the other is proportional to the square of the spin-accumulation gradient and should be attributed to another mechanism, the spin diffusion. We illustrate the characteristics of the two mechanisms in a typical spin valve with a finite nonmagnetic spacer layer.展开更多
Interface engineering in device fabrication is a significant but complicated issue.Although great successes have been achieved by conventional physical in situ or ex situ methods,it still suffers from complicated proc...Interface engineering in device fabrication is a significant but complicated issue.Although great successes have been achieved by conventional physical in situ or ex situ methods,it still suffers from complicated procedures.In this work,we present a facile method for fabricating phthalocyanine(Pc)-based two-dimensional conductive metal–organic framework(MOF)films.Based on PcM-Cu(M=Ni,Cu,H_(2))MOF films,spin valves with a vertical configuration of La_(0.67)Sr_(0.33)MnO_(3)/PcM-Cu MOFs/Co were constructed successfully,and exhibited notably high negative magnetoresistance(MR)up to -22% at 50 K.The penetrated Co atoms coordinated with the dehydrogenated hydroxy groups in the MOFs resulting in an antiferromagnetic layer of the PcM-Cu-Co hybrid structure.Interestingly,a significant exchange bias effect was demonstrated at the PcM-Cu MOF/Co interface,beneficial for the MR behavior.Thus,our present study provides new insights into developing high-performance organic spin valves via de novo molecular design.展开更多
Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MT...Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MTJ devices has been proposed in two directions:improving device performance by utilizing advanced two-dimensional(2D)ferromagnetic materials or extending device functionalities by exploring the gate-tunable magnetic properties of ferromagnets.Based on the recent development of 2D magnets with the ease of external stimuli,such as electric field,due to their reduced dimensions,reliable prospects for gate-tunable MTJ devices can be achieved,shedding light on the great potential of next-generation MTJs with multiple functionalities for various application environments.While the electrical gate-tunable MTJ device is highly desirable for practical spintronic devices,it has not yet been demonstrated.Here,we demonstrate the experimental realization of a spin valve device by combining a vertical Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ with an electrolyte gate.The magnetoresistance ratio(MR ratio)of 36%for the intrinsic MTJ confirms the good performance of the device.By electrolyte gating,the tunneling MR ratio of Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ can be elevated 2.5 times,from 26%to 65%.Importantly,the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating,providing a promising method to control the magnetization configuration of the MTJ.Our work demonstrates a gate-tunable MTJ device toward the possibility for gate-controlled spintronic devices,paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.展开更多
Pseudo spin valves（SVs） exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers....Pseudo spin valves（SVs） exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt（5.0 nm）/[Co（0.4 nm）/Pt（0.6 nm）]3/Co（0.4 nm）/Cu（3.0 nm）and Cu（3.0 nm）/[Co（0.4 nm）/Pt（1.5 nm）]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity（HC） of both layers. The perpendicular giant magnetoresistance（GMR） of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.展开更多
Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to reali...Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to realize novel functionalities.Here,we report the fabrication of multi-state vertical spin valves without spacer layers by using vd W homo-junctions in which exfoliated Fe3GeTe2 nanoflakes act as ferromagnetic electrodes and/or interlayers.We demonstrate the typical behavior of two-state and threestate magnetoresistance for devices with two and three Fe3GeTe2 nanoflakes,respectively.Distinct from traditional spin valves with sandwich structures,our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices.Our work demonstrates the possibility of extend multi-state,non-volatile spin information to 2 D magnetic homo-junctions,and it emphasizes the utility of vd W interface as a fundamental building block for spintronic devices.展开更多
When spins are injected through graphene layers from a transition metal ferromagnet, high spin polarization can be achieved. When detected by another ferromagnet, the spin-polarized current makes high- and low-resista...When spins are injected through graphene layers from a transition metal ferromagnet, high spin polarization can be achieved. When detected by another ferromagnet, the spin-polarized current makes high- and low-resistance states in a ferromagnet/graphene/ferromagnet junction. Here, we report manifest spin valve effects from room temperature to 10 K in junctions comprising NiFe electrodes and an interlayer made of double-layer or single-layer graphene grown by chemical vapor deposition. We have found that the spin valve effect is stronger with double-layer graphene than with single-layer graphene. The ratio of relative magnetoresistance increases from 0.09% at room temperature to 0.14% at 10 K for single-layer graphene and from 0.27% at room temperature to 0.48% at 10 K for double-layer graphene. The spin valve effect is perceived to retain the spin-polarized transport in the vertical direction and the hysteretic nature of magnetoresistance provides the basic functionality of a memory device. We have also found that the junction resistance decreases monotonically as temperature is lowered and the current-voltage characteristics show linear behaviour. These results revealed that a graphene interlayer works not as a tunnel barrier but rather as a conducting thin film between two NiFe electrodes.展开更多
Organic spin valve (OSV), one of the most promising and representative devices involving spin injection, transport and detection, has drawn tremendous attention owing to their ultra-long spin relaxation time in the fi...Organic spin valve (OSV), one of the most promising and representative devices involving spin injection, transport and detection, has drawn tremendous attention owing to their ultra-long spin relaxation time in the field of molecular spintronics. Since the first demonstration of truly worked vertical OSV device in 2004, efforts in enhancement of high performance and pursuit of spin-related nature have been devoted in related field. It offers a new opportunity to develop the integrated flexible multi-functional arrays based on spintronics in the future. However, the unreliable working state in OSVs due to the lack of exploration on interface control will cause severe impact on the performance evaluation and further restrict their practical application. Herein, we focus on the recent progress in strategies for reliable fabrication and evaluation of typical OSVs in vertical configuration. Firstly, the challenges in protection of two spin interface properties and identification of spin-valve-like signals were proposed. Then, three points for attention including selection of bottom electrodes, optimization of organic spacer, and prevention of metal penetration to improve the device performance and reliability were mentioned. Particularly, various modified strategies to solve the “dead layer” issue were highlighted. Furthermore, we discussed the general protocols in the reliable evaluation of OSVs’ performance and transport mechanism identification. Notably, several key fundamentals resulting in spurious magnetoresistance (MR) response were illustrated. Finally, we also highlighted the future perspectives on spintronic devices of organic materials.展开更多
The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe_(3)O_(4)with drastic change in structure,conductivity a...The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe_(3)O_(4)with drastic change in structure,conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator.However,such modulating effect of Fe_(3)O_(4)in OSV has not been comprehensively investigated,especially below the Verwey transition temperature(Tv).Here,we highlight the important role of Fe_(3)O_(4)electrode in reliable-working and controllable Fe_(3)O_(4)/P3HT/Co polymer spin valves by investigating the magnetoresistance(MR)above and below 7V.In order to distinguish between different contributions to charge transport and related MR responses,the systematic electronic and magnetic characterizations were carried out in full temperature range.Particularly,the first-order metal-insulator transition in Fe_(3)O_(4)has a dramatic effect on the MR enhancement of polymer spin valves at 7V.Moreover,both the conducting mode transformation and MR line shape modulation could be accomplished across 7V.This research renders unique scenario to multimodal storage by external thermodynamic parameters,and further reveals the importance of spin-dependent interfacial modification in polymer spin valves.展开更多
Single crystals of organic semiconductors with perfect crystal structure and minimal density of defects can exhibit high mobility and low spin scattering compared with their amorphous or polycrystalline counterparts.T...Single crystals of organic semiconductors with perfect crystal structure and minimal density of defects can exhibit high mobility and low spin scattering compared with their amorphous or polycrystalline counterparts.Therefore,these materials are promising candidates as the spin transport media to obtain long spin relaxation times and spin diffusion lengths in spintronic devices.However,the investigation of spin injection and transport properties in organic single crystals is hindered by the inability to construct devices such as single-crystalline organic spin valves(OSVs).Herein,thin and large organic single crystals of 6,13-bis(triisopropylsilylethynyl)pentacene(TIPS-pentacene)were grown on a liquid substrate and transferred to a target substrate carrying ferromagnetic electrodes to construct single-crystalline OSVs.The magnetoresistance(MR)responses of the single crystals were investigated to study their spin injection and transport properties.MR value as high as 17%was probed with an intermediate layer thickness of 269 nm.More importantly,spin transport was still observed in a single crystal of a thickness up to 457 nm,which was much larger than that of polycrystalline thin film.Our research provides a general methodology for constructing single-crystalline OSVs and paves the way to probe the intrinsic spin transport properties of organic semiconductors based on single crystals.展开更多
The spin transport was investigated in permally （Py）/MgO/Ag junction with lateral spin valve structure. Non-local lateral spin valves measurement was carried out to determin, the apin accumulignal in Ag strip, and t...The spin transport was investigated in permally （Py）/MgO/Ag junction with lateral spin valve structure. Non-local lateral spin valves measurement was carried out to determin, the apin accumulignal in Ag strip, and the spin dif u^sion - length in Ag of the lateral spin valves was extracted from devices with the different distances between injector and detector. The experimental results are found that spin accumulation and spin diffusion length （2s） could be significantly enhanced in Ag strip with MgO capping layer, and those effects may be attributed to the low-surface spin scattering rate in Ag with an MgO cap- ping layer.展开更多
Microstructure of NiO-containing Co/Cu/Co spin valves （CCC-SV） annealed at room temperature for nearly four years has been studied by synchrotron radiation X-ray diffraction. With the annealing time expanding, the t...Microstructure of NiO-containing Co/Cu/Co spin valves （CCC-SV） annealed at room temperature for nearly four years has been studied by synchrotron radiation X-ray diffraction. With the annealing time expanding, the thickness of each sub-layer remains nearly unchanged while the interface roughness varies obviously compared with that of samples without annealing. The roughness at the interface of NiO/Co decreases with the annealing time increasing for both of the samples with NiO layer on the top （TSV） and under the bottom （BSV） of CCC-SV. On the other hand, the roughness at Co/Cu interface increases with the annealing time expanding for BSV while it decreases for TSV. These results indicate that the structure of TSV is more stable than that of BSV.展开更多
Magnetoelectric coupling has been a trending research topic in both organic and inorganic materials and hybrids.The concept of controlling magnetism using an electric field is particularly appealing in energy efficien...Magnetoelectric coupling has been a trending research topic in both organic and inorganic materials and hybrids.The concept of controlling magnetism using an electric field is particularly appealing in energy efficient applications.In this spirit,ferroelectricity has been introduced to organic spin valves to manipulate the magneto transport,where the spin transport through the ferromagnet/organic spacer interfaces(spinterface)are under intensive study.The ferroelectric materials in the organic spin valves provide a knob to vary the interfacial energy alignment and the interfacial crystal structures,both are critical for the spin transport.In this review,we introduce the recent efforts of controlling magnetoresistance of organic spin valves using ferroelectricity,where the ferroelectric material is either inserted as an interfacial layer or used as a spacer material.The realization of the ferroelectric control of magneto transport in organic spin valve,advances our understanding in the spin transport through the ferromagnet/organic interface,and suggests more functionality of organic spintronic devices.展开更多
基金performed within the framework of State Assignment from the Ministry of Education and Science of Russian Federation (topic Spin, No. 122021000036-3 and topic Magnet, No. 122021000034-9)partially supported by the Russian Foundation for Basic Research (project No. 2042-660018)。
文摘Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive properties was revealed. Bending deformation was applied to the microobjects based on the flexible spin valves in parallel to anisotropy axes. It was revealed that during the bend the magnetoresistance changes due to the joint impact of both the change of the magnetic field projection on the film plane and the change of the magnetic properties of the ferromagnetic layers. The obtained dependences have been used in construction of bending sensor, in which the flexible spin valve microstripes were united into the Wheatstone bridge.
基金supported by the National Natural Science Foundation of China(Grant No.11404322)the Natural Science Foundation of Huai’an(Grant Nos.HAB202229 and HAB202150)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.22KJD140002)。
文摘A single-molecule magnet is a long-sought-after nanoscale component because it can enable us to miniaturize nonvolatile memory storage devices.The signature of a single-molecule magnet is switching between two bistable magnetic ground states under an external magnetic field.Based on this feature,we theoretically investigate a magnetic-fieldcontrolled reversible resistance change active at low temperatures in a molecular magnetic tunnel junction,which consists of a single-molecule magnet sandwiched between a ferromagnetic electrode and a normal metal electrode.Our numerical results demonstrate that the molecular magnetism orientation can be manipulated by magnetic fields to be parallel/antiparallel to the ferromagnetic electrode magnetization.Moreover,different magnetic configurations can be“read out”based on different resistance states or different spin polarization parameters in the current spectrum,even in the absence of a magnetic field.Such an external magnetic field-controlled resistance state switching effect is similar to that in traditional spin valve devices.The difference between the two systems is that one of the ferromagnetic layers in the original device has been replaced by a magnetic molecule.This proposed scheme provides the possibility of better control of the spin freedom of electrons in molecular electrical devices,with potential applications in future high-density nonvolatile memory devices.
基金financially supported by the National Natural Science Foundation of China (Nos. 61025021and 60936002)the National Key Project of Scienceand Technology of China (Nos. 2009ZX02023-001-3 and 2011ZX02403-002)the Independent Scientific Research of Tsinghua University (No. 2010THZ0)
文摘The magnetoresistance behavior and the magnetization reversal mode of NiFe/Cu/CoFe/IrMn spin valve giant magnetoresistance （SV-GMR） in nanoscale were investigated experimentally and theoretically by nanosized magnetic simulation methods. Based on the Landau-Lifshitz-Gilbert equation, a model with a special gridding was proposed to calculate the giant magnetoresistance ratio （MR） and investigate the magnetization reversal mode. The relationship between MR and the external magnetic field was obtained and analyzed. Studies into the variation of the magnetization distribution reveal that the magnetization reversal mode, that is, the jump variation mode for NiFe/Cu/CoFe/IrMn, depends greatly on the antiferromagnetic coupling behavior between the pinned layer and the antiferromagnetic layer. It is also found that the switching field is almost linear with the exchange coefficient.
基金supported by the National Natural Science Foundation of China(Grant No.11547127)the China Postdoctoral Science Foundation(Grant No.2017M611852)the Natural Science Foundation for Colleges and Universities in Jiangsu Province,China(Grant No.13KJB140005)
文摘We propose two possible spin valves based on a zigzag silicene nanoribbon（ZSR） ferromagnetic junction. By using the Landauer–B u¨tikker formula, we calculate the spin-resolved conductance spectrum of the system and find that the spin transport is crucially dependent on the band structure of the ZSR tuned by a perpendicular electric field. When the ZSR is in the topological insulator phase under a zero electric field, the low-energy spin transport and its ON and OFF states in the tunneling junction mainly rely on the valley valve effect and the edge state of the energy band, which can be electrically modulated by the Fermi level, the spin–orbit coupling, and the local magnetization. When a nonzero perpendicular electric field is applied, the ZSR is a band insulator with a finite energy gap, the spin switch phenomenon is still preserved in the device and it does not come from the valley valve effect, but from the energy gap opened by the perpendicular electric field. The proposed device might be designed as electrical tunable spin valves to manipulate the spin degree of freedom of electrons in silicene.
基金supported by the Yunnan Provincial Ten Thousand Talents Plan Young Talents Training Fund,China(Grant No.KKRD201952029)the Applied Basic Research Program of Yunnan Province,China(Grant No.2011FB037)the School Talent Cultivation Foundation,China(Grant No.KKSY201252017)。
文摘A multilayered spin valve film with a structure of Ta(5 nm)/Co_(75)Fe_(25)(5 nm)/Cu(2.5 nm)/Co_(75)Fe_(25)(5 nm)/Ir_(20)Mn_(80)(12 nm)/Ta(8 nm)is prepared by the high-vacuum direct current(DC)magnetron sputtering.The effect of temperature on the spin valve structure and the magnetic properties are studied by x-ray diffraction(XRD),atomic force microscopy(AFM),and vibrating sample magnetometry.The effect of temperature on the exchange bias field thermomagnetic properties of multilayered spin valve is studied by the residence time of samples in a reverse saturation field.The results show that as the temperature increases,the IrMn(111)texture weakens,surface/interface roughness increases,and the exchange bias field decreases.Below 200℃,the exchange bias field decreases with the residence time increasing,and at the beginning of the negative saturation field,the exchange bias field Hex decreases first quickly and then slowly gradually.When the temperature is greater than 200℃,the exchange bias field is unchanged with the residence time increasing.
基金the National Natural Science Foundation of China （Grant No. 10174014, 60271013, 10321003, 60490290） the State Key Project of Fundamental Research （No. 001CB610602 , 2002CB613504） the Hong Kong RGC Grant （HKUST6165/01P）.
文摘Top and bottom NiO-pinning spin valves of Si/Ta/NiO/Co/Cu/Co/Ta and Si/Ta/Co/Cu/Co/NiO/Ta were prepared by magnetron sputtering, and X-ray diffraction and giant magnetoresistance （GMR） ratio were measured in the temperature range from 5 to 300 K. For the bottom spin valve, the interracial roughness at NiO/Co is much smaller than that of Co/NiO in the top one. The Co/Cu and Cu/Co interfaces have the same roughness in the bottom and the top spin valves. NiO, Co, and Cu layers have （111） preferred orientations in the top one and random orientations in the bottom one. The GMR ratio of the bottom spin valve is larger than that of the top one at all temperatures and their difference increases with decreasing temperature.
基金supported by the National Basic Research Program of China (2014CB921104)the National Natural Science Foundation of China (Grant Nos. 51222103, 11274113, 11474067, and 51171047)the support from the Program for New Century Excellent Talents in University (NCET-12-0132)
文摘The exchange-coupled [Co/Ni]N/Tb Fe nano-magnetic films can display strong perpendicular magnetic anisotropy(PMA) which depends on the Tb:Fe component ratio, Tb Fe layer thickness and the repetition number N of [Co/Ni]Nmultilayer. Perpendicular spin valves in the nano thickness scale, consisting of a [Co/Ni]3free and a [Co/Ni]5/Tb Fe reference multilayer, show high giant magnetoresistance(GMR) signal of 6.5 % and a large switching field difference over3 k Oe. However, unexpected slanting of the free layer magnetization, accompanied by a reduced GMR ratio, was found to be caused by the presence of a thick Fe-rich or even a thin but Tb-rich Tb Fe layer. We attribute this phenomenon to the large magnetostriction effect of Tb Fe which probably induces strong stress acting on the free layer and hence reduces its interfacial PMA.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11304381 and 11374244)the Research Funds of Renmin University of China(Grant No.17XNLF02)+1 种基金the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.201443)the Natural Science Foundation of Fujian Province of China(Grant No.2015J06016)
文摘Spin injection, spin diffusion, and spin detection are investigated in Co/Ag/Co lateral spin valves at room temperature.Clear spin accumulation signals are detected by the non-local measurement. By fitting the results to the one-dimensional diffusion equation,8.6% spin polarization of the Co/Ag interface and -180 nm spin diffusion length in Ag are obtained.Thermal treatment results show that the spin accumulation signal drastically decreases after 100℃ annealing, and disappears under 200℃ annealing. Our results demonstrate that, compared to the spin diffusion length, the decrease and the disappearance of the spin accumulation signal are mainly dominated by the variation of the interfacial spin polarization of the Co/Ag interface.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11404013,11605003,61405003,11174020 and 11474012the Scientific Research Project of Beijing Educational Committee under Grant No KM201510011002the 2016 Graduate Research Program of Beijing Technology and Business University
文摘The extra heat generation in spin transport is usually interpreted in terms of the spin relaxation. Reformulating the heat generation rate, we find alternative current-force pairs without cross effects, which enable us to interpret the product of each pair as a distinct mechanism of heat generation. The results show that the spin-dependent part of the heat generation includes two terms. One is proportional to the square of the spin accumulation and arises from the spin relaxation. However, the other is proportional to the square of the spin-accumulation gradient and should be attributed to another mechanism, the spin diffusion. We illustrate the characteristics of the two mechanisms in a typical spin valve with a finite nonmagnetic spacer layer.
基金financially supported by the National Key Research and Development Program of China(grant no.2017YFA0207500)the National Natural Science Foundation of China(grant nos.51973153 and 11774254).
文摘Interface engineering in device fabrication is a significant but complicated issue.Although great successes have been achieved by conventional physical in situ or ex situ methods,it still suffers from complicated procedures.In this work,we present a facile method for fabricating phthalocyanine(Pc)-based two-dimensional conductive metal–organic framework(MOF)films.Based on PcM-Cu(M=Ni,Cu,H_(2))MOF films,spin valves with a vertical configuration of La_(0.67)Sr_(0.33)MnO_(3)/PcM-Cu MOFs/Co were constructed successfully,and exhibited notably high negative magnetoresistance(MR)up to -22% at 50 K.The penetrated Co atoms coordinated with the dehydrogenated hydroxy groups in the MOFs resulting in an antiferromagnetic layer of the PcM-Cu-Co hybrid structure.Interestingly,a significant exchange bias effect was demonstrated at the PcM-Cu MOF/Co interface,beneficial for the MR behavior.Thus,our present study provides new insights into developing high-performance organic spin valves via de novo molecular design.
基金supported by the National Natural Sci-ence Foundation of China(91750101,21733001,52072168,51861145201)the National Key Basic Research Program of the Ministry of Science and Technology of China(2018YFA0306200,2021YFA1202901)+1 种基金the Fundamental Research Funds for the Central Universities(021314380078,021314380104,021314380147)Jiangsu Key Laboratory of Artificial Functional Materials.
文摘Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MTJ devices has been proposed in two directions:improving device performance by utilizing advanced two-dimensional(2D)ferromagnetic materials or extending device functionalities by exploring the gate-tunable magnetic properties of ferromagnets.Based on the recent development of 2D magnets with the ease of external stimuli,such as electric field,due to their reduced dimensions,reliable prospects for gate-tunable MTJ devices can be achieved,shedding light on the great potential of next-generation MTJs with multiple functionalities for various application environments.While the electrical gate-tunable MTJ device is highly desirable for practical spintronic devices,it has not yet been demonstrated.Here,we demonstrate the experimental realization of a spin valve device by combining a vertical Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ with an electrolyte gate.The magnetoresistance ratio(MR ratio)of 36%for the intrinsic MTJ confirms the good performance of the device.By electrolyte gating,the tunneling MR ratio of Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ can be elevated 2.5 times,from 26%to 65%.Importantly,the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating,providing a promising method to control the magnetization configuration of the MTJ.Our work demonstrates a gate-tunable MTJ device toward the possibility for gate-controlled spintronic devices,paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.
基金financially supported by the National Natural Science Foundation of China (Nos. 11174020, 51331002, and 51371027)the Fundamental Research Funds for the Central Universities FRF-SD-12-011A
文摘Pseudo spin valves（SVs） exhibiting perpendicular magnetic anisotropy were prepared by magnetron sputtering. Magnetization measurements of the Co/Pt multilayers were performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect, and proper coercivity. The optimal reference layer and free layer are Pt（5.0 nm）/[Co（0.4 nm）/Pt（0.6 nm）]3/Co（0.4 nm）/Cu（3.0 nm）and Cu（3.0 nm）/[Co（0.4 nm）/Pt（1.5 nm）]4, respectively.The resulting pseudo SV exhibits two well-separated hysteresis loops when the field is applied perpendicular to the film plane. The minor hysteresis loop corresponding to the free layer shifts toward negative direction of the magnetic field axis, indicating ferromagnetic interlayer exchange coupling between the two magnetic layers. The coupling also enhances the coercivity（HC） of both layers. The perpendicular giant magnetoresistance（GMR） of 2.7 % is achieved with current in plane measurement. The GMR first increases when Pt seed layer is thickened, reaches a maximum of 3.0 % at 4 nm and then decreases with the further increase of thickness. But thicker Cu spacer layer always lowers the GMR of the SV.
基金supported by the National Key R&D Program of China (2017YFA0303400 and 2017YFB0405700)the National Natural Science foundation of China (61774144)+2 种基金Beijing Natural Science Foundation Key Program (Z190007)the Project from Chinese Academy of Sciences (QYZDY-SSW-JSC020, XDPB12, and XDB28000000)K C Wong Education Foundation。
文摘Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to realize novel functionalities.Here,we report the fabrication of multi-state vertical spin valves without spacer layers by using vd W homo-junctions in which exfoliated Fe3GeTe2 nanoflakes act as ferromagnetic electrodes and/or interlayers.We demonstrate the typical behavior of two-state and threestate magnetoresistance for devices with two and three Fe3GeTe2 nanoflakes,respectively.Distinct from traditional spin valves with sandwich structures,our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices.Our work demonstrates the possibility of extend multi-state,non-volatile spin information to 2 D magnetic homo-junctions,and it emphasizes the utility of vd W interface as a fundamental building block for spintronic devices.
文摘When spins are injected through graphene layers from a transition metal ferromagnet, high spin polarization can be achieved. When detected by another ferromagnet, the spin-polarized current makes high- and low-resistance states in a ferromagnet/graphene/ferromagnet junction. Here, we report manifest spin valve effects from room temperature to 10 K in junctions comprising NiFe electrodes and an interlayer made of double-layer or single-layer graphene grown by chemical vapor deposition. We have found that the spin valve effect is stronger with double-layer graphene than with single-layer graphene. The ratio of relative magnetoresistance increases from 0.09% at room temperature to 0.14% at 10 K for single-layer graphene and from 0.27% at room temperature to 0.48% at 10 K for double-layer graphene. The spin valve effect is perceived to retain the spin-polarized transport in the vertical direction and the hysteretic nature of magnetoresistance provides the basic functionality of a memory device. We have also found that the junction resistance decreases monotonically as temperature is lowered and the current-voltage characteristics show linear behaviour. These results revealed that a graphene interlayer works not as a tunnel barrier but rather as a conducting thin film between two NiFe electrodes.
基金The authors acknowledge financial support from the National Key R&D Program of China (Nos. 2016YFB0401100 and 2017YFA0204503)the National Natural Science Foundation of China (Nos. 52003190, 51633006, 91833306, 21875158, 51703159, and 51733004).
文摘Organic spin valve (OSV), one of the most promising and representative devices involving spin injection, transport and detection, has drawn tremendous attention owing to their ultra-long spin relaxation time in the field of molecular spintronics. Since the first demonstration of truly worked vertical OSV device in 2004, efforts in enhancement of high performance and pursuit of spin-related nature have been devoted in related field. It offers a new opportunity to develop the integrated flexible multi-functional arrays based on spintronics in the future. However, the unreliable working state in OSVs due to the lack of exploration on interface control will cause severe impact on the performance evaluation and further restrict their practical application. Herein, we focus on the recent progress in strategies for reliable fabrication and evaluation of typical OSVs in vertical configuration. Firstly, the challenges in protection of two spin interface properties and identification of spin-valve-like signals were proposed. Then, three points for attention including selection of bottom electrodes, optimization of organic spacer, and prevention of metal penetration to improve the device performance and reliability were mentioned. Particularly, various modified strategies to solve the “dead layer” issue were highlighted. Furthermore, we discussed the general protocols in the reliable evaluation of OSVs’ performance and transport mechanism identification. Notably, several key fundamentals resulting in spurious magnetoresistance (MR) response were illustrated. Finally, we also highlighted the future perspectives on spintronic devices of organic materials.
基金the National Key R&D Program(Nos.2016YFB0401100,2017YFA0204503)the National Natural Science Foundation of China(Nos.91833306,21875158,51633006,51703159,51733004).The authors acknowledge the Laboratory of Microfabrication,Institute of Physics,CAS,for their assistance in electrode fabrication。
文摘The spinterface formed between ferromagnetic(FM)electrode and organic materials is vital for performance optimization in organic spin valve(OSV).Half-metallic Fe_(3)O_(4)with drastic change in structure,conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator.However,such modulating effect of Fe_(3)O_(4)in OSV has not been comprehensively investigated,especially below the Verwey transition temperature(Tv).Here,we highlight the important role of Fe_(3)O_(4)electrode in reliable-working and controllable Fe_(3)O_(4)/P3HT/Co polymer spin valves by investigating the magnetoresistance(MR)above and below 7V.In order to distinguish between different contributions to charge transport and related MR responses,the systematic electronic and magnetic characterizations were carried out in full temperature range.Particularly,the first-order metal-insulator transition in Fe_(3)O_(4)has a dramatic effect on the MR enhancement of polymer spin valves at 7V.Moreover,both the conducting mode transformation and MR line shape modulation could be accomplished across 7V.This research renders unique scenario to multimodal storage by external thermodynamic parameters,and further reveals the importance of spin-dependent interfacial modification in polymer spin valves.
基金the National Natural Science Foundation of China(61674116,51873148,51633006,and 52003190)the Ministry of Science and Technology of China(2016YFA0202302)the Natural Science Foundation of Tianjin(18JC-YBJC18400)。
文摘Single crystals of organic semiconductors with perfect crystal structure and minimal density of defects can exhibit high mobility and low spin scattering compared with their amorphous or polycrystalline counterparts.Therefore,these materials are promising candidates as the spin transport media to obtain long spin relaxation times and spin diffusion lengths in spintronic devices.However,the investigation of spin injection and transport properties in organic single crystals is hindered by the inability to construct devices such as single-crystalline organic spin valves(OSVs).Herein,thin and large organic single crystals of 6,13-bis(triisopropylsilylethynyl)pentacene(TIPS-pentacene)were grown on a liquid substrate and transferred to a target substrate carrying ferromagnetic electrodes to construct single-crystalline OSVs.The magnetoresistance(MR)responses of the single crystals were investigated to study their spin injection and transport properties.MR value as high as 17%was probed with an intermediate layer thickness of 269 nm.More importantly,spin transport was still observed in a single crystal of a thickness up to 457 nm,which was much larger than that of polycrystalline thin film.Our research provides a general methodology for constructing single-crystalline OSVs and paves the way to probe the intrinsic spin transport properties of organic semiconductors based on single crystals.
基金financially supported by the National Natural Science Foundation of China(Nos.11304381 and 11174366)the Research Funds of Renmin University of China(No.13XNLF02)
文摘The spin transport was investigated in permally （Py）/MgO/Ag junction with lateral spin valve structure. Non-local lateral spin valves measurement was carried out to determin, the apin accumulignal in Ag strip, and the spin dif u^sion - length in Ag of the lateral spin valves was extracted from devices with the different distances between injector and detector. The experimental results are found that spin accumulation and spin diffusion length （2s） could be significantly enhanced in Ag strip with MgO capping layer, and those effects may be attributed to the low-surface spin scattering rate in Ag with an MgO cap- ping layer.
基金Supported by Open Project of Lab of Solid State Microstructures of Nanjing University (M06007)Doctoral Foundation of Hohai University (2084/40701117)Natural Science Foundation of Hohai University (2084/408307)
文摘Microstructure of NiO-containing Co/Cu/Co spin valves （CCC-SV） annealed at room temperature for nearly four years has been studied by synchrotron radiation X-ray diffraction. With the annealing time expanding, the thickness of each sub-layer remains nearly unchanged while the interface roughness varies obviously compared with that of samples without annealing. The roughness at the interface of NiO/Co decreases with the annealing time increasing for both of the samples with NiO layer on the top （TSV） and under the bottom （BSV） of CCC-SV. On the other hand, the roughness at Co/Cu interface increases with the annealing time expanding for BSV while it decreases for TSV. These results indicate that the structure of TSV is more stable than that of BSV.
基金This project was primarily supported by the National Science Foundation through the Nebraska Materials Research Science and Engineering Center(Grant No.DMR-1420645).
文摘Magnetoelectric coupling has been a trending research topic in both organic and inorganic materials and hybrids.The concept of controlling magnetism using an electric field is particularly appealing in energy efficient applications.In this spirit,ferroelectricity has been introduced to organic spin valves to manipulate the magneto transport,where the spin transport through the ferromagnet/organic spacer interfaces(spinterface)are under intensive study.The ferroelectric materials in the organic spin valves provide a knob to vary the interfacial energy alignment and the interfacial crystal structures,both are critical for the spin transport.In this review,we introduce the recent efforts of controlling magnetoresistance of organic spin valves using ferroelectricity,where the ferroelectric material is either inserted as an interfacial layer or used as a spacer material.The realization of the ferroelectric control of magneto transport in organic spin valve,advances our understanding in the spin transport through the ferromagnet/organic interface,and suggests more functionality of organic spintronic devices.
