Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, whic...Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.展开更多
Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely ...Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor- phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper- ties of Gal-xHoxN （x=0.0, 0.05） films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films （i.e. GaN） exhibited diamagnetic behavior, while the Ho-doped （Gao.95Hoo.05N） film exhibited a ferro- magnetic behavior.展开更多
Cux（Cu2O）1-x（0.09 x 1.00） granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cux（C...Cux（Cu2O）1-x（0.09 x 1.00） granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cux（Cu2O）1-x deposition. Room-temperature ferromagnetism（FM） is found in all of the samples. The saturated magnetization increases at first and then decreases with the decrease of x. The photoluminescence spectra show that the magnetization is closely correlated with the Cu vacancies in the Cux（Cu2O）1-x granular films. Fundamentally, the FM could be understood by the Stoner model based on the charge transfer mechanism. These results may provide solid evidence and physical insights on the origin of FM in the Cu2O-based oxides diluted magnetic semiconductors, especially for systems without intentional magnetic atom doping.展开更多
Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto- combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of ...Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto- combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X- ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.展开更多
The electronic structure and magnetic properties of single layer Ga_(2)O_(3)in the presence of Ga and O vacancies are studied by first principles method based on density functional theory.The results show that the int...The electronic structure and magnetic properties of single layer Ga_(2)O_(3)in the presence of Ga and O vacancies are studied by first principles method based on density functional theory.The results show that the introduction of Ga vacancy(VGa)leads to a non-zero magnetic moment in singlelayer two-dimensional(2D)Ga_(2)O_(3),while VO does not.We find that Ga vacancies in two different symmetric positions can lead to spin polarized ground states.Notably,when the VGa ratio is greater than 1/16(indicating one Ga vacancy per 16 Ga atoms),single-layer 2D Ga_(2)O_(3)exhibits semi-metallic properties and its spin polarization reaches 100%at the Fermi level.Calculations of these two Ga vacancy systems also indicate a potential long-range ferromagnetic order at a high Curie temperature(355.8 K).Finally,a single layer 2D Ga_(2)O_(3)with high GaI vacancy(VGaI)ratio can be used as the ferromagnetic layer to obtain the magnetic tunnel junction(MTJ)with high spin filtering effect at the Fermi level.Ga vacant Ga_(2)O_(3)/MgO/Ga vacant Ga_(2)O_(3)MTJ exhibits excellent spin-filtering effect(with 100%spin polarization)and a giant tunneling magneto resistance(TMR)ratio(up to 1.12×10^(3)%).The results of this paper show that the MTJ based on two-dimensional Ga_(2)O_(3)with room temperature ferromagnetism exhibits reliable performance,showing the possibility of potential applications in spintronics.展开更多
Although many emerging new phenomena have been unraveled in two dimensional(2D)materials with long-range spin orderings,the usually low critical temperature in van der Waals(vdW)magnetic material has thus far hindered...Although many emerging new phenomena have been unraveled in two dimensional(2D)materials with long-range spin orderings,the usually low critical temperature in van der Waals(vdW)magnetic material has thus far hindered the related practical applications.Here,we show that ferromagnetism can hold above 300 K in a metallic phase of 1T-CrTe2 down to the ultra-thin limit.It thus makes CrTe2 so far the only known exfoliated ultra-thin vdW magnets with intrinsic long-range magnetic ordering above room temperature.An in-plane room-temperature negative anisotropic magnetoresistance(AMR)was obtained in ultra-thin CrTe2 devices,with a sign change in the AMR at lower temperature,with−0.6%and+5%at 300 and 10 K,respectively.Our findings provide insights into magnetism in ultra-thin CrTe2,expanding the vdW crystals toolbox for future room-temperature spintronic applications.展开更多
A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a clu...A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.展开更多
Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） chara...Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.展开更多
This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the ...This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.展开更多
[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observe...[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization asc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. asc was reduced from 11.7% （and 10.5%） at 90 K to 7.31% （and 5.93%） at room temperature for d=3 （and d=10）. And η was reduced from 39.5% （and 35.5%） at 90 K to 24.7% （and 20.0%） at room temperature for d=3 （and d=10）.展开更多
The Zn1-xCuxO polycrystalline materials were prepared by doping CuO into wurtzite ZnO through solid state reaction. The high concentration of copper doping in ZnO exhibited remarkable room temperature ferromagnetism. ...The Zn1-xCuxO polycrystalline materials were prepared by doping CuO into wurtzite ZnO through solid state reaction. The high concentration of copper doping in ZnO exhibited remarkable room temperature ferromagnetism. The Experiments showed that the magnetization saturation rose with the increase of Cu content. For the low Cu content sample, the hysteresis loop was slightly tilted which indicated that the diamagnetism coexisted in this sample. The temperature dependence of magnetization of Zn1-xCuxO revealed that the magnetic exchange coupling depended on the doping concentration of Cu and there were many different local environments for magnetism. The measured hysteresis loop and temperature dependence of magnetization were overall performance of the magnetism coming from a wide distribution of ferromagnetic exchange couplings.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51372135 and 61176003)the Tsinghua University Initiative Scientific Research Program,China
文摘Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.
文摘Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor- phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper- ties of Gal-xHoxN （x=0.0, 0.05） films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films （i.e. GaN） exhibited diamagnetic behavior, while the Ho-doped （Gao.95Hoo.05N） film exhibited a ferro- magnetic behavior.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11104148,51101088,and 51171082)the Tianjin Natural Science Foundation,China(Grant Nos.14JCZDJC37700 and 13JCQNJC02800)+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20110031110034)the Fundamental Research Funds for the Central Universities,China
文摘Cux（Cu2O）1-x（0.09 x 1.00） granular films with thickness about 280 nm have been fabricated by direct current reactive magnetron sputtering. The atomic ratio x can be controlled by the oxygen flow rate during Cux（Cu2O）1-x deposition. Room-temperature ferromagnetism（FM） is found in all of the samples. The saturated magnetization increases at first and then decreases with the decrease of x. The photoluminescence spectra show that the magnetization is closely correlated with the Cu vacancies in the Cux（Cu2O）1-x granular films. Fundamentally, the FM could be understood by the Stoner model based on the charge transfer mechanism. These results may provide solid evidence and physical insights on the origin of FM in the Cu2O-based oxides diluted magnetic semiconductors, especially for systems without intentional magnetic atom doping.
文摘Mn doped ZnO nano-crystallites were synthesized by state of the art sol-gel derived auto- combustion technique. As-burnt powder was investigated with different characterization techniques to explore the properties of Mn doped ZnO dilute magnetic semiconductor. X- ray diffraction measurements indicate that Mn doped ZnO retain wurtzite type hexagonal crystal structure like ZnO. Compositional and morphological studies were carried out by energy dispersive X-ray analysis and scanning electron microscopy, respectively. Temperature dependent resistivity of the sample exhibited the semiconducting behavior of the DMS material. Room temperature magnetic properties determined by vibrating sample magnetometer, revealed the presence of ferromagnetic and diamagnetic contributions in Mn doped ZnO.
基金supported by the National Key Research and Development Program of China(2023YFB3609900 and 2021YFA0716400)the General Program of Natural Science Foundation of China(62274134)+4 种基金the National Science Fund for Distinguished Young Scholars(61925404)the Key R&D Project in Xi’an City(2023JH-ZCGJ0013)the Aerospace Institute 771 Innovation Fund(771CX2023007)the Fundamental Research Funds for the Central Universities(YJSJ24020)the Interdisciplinary Cultivation Program of Xidian University(21103240003)。
文摘The electronic structure and magnetic properties of single layer Ga_(2)O_(3)in the presence of Ga and O vacancies are studied by first principles method based on density functional theory.The results show that the introduction of Ga vacancy(VGa)leads to a non-zero magnetic moment in singlelayer two-dimensional(2D)Ga_(2)O_(3),while VO does not.We find that Ga vacancies in two different symmetric positions can lead to spin polarized ground states.Notably,when the VGa ratio is greater than 1/16(indicating one Ga vacancy per 16 Ga atoms),single-layer 2D Ga_(2)O_(3)exhibits semi-metallic properties and its spin polarization reaches 100%at the Fermi level.Calculations of these two Ga vacancy systems also indicate a potential long-range ferromagnetic order at a high Curie temperature(355.8 K).Finally,a single layer 2D Ga_(2)O_(3)with high GaI vacancy(VGaI)ratio can be used as the ferromagnetic layer to obtain the magnetic tunnel junction(MTJ)with high spin filtering effect at the Fermi level.Ga vacant Ga_(2)O_(3)/MgO/Ga vacant Ga_(2)O_(3)MTJ exhibits excellent spin-filtering effect(with 100%spin polarization)and a giant tunneling magneto resistance(TMR)ratio(up to 1.12×10^(3)%).The results of this paper show that the MTJ based on two-dimensional Ga_(2)O_(3)with room temperature ferromagnetism exhibits reliable performance,showing the possibility of potential applications in spintronics.
基金This work is supported by the National Key R&D Program of China(Nos.2019YFA0307800,2017YFA0206302,and 2017YFA0206200)the National Natural Science Foundation of China(NSFC)(Nos.11974357,U1932151,and 51627801)+4 种基金G.Y.and X.H.thank the financial supports from the National Natural Science Foundation of China(NSFC)(No.11874409)This work is supported by the National Natural Science Foundation of China(NSFC)(Nos.61574060,and 8206300210)T.Y.acknowledges supports from the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC,China(No.U1537204)Z.H.acknowledges the support from the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices(No.KF201816)The authors appreciate the help of Dr.Binbin Jiang in obtaining the HAADF-STEM images.
文摘Although many emerging new phenomena have been unraveled in two dimensional(2D)materials with long-range spin orderings,the usually low critical temperature in van der Waals(vdW)magnetic material has thus far hindered the related practical applications.Here,we show that ferromagnetism can hold above 300 K in a metallic phase of 1T-CrTe2 down to the ultra-thin limit.It thus makes CrTe2 so far the only known exfoliated ultra-thin vdW magnets with intrinsic long-range magnetic ordering above room temperature.An in-plane room-temperature negative anisotropic magnetoresistance(AMR)was obtained in ultra-thin CrTe2 devices,with a sign change in the AMR at lower temperature,with−0.6%and+5%at 300 and 10 K,respectively.Our findings provide insights into magnetism in ultra-thin CrTe2,expanding the vdW crystals toolbox for future room-temperature spintronic applications.
基金Project supported by National Key R&D Program of China(2017YFB0305801)the Joint Funds of NSFC-Liaoning(U1508213)。
文摘A novel Fe-Y composite oxide(Fe:Y-6.5) nanocluster was synthesized by self-assembly approach.The α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline with diameter around 10 nm are homogeneously assembled to form a cluster architecture which are constituted of Fe6.5Y composite oxide particles.Additional oxygen vacancies are introduced with cubic-Y_(2)O_(3),and the oxygen vacancies as Fe^(3+)-V_(0)-Y^(3+) between α-Fe_(2)O_(3) and cubic-Y_(2)O_(3) nanocrystalline are generated by self-assembly process.Magnetic hysteresis loops recorded by vibrating sample magnetometry at 273 K display a ferromagnetic order,related to the fact that Fe^(3+)-V_(o)-Y^(3+) act as defect centers in the bound magnetic polaron model for Fe-Y composite oxide nanomaterial.The ferromagnetic prope rties are proportional to oxygen vacancy co ntents,and maximum magnetization(M_(m)) value of the nano-cluster reaches 5.14 A·m^(2)/g.
基金Supported by the National Natural Science Foundation of China under Grant No 20401001, the Key Project of Anhui Provincial Science and Technology Department under Grant No 04022075, the Project of Anhui Provincial Educational Department under Grant No 2004jq113, and the Fund of Laboratory of Solid State Microstructures, Nanjing University under Grant No M031803.
文摘Zn0.99Co0.01O nano-needles are synthesized by using pure ZnO powder as the starting material via chemical reactions in ammonia aqueous solution. The nano-needles show the room-temperature ferromagnetism （RTFM） characterized by using a superconducting quantum interference device. Non-reductive chemical synthesis steps ensure to prevent forming Co-metal nanoclusters within the doped sample. All the results of thermal gravimetric analysis, Fourier transform infrared spectroscopy, x-ray diffraction and ultraviolet spectroscopy demonstrate that Co ions have doped into ZnO lattices and occupied some Zn sites without changing the wurtzite structure of ZnO lattices, and no potential second phase except for the doped Co ions substituting the Zn sites in ZnO lattice can account for the observed RTFM behaviour. Moreover, the synthesis process is of high reproducibility over 80% which is higher than that of commonly-used sol-gel method.
基金Project supported by the Aeronautical Science foundation of China (Grant No 2003ZG51069)the National Defence BaseResearch of China
文摘This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.
基金supported by the State Key Project of Fundamental Research of China No.2007CB924903 and NSFC No.50572053
文摘[FeNi（3 nm）/Zn1-xCoxO（3 nm）]2/ZnO（d nm）/[Zn1-xCoxO（3 nm）/Co（3 nm）]2 （d=3 and 10） semiconductor junctions were prepared by magnetron sputtering system and photolithography. The spin valve effect was observed in these junctions because the utility of the ferromagnetic composite layers acted as soft and hard magnetic layers. The electrical detection was performed by measuring the magnetoresistance of these junctions to investigate the current spin polarization asc in the ZnO layer and the spin injection efficiency η of spin-polarized electrons. asc was reduced from 11.7% （and 10.5%） at 90 K to 7.31% （and 5.93%） at room temperature for d=3 （and d=10）. And η was reduced from 39.5% （and 35.5%） at 90 K to 24.7% （and 20.0%） at room temperature for d=3 （and d=10）.
基金Funded by the Natural Science Foundation of Fujian Province(No.2011J01014)the National Natural Science Foundation of China(No.11074099)
文摘The Zn1-xCuxO polycrystalline materials were prepared by doping CuO into wurtzite ZnO through solid state reaction. The high concentration of copper doping in ZnO exhibited remarkable room temperature ferromagnetism. The Experiments showed that the magnetization saturation rose with the increase of Cu content. For the low Cu content sample, the hysteresis loop was slightly tilted which indicated that the diamagnetism coexisted in this sample. The temperature dependence of magnetization of Zn1-xCuxO revealed that the magnetic exchange coupling depended on the doping concentration of Cu and there were many different local environments for magnetism. The measured hysteresis loop and temperature dependence of magnetization were overall performance of the magnetism coming from a wide distribution of ferromagnetic exchange couplings.
