The origin of ferromagnetism in epitaxial strained LaCoO_(3-x)films has long been controversial.Here,we investigated the magnetic behavior of a series of oxygen vacancy-ordered LaCoO_(3-x)films on different substrates...The origin of ferromagnetism in epitaxial strained LaCoO_(3-x)films has long been controversial.Here,we investigated the magnetic behavior of a series of oxygen vacancy-ordered LaCoO_(3-x)films on different substrates.Obvious ferromagnetism was observed in perovskite LaCoO_(3)/LSAT(LSAT=(LaAlO_(3))0.3(SrAlTaO_(6))_(0.7))and LaCoO_(3)/SrTiO_(3) films,while LaCoO_(3)/LaAlO_(3)films showed weak ferromagnetic behavior.Meanwhile,LaCoO_(2.67) films exhibited antiferromagnetic behavior.An unexpected low-temperature ferromagnetic phenomenon with a Curie temperature of~83 K and a saturation magnetization of~1.2μB/Co was discovered in 15 nm thick LaCoO_(2.5)/LSAT thin films,which is probably related to the change in the interface CoO_(6) octahedron rotation pattern.Meanwhile,the observed ferromagnetism gradually disappeared as the thickness of the film increased,indicating a relaxation of tensile strain.Analysis suggests that the rotation and rhombohedral distortion of the CoO_(6) octahedron weakened the crystal field splitting and promoted the generation of the ordered high-spin state of Co^(2+).Thus the super-exchange effect between Co^(2+)(high spin state),Co^(2+)(low spin state)and Co^(2+)(high spin state)produced a low-temperature ferromagnetic behavior.However,compressive-strained LaCoO_(2.5)film on a LaAlO_(3)substrate showed normal anti-ferromagnetic behavior.These results demonstrate that both oxygen vacancies and tensile strain are correlated with the emergent magnetic properties in epitaxial LaCoO_(3-x)films and provide a new perspective to regulate the magnetic properties of transition oxide thin films.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2020YFA0711502 and 2019YFA0704900)the National Natural Sciences Foundation of China(Grant Nos.52088101,51971240,and 11921004)the Key Program of the Chinese Academy of Sciences and the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB33030200)。
文摘The origin of ferromagnetism in epitaxial strained LaCoO_(3-x)films has long been controversial.Here,we investigated the magnetic behavior of a series of oxygen vacancy-ordered LaCoO_(3-x)films on different substrates.Obvious ferromagnetism was observed in perovskite LaCoO_(3)/LSAT(LSAT=(LaAlO_(3))0.3(SrAlTaO_(6))_(0.7))and LaCoO_(3)/SrTiO_(3) films,while LaCoO_(3)/LaAlO_(3)films showed weak ferromagnetic behavior.Meanwhile,LaCoO_(2.67) films exhibited antiferromagnetic behavior.An unexpected low-temperature ferromagnetic phenomenon with a Curie temperature of~83 K and a saturation magnetization of~1.2μB/Co was discovered in 15 nm thick LaCoO_(2.5)/LSAT thin films,which is probably related to the change in the interface CoO_(6) octahedron rotation pattern.Meanwhile,the observed ferromagnetism gradually disappeared as the thickness of the film increased,indicating a relaxation of tensile strain.Analysis suggests that the rotation and rhombohedral distortion of the CoO_(6) octahedron weakened the crystal field splitting and promoted the generation of the ordered high-spin state of Co^(2+).Thus the super-exchange effect between Co^(2+)(high spin state),Co^(2+)(low spin state)and Co^(2+)(high spin state)produced a low-temperature ferromagnetic behavior.However,compressive-strained LaCoO_(2.5)film on a LaAlO_(3)substrate showed normal anti-ferromagnetic behavior.These results demonstrate that both oxygen vacancies and tensile strain are correlated with the emergent magnetic properties in epitaxial LaCoO_(3-x)films and provide a new perspective to regulate the magnetic properties of transition oxide thin films.
