Low-temperature ferromagnetism in tensile-strained LaCoO_(2.5)thin film  

作　　者：范洋洋 王晶 胡凤霞 李宝河 耿爱丛 殷卓 张丞 周厚博 王梦琴 尉紫冰 沈保根 Yang-Yang Fan;Jing Wang;Feng-Xia Hu;Bao-He Li;Ai-Cong Geng;Zhuo Yin;Cheng Zhang;Hou-Bo Zhou;Meng-Qin Wang;Zi-Bing Yu;Bao-Gen Shen(Beijing National Laboratory for Condensed Matter Physics and State Key Laboratory of Magnetism,Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China;School of Physics,Beijing Technology and Business University,Beijing 100048,China;School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 101408,China;Songshan Lake Materials Laboratory,Dongguan 523808,China;Ningbo Institute of Materials Technology and Engineering,Chinese Academy of Sciences,Ningbo 315201,China)

机构地区：[1]Beijing National Laboratory for Condensed Matter Physics and State Key Laboratory of Magnetism,Institute of Physics,Chinese Academy of Sciences,Beijing 100190,China [2]School of Physics,Beijing Technology and Business University,Beijing 100048,China [3]School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 101408,China [4]Songshan Lake Materials Laboratory,Dongguan 523808,China [5]Ningbo Institute of Materials Technology and Engineering,Chinese Academy of Sciences,Ningbo 315201,China

出　　处：《Chinese Physics B》2023年第8期439-445,共7页中国物理B（英文版）

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)。

摘　　要：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.

关 键 词：transition metal oxides films oxygen vacancy topological phase transitions MAGNETISM 

分 类 号：O469[理学—凝聚态物理]