中国物理B ›› 2023, Vol. 32 ›› Issue (8): 87504-087504.doi: 10.1088/1674-1056/acafdc

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Low-temperature ferromagnetism in tensile-strained LaCoO2.5 thin film

Yang-Yang Fan(范洋洋)1,2, Jing Wang(王晶)1,3,†, Feng-Xia Hu(胡凤霞)1,3,4,‡, Bao-He Li(李宝河)2,§, Ai-Cong Geng(耿爱丛)2, Zhuo Yin(殷卓)1,3, Cheng Zhang(张丞)1,3, Hou-Bo Zhou(周厚博)1,3, Meng-Qin Wang(王梦琴)1,3, Zi-Bing Yu(尉紫冰)1,3, and Bao-Gen Shen(沈保根)1,3,4,5   

  1. 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
  • 收稿日期:2022-09-16 修回日期:2022-11-11 接受日期:2023-01-04 发布日期:2023-07-27
  • 通讯作者: Jing Wang, Feng-Xia Hu, Bao-He Li E-mail:wangjing@.iphy.ac.cn;fxhu@.iphy.ac.cn;lbhe@th.btbu.edu.cn
  • 基金资助:
    This work was 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).

Low-temperature ferromagnetism in tensile-strained LaCoO2.5 thin film

Yang-Yang Fan(范洋洋)1,2, Jing Wang(王晶)1,3,†, Feng-Xia Hu(胡凤霞)1,3,4,‡, Bao-He Li(李宝河)2,§, Ai-Cong Geng(耿爱丛)2, Zhuo Yin(殷卓)1,3, Cheng Zhang(张丞)1,3, Hou-Bo Zhou(周厚博)1,3, Meng-Qin Wang(王梦琴)1,3, Zi-Bing Yu(尉紫冰)1,3, and Bao-Gen Shen(沈保根)1,3,4,5   

  1. 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
  • Received:2022-09-16 Revised:2022-11-11 Accepted:2023-01-04 Published:2023-07-27
  • Contact: Jing Wang, Feng-Xia Hu, Bao-He Li E-mail:wangjing@.iphy.ac.cn;fxhu@.iphy.ac.cn;lbhe@th.btbu.edu.cn
  • Supported by:
    This work was 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 LaCoO3-x films has long been controversial. Here, we investigated the magnetic behavior of a series of oxygen vacancy-ordered LaCoO3-x films on different substrates. Obvious ferromagnetism was observed in perovskite LaCoO3/LSAT (LSAT = (LaAlO3)0.3(SrAlTaO6)0.7) and LaCoO3/SrTiO3 films, while LaCoO3/LaAlO3 films showed weak ferromagnetic behavior. Meanwhile, LaCoO2.67 films exhibited antiferromagnetic behavior. An unexpected low-temperature ferromagnetic phenomenon with a Curie temperature of ~ 83 K and a saturation magnetization of ~ 1.2 μB/Co was discovered in 15 nm thick LaCoO2.5/LSAT thin films, which is probably related to the change in the interface CoO6 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 CoO6 octahedron weakened the crystal field splitting and promoted the generation of the ordered high-spin state of Co2+. Thus the super-exchange effect between Co2+ (high spin state), Co2+ (low spin state) and Co2+(high spin state) produced a low-temperature ferromagnetic behavior. However, compressive-strained LaCoO2.5 film on a LaAlO3 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 LaCoO3-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

Abstract: The origin of ferromagnetism in epitaxial strained LaCoO3-x films has long been controversial. Here, we investigated the magnetic behavior of a series of oxygen vacancy-ordered LaCoO3-x films on different substrates. Obvious ferromagnetism was observed in perovskite LaCoO3/LSAT (LSAT = (LaAlO3)0.3(SrAlTaO6)0.7) and LaCoO3/SrTiO3 films, while LaCoO3/LaAlO3 films showed weak ferromagnetic behavior. Meanwhile, LaCoO2.67 films exhibited antiferromagnetic behavior. An unexpected low-temperature ferromagnetic phenomenon with a Curie temperature of ~ 83 K and a saturation magnetization of ~ 1.2 μB/Co was discovered in 15 nm thick LaCoO2.5/LSAT thin films, which is probably related to the change in the interface CoO6 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 CoO6 octahedron weakened the crystal field splitting and promoted the generation of the ordered high-spin state of Co2+. Thus the super-exchange effect between Co2+ (high spin state), Co2+ (low spin state) and Co2+(high spin state) produced a low-temperature ferromagnetic behavior. However, compressive-strained LaCoO2.5 film on a LaAlO3 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 LaCoO3-x films and provide a new perspective to regulate the magnetic properties of transition oxide thin films.

Key words: transition metal oxides films, oxygen vacancy, topological phase transitions, magnetism

中图分类号:  (Magnetic properties of thin films, surfaces, and interfaces)

  • 75.70.-i
75.30.Kz (Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)) 75.47.Lx (Magnetic oxides) 72.15.-v (Electronic conduction in metals and alloys)