| Popis: |
The origin of ferromagnetism in epitaxial strained LaCoO3-x films has been a long controversial hitherto. Here, we investigated the magnetic behavior of a series of oxygen vacancies ordered LaCoO3-x films on different substrates. Obvious ferromagnetism was observed in perovskite LaCoO3/LSAT and LaCoO3/STO films, while LaCoO3/LAO films show weak ferromagnetism behavior. Meanwhile, LaCoO2.67 films exhibit antiferromagnetic behavior. An unexpected low-temperature ferromagnetism phenomenon with a Curie temperature of ~83 K and a saturation magnetization of ~1.2 μB/Co was discovered in15-nm-thick LaCoO2.5/LSAT thin films, which is probably related to the interface CoO6 octahedral rotation pattern change. Meanwhile, the observed ferromagnetism gradually disappears as the thickness of the film increases, indicating a tensile strain relaxation. 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 super-exchange effect between Co2+ (HS), Co2+ (LS), and Co2+ (HS) produced a low-temperature ferromagnetic behavior. However, compressive-strained LaCoO2.5 film on LaAlO3 substrate shows normal anti-ferromagnetism behavior. These results demonstrate both oxygen vacancies and tensile strain are correlated with the emergent magnetic properties in epitaxial LaCoO3-x films and provides a new perspective to regulate the magnetic properties of transition oxide thin films. |
