The strain induced magnetic and anisotropic variations of LaCoO3 thin films

Abstract

The emergence of ferromagnetism in tensile strained LaCoO3 (LCO) films is still being researched due to the lack of any uniform explanation. Herein, the magnetic anisotropy and the precise ratio of Co2+ ions in LCO films growth on different substrates are reported. The emergence of ferromagnetic state can be observed irrespective of the tensile or compressive strain on the LCO films. A small magnetization along the out-of-plane easy axis is exhibited in the LCO film under compressive strain. The maximum magnetization (1.11 μB/u.c.) is observed in the LCO film over tensile strained LSAT substrate along the in-plane easy axis, which is around four times compared to the magnetization of LCO film on compressive strain. In addition, the exact percentage of Co2+ ions in different LCO films deviated from 12.8% to 10.6% as the strain changed from tensile to compressive. This little variation has a relatively weak effect on the hugely different magnetization of LCO films. Subsequently, the magnetization of LCO film grown on STO buffer layer has a great increase compared to the film direct on LAO substrate. All these results support the proposition that the tensile strain should induce more IS (t2g5eg1) or HS (t2g4eg2) spin states of Co3+ ions, which plays the key role for enhancement of ferromagnetism.