Quantitative analysis of magnetization reversal in Ni thin films on unpoled and poled (011) [PbMg1/3Nb2/3O3](0.68)-[PbTiO3](0.32) piezoelectric substrates

Abstract

The field angle dependence of the magnetization reversal in 20 nm thick polycrystalline Ni films grown on piezoelectric (0 1 1) [PbMg1/3Nb2/3O3](0.68)-[PbTiO3](0.32) (PMN-PT) substrates is analysed quantitatively to study the magnetic anisotropy induced in the film by poling the piezosubstrate. While the PMN-PT is in the unpoled state, the magnetization reversal is almost isotropic as expected from the polycrystalline nature of the film and corresponding to an orientation ratio (OR) of 1.2. The orientation ratio is obtained by fitting the angular dependence of normalized remanent magnetization to an adapted Stoner-Wohlfarth relation. Upon poling the piezosubstrate, a strong uniaxial anisotropy, whose hard axis is oriented along the [1 0 0] direction of the PMN-PT, is induced, yielding an OR of 3.1. The angular dependence of the coercivity for the poled state is found to consist of a strong increase for increasing field angles away from the easy axis direction and of a sharp decrease for angles close to the hard direction. It is best described by a two-phase model, implying that the magnetization reversal is determined by both, coherent rotation of the magnetic moments, according to the Stoner-Wohlfarth model, and the gradual displacement of the domain walls in obedience to the Kondorsky model.