The manipulation of magnetic coercive field and orientation of magnetic anisotropy via electric fields

Abstract

We report the effects of the electric field on the magnetic coercive field (Hc) and uniaxial magnetic anisotropy (UMA) orientation of polycrystalline Ni film grown on an unpoled (0 1 1) [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x (PMN-PT) single crystal substrate. Under various electric fields, normalized magnetic hysteresis loops of Ni films change in width; this represents the change of coercive field (ΔHc). Loop shapes are found to depend on the angle between the magnetic field and the sample, where changes in the shape reveal a small rotation of UMA. All these changes show that the magnetic properties vary periodically with a periodic electric field, by strain-mediated magnetoelectric coupling in the Ni/Ag/PMN-PT/Ag heterostructure. The poled PMN-PT produces strains under electric fields in the range of −4.2 kV cm−1 ⩽ E ⩽ 4.2 kV cm−1, then transfers it to Ni films resulting in changes to its Hc and UMA. The curves of the in-plane Hc and strain, at two mutually orthogonal directions, represent butterfly patterns versus the applied electric field. In addition, the changes observed in both the Hc and strain show asymmetric features in two orthogonal directions, which results in a small rotation angle of the UMA of Ni as the electric field decreases. The effective manipulation of magnitude and orientation of magnetic anisotropy via electric fields in ferromagnetic/ferroelectric (FM/FE) heterostructures is an important step towards controlling the magnetic tunnel junctions.