Electric-field-induced magnetic easy-axis reorientation in ferromagnetic/ferroelectric layered heterostructures

A phenomenological model is presented for the electric-field-induced reorientation of magnetic easy axis in ferromagnetic (FM)/ferroelectric (FE) layered heterostructures, where the FM layers include either polycrystalline or (001) preferentially oriented films of widely used Fe, CoFe2O4 (CFO), Ni, and Fe3O4. The magnetic easy axes could rotate within the film plane at relatively low applied electric fields in CFO, Ni, and Fe3O4 films. As the applied electric field increases, the easy axes tend to switch from an in-plane direction to an out-of-plane one in CFO and Ni films. Such electric-field-induced easy-axis reorientations (EARs) can be abrupt and gradual, defined as first-order and second-order transitions, respectively. The influences of residual strain, different electric-field orientations, and nonlinear strain vs electric-field behavior of the FE substrates, on the EARs are also addressed.