Electric-Field Effect on Magnetic Properties of FePt/PZN-PT Heterostructures

FePt films on PZN-PT single-crystal substrate, the ferromagnetic/piezoelectric (FM/PE) heterostructures, were fabricated by magnetron sputtering. The effects of the electric field on the coercivity and magnetization of the FePt at room temperature in FM/PE heterostructures were investigated. The as-grown FePt film showed an in-plane magnetic anisotropy. Upon applying an electric field, the out-of-plane magnetic loops of the heterostructure changed obviously, but the in-plane loops remained unchanged. When the applied E field increased from 0 to 5 kV/cm, the coercivity of out-of-plane increased from 4614 to 4907 Oe. The change of out-of-plane coercivity with different E field is consistent with the strain-electric-field loop of piezoelectric materials. Therefore, the increase of the coercivity can be attributed to that the electric-field-induced strain resulted in increased anisotropy normal to the film plane. The magnetization reversal process of easy direction was mainly due to domain wall motion, which may explain the invariability of the in-plane loops. Based on these results, it was believed that the electric-field-induced piezoelectric strain from the bottom PZN-PT substrate was effectively transferred to the top FePt layer.