Temperature dependences of strain and charge effects modulated by electric fields in a STO/Fe₃O₄/Au/PZT multiferroic heterostructure

The temperature dependences of pure strain, pure charge, and their coexisting effects are simultaneously investigated with electric fields applied at three individual positions of an unconventional SrTiO₃(STO)/Fe₃O₄/Au/PbZr_0.52Ti_0.48O₃(PZT) multiferroic heterostructure. As the temperature drops, for all situations, the magnetization anomalously decreases with an increment in coercivity. The phenomenon is ascribed to the Verwey transition present in the Fe₃O₄. However, the magnetic responses to electric field are different for the pure strain and pure charge effects. The maximum strain- and charge-mediated coupling coefficients are 10.51 and 1.26 Oe · cm kV⁻¹, respectively, both obtained near the Verwey transition temperature. The combination of the two coupling mechanisms leads to the nonequivalent shift of the Verwey transition temperature under reversed electric fields, which can be explained by their interaction. It is also found that large magnetoelectric couplings can be realized over a broad temperature range when the strain and charge effects simultaneously appear. (paper)