To elucidate the change of interface magnetization with gate voltage, ferroelectric (FE) polarization (P) measurements are carried out, as shown in Fig. 2(a). The FE polarization saturates with gate voltage above 10 V (electric field of approximately 180kV/cm) or below -10V, indicating that all FE domains are aligned. The switching transition around U_g = ± 2V is not sharp, resulting from the variance in switching threshold of different FE domains. From the FE polarization measurement, we derive the change in magnetic contrast A as a function of P, as shown in Fig. 2(b), using the dependence of A on gate voltage U_g (Fig. 1(d)). The relationship between A and P exhibits a linear correlation, independently of the history of polarizing PZT layer, as the data with decreasing gate voltage (black) overlaps with the increasing one (red). The magnetic contrast A as a function of strain S is depicted in Fig. 2(c), which is derived from the relationship between strain and gate voltage in PZT thin films studied and using the dependence of A on gate voltage U_g (Fig. 1(d)). There is no clear correlation between interface magnetization and strain. Thus, the observed change of interface magnetization with gate voltage results from charge injection, the degree of which is estimated to be ± 0.231 electrons per Mn ion in the first unit cell layer at the interface.

Funding: DOE