Dynamic observation of magnetoelectric coupling effect using magnetic force microscopy and Lorentz TEM*

Dynamic observation of the strain mediated magnetoelectric (ME) coupling effect was pursued by applying an external electric (E) field to a Fe$_{0.7}$Ga$_{0.3}$/BaTiO$_{3 }$(FeGa/BTO) TEM sample in the Lorentz imaging mode in a TEM. An epitaxial piezoelectric BTO layer followed by a polycrystalline magnetostrictive FeGa layer were synthesized by pulsed laser deposition and magnetron sputtering, respectively. The BTO film had Ps = 17 $\mu $C/cm$^{2 }$measured using SrRuO$_{3}$ (bottom) and FeGa (top) electrodes. The FeGa film showed strong magnetic anisotropy with in-plane easy axis. To apply an E field in-plane, FeGa was patterned on BTO using e-beam lithography. The change of magnetic domain structure was observed under an applied magnetic field in TEM. The ME effect was also investigated using MFM. After applying an E field (100 kV/cm) on the BTO layer, a reorientation of the magnetic moments in the FeGa layer along the E field direction was observed.