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.