Voltage control of magnetism in Fe3-$x$GeTe2/In2Se3 van der Waals ferromagnetic/ferroelectric heterostructures

We investigate the voltage control of magnetism in a van der Waals (vdW) heterostructure device consisting of two distinct vdW materials, the ferromagnetic Fe3-$x$GeTe2 and the ferroelectric In2Se3. It is observed that gate voltages applied to the Fe3-$x$GeTe2/In2Se3 heterostructure device modulate the magnetic properties of Fe3-$x$GeTe2 with significant decrease in coercive field for both positive and negative voltages. Raman spectroscopy on the heterostructure device shows voltage-dependent increase in the in-plane In2Se3 and Fe3-$x$GeTe2 lattice constants for both voltage polarities. Thus, the voltage-dependent decrease in the Fe3-$x$GeTe2 coercive field, regardless of the gate voltage polarity, can be attributed to the presence of in-plane tensile strain. This is supported by density functional theory calculations showing tensile-strain-induced reduction of the magnetocrystalline anisotropy, which in turn decreases the coercive field. Our results demonstrate an effective method to realize low-power voltage-controlled vdW spintronic devices utilizing the magnetoelectric effect in vdW ferromagnetic/ferroelectric heterostructures.