Manipulation of magnetic properties by electric field in epitaxial Fe/BTO/Nb:STO film

We demonstrate reversible electric-field control of the coercive field of a 10 nm epitaxial Fe film by switching the polarization of an underlying 41 nm BaTiO₃ (BTO) layer grown on Nb:SrTiO₃ (Nb:STO) substrates. High-quality epitaxy of the Fe(10 nm)/BTO(41 nm)/Nb:STO stack was achieved with Fe[100]‖BTO[110] and Fe[110]‖BTO[100] orientation relationships. As-grown, the Fe film exhibits uniaxial magnetic anisotropy with its easy axis along the Fe[100] direction. Under out-of-plane electric fields up to ±6 V, the Fe coercive field is modulated by ≈ 5–10 Oe. The voltage dependence of the coercive field is consistent with ferroelectric polarization switching in the BTO layer. This observation provides clear evidence of robust interfacial magnetoelectric coupling in Fe/BTO heterostructures. We propose that polarization-induced atomic displacements or distinct strain induced from out-of-plane and in-plane domains in BTO transmit anisotropic strain across the interface to the Fe film, thereby tuning its coercivity. We note that this strain-mediated mechanism remains a hypothesis: our PFM and MOKE data establish a clear correlation between ferroelectric switching and H_C shifts but do not directly probe the interfacial atomic structure. Direct confirmation will require future atomic-scale studies. These results highlight epitaxial Fe/BTO/Nb:STO heterostructures as promising platforms for voltage-tunable spintronic devices.