Ferroelectric Control of Anisotropic Magnetoresistance in Ultrathin Sr2IrO4 Films toward 2D Metallic Limit

The Ruddlesden-Popper 5d iridate Sr₂IrO₄ is an antiferromagnetic Mott insulator with the electronic, magnetic, and structural properties highly intertwined. Voltage control of its magnetic state is of intense fundmenatal and technological interest but remains to be demonstrated. Here, the tuning of magnetotransport properties in 5.2 nm Sr₂IrO₄ via interfacial ferroelectric PbZr_0.2Ti_0.8O₃ is reported. The conductance of the epitaxial PbZr_0.2Ti_0.8O₃/Sr₂IrO₄ heterostructure exhibits ln(T) behavior that is characteristic of 2D correlated metal, in sharp contrast to the thermally activated behavior followed by 3D variable range hopping observed in single-layer Sr₂IrO₄ films. Switching PbZr_0.2Ti_0.8O₃ polarization induces nonvolatile, reversible resistance modulation in Sr₂IrO₄. At low temperatures, the in-plane magnetoresisance in the heterostructure transitions from positive to negative at high magnetic fields, opposite to the field dependence in single-layer Sr₂IrO₄. In the polarization down state, the out-of-plane anisotropic magnetoresistance R_AMR exhibits sinusoidal angular dependence, with a 90° phase shift below 20 K. For the polarization up state, unusual multi-level resistance pinning appears in R_AMR below 30 K, pointing to enhanced magnetocrystalline anisotropy. The work sheds new light on the intriguing interplay of interface lattice coupling, charge doping, magnetoelastic effect, and possible incipient ferromagnetism in Sr₂IrO₄, facilitating the functional design of its electronic and material properties.