Microscopic Origin of Polarization-Controlled Magnetization Switching in FePt/BaTiO$_3$

TL;DR

The paper tackles voltage-controlled magnetization in FePt/BaTiO$_3$ by combining first-principles calculations with a strain-polarization framework. It identifies an interfacial orbital-reconstruction mechanism that yields a large magnetoelectric coefficient $α_I$ and reveals a strain-induced spin-reorientation around $η \approx 2\%$ driven by competition between uniaxial interfacial anisotropy and magnetoelastic energy, all modulated by interfacial Pt–d orbital SOC. The work provides microscopic insight into strain-engineered magnetoelectricity and outlines a concrete design path for ultra-low-power voltage-controlled magnetic memory. The findings map a route to integrate polarization control with SOC-enabled interfacial physics in FePt/BTO heterostructures for spintronic applications, highlighting a practical pathway for low-power devices.

Abstract

Electric-field driven magnetization switching in FePt/BaTiO$_3$ (001) is demonstrated through first-principles calculations. The magnetic easy axis of FePt layer undergoes a transition from in-plane to perpendicular direction upon ferroelectric polarization reversal, a process sensitively controlled by epitaxial strain with threshold strain strain($η$) $η\approx\%$. At this phenomena, a large interfacial magnetoelectric coupling ($α_I = 3.6 \times 10^{-10}$ G$\cdot$cm$^2$/V) is responsible, stemming from the orbital reconstruction. In particular, the redistribution of Pt-$d$ orbital occupancy alters spin-orbit coupling, thereby tuning the competition between magnetic anisotropy ($K_i$) and magnetoelastic energy ($b_1$). Our work clarifies the fundamental physics of strain-engineered magnetoelectricity and suggests a concrete pathway for designing ultra-low-power voltage-controlled magnetic memory.

Figures (5)

• Figure 1: Schematics of the FePt/BaTiO$_3$(001) heterostructure: (a) $P_+$ and (b) $P_-$, as indicated by black solid arrows. The shaded central panel highlights the regions of the surface (S), interface (I), and BaTiO$_3$ layer. Grey, green, blue, cyan, and red spheres represent Pt, Fe, Ba, Ti, and O atoms, respectively. Dotted arrows within the octahedra indicate the local displacements of atoms.
• Figure 2: (a) Relative displacement of cations (M = Ba and Ti) with respect to O plane. Filled circles and upper(lower) triangles are for 0$\%$ and +2(-2)$\%$ strains. Shaded region corresponds to the interface (I) and BaTiO$_3$ regions. (b) Magnetic moment ($\mu_B$) of interface Fe, Pt, and Ti atoms as a function of strain. Broken y-axis is separate Fe from Pt and Ti with colored shades. Circle, triangle, and square represent Fe, Pt, and Ti atoms, respectively. Red and blue denote $P_+$ and $P_-$, respectively.
• Figure 3: Layer-resolved density of states (LDOS) for the interfacial (I) region: (a) and (b) Pt(I), (c) and (d) Fe(I), (e) and (f) TiO$_2$(I), and for a few inner layers: (g) and (h) TiO$_2$(I1), (i) and (j) TiO$_2$(I2), for $P_+$ (left panels) and $P_-$ (right panels). The filled grey region represents the LDOS at zero strain. The dashed blue and solid pink lines represent the DOS at +2$\%$ and -2$\%$ strain, respectively. The vertical solid line indicates the Fermi level ($E_F$), which is set to zero.
• Figure 4: Magnetic anisotropy energy ($E_{MA}$) of FePt/BaTiO$_3$ heterostructure as a function of strain ($\eta$). Red and blue color denote $E_{MA}$ for $P_+$ and $P_-$, respectively. Shaded region indicates critical strain ($\eta_c$) at which magnetic anisotropy energy shifts from perpendicular to in-plane direction. Layer-resolved $E_{MA}$ at (b) $\eta=0\%$ and (c) $\eta=2\%$ for polarization direction $P_+$ (red) and $P_-$ (blue), respectively.
• Figure 5: Interfacial Pt d-orbital projected difference in SOC energies ($\Delta$SOC) between in-plane and perpendicular magnetization for polarization $P_+$ at (a) $\eta$ = 0$\%$ and (b) $\eta$ = 2$\%$, where yellow, red, and blue bars represent $\Delta$SOC $>$ 0, $<$ 0, and = 0, respectively. Orbital-resolved band structure for the majority spin (upper panel) and the minority spin (lower panel) at (c) $\eta$ = 0$\%$ and (d) $\eta$ = 2$\%$. Bands with yellow, magenta, and green denote $xz$, $yz$, and $z^2$ orbitals, respectively. The size of the symbols represents the weight of d-orbitals.