# Strain-gradient-induced magnetic anisotropy in straight-stripe mixed-phase bismuth ferrites: An insight into flexomagnetic phenomenon

## TL;DR

This study reveals how strain gradients in mixed-phase bismuth ferrites can control antiferromagnetic spin orientations, enabling electric-field-induced spin reorientation at room temperature through flexomagnetic effects.

## Contribution

It demonstrates the correlation between strain gradients and antiferromagnetic spin axes, providing a physical understanding and a pathway for electric control of magnetic states in multiferroic materials.

## Key findings

- Strain gradient induces magnetic anisotropy energy of about 5×10^{-12} eV·m per Fe ion.
- Electric-field-induced 90° spin rotation achieved at room temperature.
- Correlation established between mixed-phase boundary and in-plane antiferromagnetic spin axis.

## Abstract

Implementation of antiferromagnetic compounds as active elements in spintronics has been hindered by their insensitive nature against external perturbations which causes difficulties in switching among different antiferromagnetic spin configurations. Electrically-controllable strain gradient can become a key parameter to tune the antiferromagnetic states of multiferroic materials. We have discovered a correlation between an electrically-written straight-stripe mixed-phase boundary and an in-plane antiferromagnetic spin axis in highly-elongated La-5%-doped BiFeO$_{3}$ thin films by performing polarization-dependent photoemission electron microscopy in conjunction with cluster model calculations. Model Hamiltonian calculation for the single-ion anisotropy including the spin-orbit interaction has been performed to figure out the physical origin of the link between the strain gradient present in the mixed phase area and its antiferromagnetic spin axis. Our findings enable estimation of the strain-gradient-induced magnetic anisotropy energy per Fe ion at around 5$\times$10$^{-12}$ eV m, and provide a new pathway towards an electric-field-induced 90$^{\circ}$ rotation of antiferromagnetic spin axis at room temperature by flexomagnetism.

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Source: https://tomesphere.com/paper/1704.06627