Tuning magnetoelectricity in a mixed-anisotropy antiferromagnet

TL;DR

This study shows that replacing some Ni with Fe in LiNiPO4 enhances and unlocks magnetoelectric effects by lowering symmetry and introducing new couplings, advancing material control for electronic applications.

Contribution

The paper demonstrates how mixed-anisotropy in LiNi$_{1-x}$Fe$_x$PO$_4$ significantly enhances and enables new magnetoelectric couplings through symmetry lowering.

Findings

Magnetoelectric coupling is increased by two orders of magnitude.

Replacing Ni with Fe introduces symmetry-lowering effects.

New magnetoelectric couplings are unlocked in the mixed compound.

Abstract

Control of magnetization and electric polarization is attractive in relation to tailoring materials for data storage and devices such as sensors or antennae. In magnetoelectric materials, these degrees of freedom are closely coupled, allowing polarization to be controlled by a magnetic field, and magnetization by an electric field, but the magnitude of the effect remains a challenge in the case of single-phase magnetoelectrics for application. We demonstrate that the magnetoelectric properties of the mixed-anisotropy antiferromagnet LiNi$_{1-x}$Fe$_x$PO$_4$ are profoundly affected by replacing a fraction of the Ni$^{2+}$ ions with Fe$^{2+}$ on the transition metal site. This introduces random site-dependent single-ion anisotropy energies and causes a lowering of the magnetic symmetry of the system. In turn, magnetoelectric couplings that are symmetry-forbidden in the parent compounds, LiNiPO$_4$ and LiFePO$_4$, are unlocked and the dominant coupling is enhanced by two orders of magnitude. Our results demonstrate the potential of mixed-anisotropy magnets for tuning magnetoelectric properties.