Weak ferromagnetism and internal magnetoelectric effect in LiFeP$_2$O$_7$

TL;DR

This study reveals that LiFeP$_2$O$_7$ exhibits weak ferromagnetism and a strong internal magnetoelectric effect, with magnetic order strongly coupled to electric polarization and lattice, demonstrated through magnetic, thermodynamic, and pyroelectric measurements.

Contribution

It provides detailed insights into the magnetoelectric coupling and spin-lattice interactions in LiFeP$_2$O$_7$, highlighting its weak ferromagnetism and strong internal magnetoelectric effects.

Findings

Magnetic order below T_N is a canted antiferromagnet with weak ferromagnetism.

Strong internal magnetoelectric interaction causes a polarization decrease at T_N.

Large uniaxial magnetoelastic response indicates strong spin-lattice coupling.

Abstract

The magnetic, thermodynamic, and pyroelectric properties of LiFeP$_2$O$_7$ single crystals are investigated with emphasis on the magnetoelectric interaction of the electrical polarization with the magnetic order parameter. The magnetic order below T$_N\simeq$ 27 K is found to be a canted antiferromagnet with a weak ferromagnetic component along the $b-$axis. A sharp peak of the pyroelectric current at T$_N$ proves the strong internal magnetoelectric interaction resulting in a sizable polarization decrease at the onset of magnetic order. The magnetoelectric effect in external magnetic fields combines a linear and a quadratic field dependence below T$_N$. Thermal expansion data show a large uniaxial magnetoelastic response and prove the existence of strong spin lattice coupling. LiFeP$_2$O$_7$ is a polar compound with a strong interaction of the magnetic order parameter with the electric polarization and the lattice.