Nontrivial temperature dependence of magnetic anisotropy in multiferroics Ba$_2$MnGe$_2$O$_7$

TL;DR

This study investigates the unusual temperature dependence of magnetic anisotropy in the multiferroic Ba$_2$MnGe$_2$O$_7$, revealing that spin nematic interactions linked to electric polarization influence anisotropy gaps.

Contribution

It demonstrates that the anisotropy gap scales with electric polarization and attributes this to temperature-induced changes in spin nematic interactions and orbital hybridization.

Findings

Anisotropy gap scales with electric polarization.

Spin nematic interaction causes easy-axis anisotropy.

Temperature affects orbital hybridization, altering spin interactions.

Abstract

We measured the temperature dependences of the static magnetization and the spin excitation in a square-lattice multiferroics Ba$_2$MnGe$_2$O$_7$. An anisotropy gap of the observed low energy mode is scaled by electric polarization rather than a power of sublattice moment. Spin nematic interaction in effective spin Hamiltonian, which is equivalent to interaction of electric polarization, is responsible for the easy-axis anisotropy. The nontrivial behavior of the anisotropy gap can be rationalized as change of the hybridized $d$-$p$ orbital with temperature, leading to the temperature dependence of the spin nematic interaction.