Magnetic excitations and anomalous spin wave broadening in multiferroic FeV2O4

TL;DR

This study investigates magnetic excitations and spin wave broadening in FeV2O4, revealing the roles of Fe2+ and V3+ ions, and identifies anomalous broadening linked to V3+ spin fluctuations and magnon-phonon coupling.

Contribution

It provides new insights into the distinct roles of Fe2+ and V3+ in magnetic excitations and uncovers the origin of anomalous spin wave broadening in FeV2O4.

Findings

High-energy gap due to Fe2+ spin-orbit coupling

No gap change from V3+ orbital ordering

V3+ spin fluctuations cause spin wave broadening

Abstract

We report on the different roles of two orbital-active Fe$^{2+}$ at the A site and V$^{3+}$ at the B site in the magnetic excitations and on the anomalous spin wave broadening in FeV$_{2}$O$_{4}$. FeV$_{2}$O$_{4}$ exhibits three structural transitions and successive paramagnetic (PM)-collinear ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI) transitions. The high-temperature tetragonal/PM -orthorhombic/CFI transition is accompanied by the appearance of an energy gap with a high magnitude in the magnetic excitations due to strong spin-orbit coupling induced anisotropy at the Fe$^{2+}$ site. While there is no measurable increase in the energy gap from the orbital ordering of V$^{3+}$ at the orthorhombic/CFI-tetragonal/NCFI transition, anomalous spin wave broadening is observed in the orthorhombic/CFI state due to V$^{3+}$ spin fluctuations at the B site. The spin wave broadening is also observed at the zone boundary without softening, which is discussed in terms of magnon-phonon coupling.