We report on the different roles of two orbital-active ${\mathrm{Fe}}^{2+}$ at the $A$ site and ${\mathrm{V}}^{3+}$ at the $B$ site in the magnetic excitations and on the anomalous spin-wave broadening in $\mathrm{Fe}{\mathrm{V}}_2{\mathrm{O}}_4$. $\mathrm{Fe}{\mathrm{V}}_2{\mathrm{O}}_4$ exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the ${\mathrm{Fe}}^{2+}$ site. While there is no measurable increase in the energy gap from the orbital ordering of ${\mathrm{V}}^{3+}$ at the orthorhombic/CFI–tetragonal/NCFI transition, anomalous spin-wave broadening is observed in the orthorhombic/CFI state due to ${\mathrm{V}}^{3+}$ spin fluctuations at the $B$ site. The spin-wave broadening is also observed at the zone boundary without softening in the NCFI/ferroelectric phase, which is discussed in terms of magnon-phonon coupling. Our study also indicates that the ${\mathrm{Fe}}^{2+}$ spins without the frustration at the $A$ site may not play an important role in inducing ferroelectricity in the tetragonal/NCFI phase of $\mathrm{Fe}{\mathrm{V}}_2{\mathrm{O}}_4$.

• Received 21 April 2014
• Revised 3 June 2014

DOI:https://doi.org/10.1103/PhysRevB.89.224416