Evolution of the magnetic and structural properties of Fe$_{1-x}$Co$_x$V$_2$O$_4$

TL;DR

This study explores how substituting Fe with Co in Fe$_{1-x}$Co$_x$V$_2$O$_4$ alters its magnetic and structural phases, revealing complex interactions between orbital, spin, and lattice degrees of freedom.

Contribution

It provides a detailed phase diagram of Fe$_{1-x}$Co$_x$V$_2$O$_4$ and compares it with related compounds, highlighting the effects of ionic size and electronic itinerancy.

Findings

Complex magnetic and structural phase diagram identified.

Orbital and spin interactions are influenced by Co substitution.

Distinct features compared to similar vanadate spinels.

Abstract

The magnetic and structural properties of single crystal Fe$_{1-x}$Co$_x$V$_2$O$_{4}$ samples have been investigated by performing specific heat, susceptibility, neutron diffraction, and X-ray diffraction measurements. As the orbital-active Fe$^{2+}$ ions with larger ionic size are gradually substituted by the orbital-inactive Co$^{2+}$ ions with smaller ionic size, the system approaches the itinerant electron limit with decreasing V-V distance. Then, various factors such as the Jahn-Teller distortion and the spin-orbital coupling of the Fe$^{2+}$ ions on the A sites and the orbital ordering and electronic itinerancy of the V$^{3+}$ ions on the B sites compete with each other to produce a complex magnetic and structural phase diagram. This phase diagram is compared to those of Fe$_{1-x}$Mn$_x$V$_2$O$_{4}$ and Mn$_{1-x}$Co$_x$V$_2$O$_{4}$ to emphasize several distinct features.