The magnetic and structural properties of single-crystal ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{\mathrm{V}}_2{\mathrm{O}}_4$ samples have been investigated by performing specific heat, susceptibility, neutron diffraction, and x-ray diffraction measurements. As the orbital-active ${\mathrm{Fe}}^{2+}$ ions with larger ionic size are gradually substituted by the orbital-inactive ${\mathrm{Co}}^{2+}$ 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 ${\mathrm{Fe}}^{2+}$ ions on the A sites and the orbital ordering and electronic itinerancy of the ${\mathrm{V}}^{3+}$ 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 ${\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{V}}_2{\mathrm{O}}_4$ and ${\mathrm{Mn}}_{1-x}{\mathrm{Co}}_x{\mathrm{V}}_2{\mathrm{O}}_4$ to emphasize several distinct features.

• Received 14 April 2015

DOI:https://doi.org/10.1103/PhysRevB.92.134410