Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that $\mathrm{FeM}{\mathrm{n}}_2{\mathrm{O}}_4$ undergoes one structural and two magnetic transitions. The structural transition occurs at $T_s\sim 595\mathrm{K}$ from cubic at high temperatures to tetragonal at low temperatures. Two magnetic transitions are ferrimagnetic at $T_{\mathrm{FI}-1}\sim 373\mathrm{K}$ and $T_{\mathrm{FI}-2}\sim 50\mathrm{K}$, respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to the low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.

• Received 6 September 2017
• Revised 21 November 2017

DOI:https://doi.org/10.1103/PhysRevB.97.024410