Neutron diffraction study on exotic magnetic properties of Mn substituted spinel cobalt chromite

We report the evolution of temperature and magnetic field dependent magnetic properties of Mn substituted spinel cobalt chromite ${\mathrm{Co}\left({Cr}_{0.7}{Mn}_{0.3}\right)}_2{O}_4$ compound. It is observed that 30$\%$ 'Mn' substitution for Cr-site in ${CoCr}_2{O}_4$ results in magnetic compensation and huge reversal of temperature dependent magnetization below compensation temperature, $T_{comp}$$\sim$83 K under low applied fields which was absent in the parent compound ${CoCr}_2{O}_4$. For large applied fields magnetization reversal disappears but ends in field induced transition across $T_{comp}$. Magnetic hysteresis loops exhibit gigantic coercivity at 3 K, and dramatically drops on increasing temperature. The exchange-bias-like behavior is observed below 10 K and as well as in the vicinity of compensation point, $T_{comp}$($\sim$83 K). Low temperature neutron powder diffraction (NPD) experiment shows the possible magnetic structure and ordering in ${\mathrm{Co}\left({Cr}_{0.7}{Mn}_{0.3}\right)}_2{O}_4$. Non-monotonic change in bond lengths and bond angles around the compensation temperature ($T_{comp}$) revealed that there is a correlation between crystal and magnetic structure. Possible origin behind such exotic magnetic properties has been discussed in detail in the paper.