Magnetic properties ofMn3O4and a solution of the canted-spin problem

Abstract

The temperature-dependent studies of the low-field magnetization $M$, the paramagnetic susceptibility $\chi$, and the electron-spin-resonance (ESR) parameters (linewidth $\Delta H$ and resonance field $H_r$) of a polycrystalline natural sample of the ferrimagnet hausmannite (${\mathrm{Mn}}_3$ ${\mathrm{O}}_4$) are reported. Since earlier attempts to fit $\chi$ and the canted-spin structure of ${\mathrm{Mn}}_3$ ${\mathrm{O}}_4$ occurring below its $T_C\simeq 42$ K with the use of Lotgering's model have been unsuccessful, special attention has been given to this problem. With the use of an extended Lotgering model, which is equivalent to Néel's two-sublattice model, a set of molecular-field constants, viz. ${\lambda }_{\mathrm{AB}}=54.3\mathrm{}$, ${\lambda }_{\mathrm{BB}}=78.9\mathrm{}$, and ${\lambda }_{\mathrm{AA}}=26.0\mathrm{}$, has been obtained from the fit of $\chi$ between 45 and 297 K. With these constants, the calculated values for the canting angle of the $B$ sublattices, the Curie temperature $T_C$, and the asymptotic Curie-Weiss temperature $T_a$ agree well with the experimental values for these parameters. The $M-\mathrm{vs}-T$ data yield anomalies at $T_C$ and 39 K, whereas $H_r$ and $\Delta H$ have anomalous changes at $T_C$, 39 K, and near 32 K. The anomalies near 39 and 32 K are indicative of the known spin reorientation transitions at these temperatures in ${\mathrm{Mn}}_3$ ${\mathrm{O}}_4$. The ESR parameters indicate a spin-only $g$ value for ${\mathrm{Mn}}^{3+}$ ions at the $B$ sites of ${\mathrm{Mn}}_3$ ${\mathrm{O}}_4$.