Low-Temperature Magnetization of Mn${\left(\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\right)}_2$·4${\mathrm{H}}_2$O

Magnetization isotherms in fields up to 15 kOe have been measured at temperatures between 1.5 and 4.2°K for monoclinic single crystals of manganous acetate tetrahydrate. Continuous, quasistatic isotherms were obtained with the field along three orthogonal axes $a$, $b$, and $c^{\prime }$. Below the zero-field transition temperature of 3.18°K, the isotherms for $\mathbf{H}\parallel a$ exhibit an abrupt, perhaps discontinuous, rise at field <5 Oe, and saturate at about $\left(\frac{5}{3}\right){\mu }_B·\left({\mathrm{Mn}}^{++}\mathrm{ion}\right)$. With $\mathbf{H}\parallel b$ and $\mathbf{H}\parallel c^{\prime }$, essentially the same saturation moment was found, but no threshold effect. The magnitude of the saturation moment is consistent with a ferrimagnetic arrangement of ${\mathrm{Mn}}^{++}$ moments ($S=\frac{5}{2}$, $g=2\mathrm{}$) on two kinds of inequivalent lattice sites in the ratio 2:1. The threshold effect suggests, however, that the system combines metamagnetic properties with those of ferrimagnetism.