Liquid-Vapor-Like Critical Points in Anisotropic Ferrimagnets

A magnetic critical phase transition which involves no change in symmetry is described theoretically. In the example, ${\mathrm{Yb}}_6$ ${\mathrm{Fe}}_{10}$ ${\mathrm{O}}_{24}$ with applied field along [100], a critical point is predicted at $T^c=7.51\mathrm{}°$K and $H^c=43\mathrm{}640$ Oe. There is a large associated anomaly in $C_H: C_H(H=H^c)\approx 0.3{(T-T^c)}^{\frac{1}{\delta }-1\mathrm{}}R$ ${\mathrm{mole}}^{-1\mathrm{}}$, where $\delta$ should realize the classical value 3.