Comment on the Stress-Induced Tricritical Point in MnO

Abstract

Bloch et al. have observed that application of a [111] stress causes the first-order transition in MnO to become second order. We point out that the change of nature of the phase transition many be explained by noting that at zero stress the transition is described by an $n=8\mathrm{}$ vector model which has no stable fixed point, while for large enough stress the transition is described by an $n=2\mathrm{}$ model which has a stable fixed point. We suggest that a similar effect might be observed in U${\mathrm{O}}_2$, Cr, and Eu by applying a symmetry-breaking field, such as a nonisotropic stress or a magnetic field.