Tricritical Lines in Metamagnets

Abstract

Measurements of the magnetization of Fe${\mathrm{Br}}_2$ and Fe${\mathrm{Cl}}_2$ as a function of magnetic field, temperature, and hydrostatic pressure establish lines of tricritical points $T_{3c}$ with slopes $\frac{{\left(T_{3c}\right)}^{-1\mathrm{}}d{T}_{3c}}{\mathrm{dP}}=-0.025, +0.021, \mathrm{and} +0.040\mathrm{}$ ${\mathrm{kbar}}^{-1\mathrm{}}$ for the low- and high-pressure phases of Fe${\mathrm{Cl}}_2$ and for Fe${\mathrm{Br}}_2$, respectively. The variation of the tricritical transition with pressure should provide sensitive tests of theories relating interaction constants in the Hamiltonian to tricritical behavior in magnetic systems.