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 $\frac{{({T}_{3c})}^{\ensuremath{-}1}d{T}_{3c}}{\mathrm{dP}}=\ensuremath{-}0.025, +0.021, \mathrm{and} +0.040$ ${\mathrm{kbar}}^{\ensuremath{-}1}$ 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.