Mechanisms of dielectric anomalies in BaMnF4

The $b$-axis dielectric anomaly at the commensurate-incommensurate phase-transition temperature in BaMn${\mathrm{F}}_4$ has been calculated. Its shape and magnitude agree with the data of Samara and Richards. The $a$-axis anomaly below $T_N$ is also explained; its shape and magnitude are due to the canting of Mn spins. It is a first-order effect and ∼ ${10}^5$ larger than in Rado's second-order theory for ${\mathrm{Cr}}_2$ ${\mathrm{O}}_3$.