Spin-flop bicritical point in MnF2

Abstract

From measurements of the susceptibility and rf absorption, we have determined the phase diagram of Mn${\mathrm{F}}_2$ near its bicritical point which is located at $T_B=64.792\mathrm{}\pm 0.001$ K and $H_B=118.353\mathrm{}\pm 0.01$ kOe. Alignment of easy axis and applied field was achieved within 2×${10}^{-6\mathrm{}}$ rad. We find, quite accurately, an anisotropy crossover exponent $\phi =1.279\mathrm{}\pm 0.031$, in good agreement with renormalization-group predictions for an $n=3\mathrm{}$ component system. However, the less exactly determined amplitude ratio $Q=1.56\mathrm{}\pm 0.35$ of the two phase boundaries to the paramagnetic state, lies between that predicted for $n=3\mathrm{}$ and that for $n=2\mathrm{}$. The nonuniversal slope $q$ of the $\tilde{t}=0\mathrm{}$ scaling axis is $q=(1.19\mathrm{}\pm 0.15)\times {10}^{-6\mathrm{}}$ (k${\mathrm{Oe}}^{-2\mathrm{}}$) and the amplitude $w_{+}$ for the spin-flop to paramagnetic phase boundary is $w_{+}=(2.67\mathrm{}\pm 0.3)\times {10}^6$ (k${\mathrm{Oe}}^2$).