Spin-flop bicritical point in MnF2

From measurements of the susceptibility and rf absorption, we have determined the phase diagram of MnF2 near its bicritical point which is located at TB=64.792±0.001 K and HB=118.353±0.01 kOe. Alignment of easy axis and applied field was achieved within 2×10-6 rad. We find, quite accurately, an anisotropy crossover exponent φ=1.279±0.031, in good agreement with renormalization-group predictions for an n=3 component system. However, the less exactly determined amplitude ratio Q=1.56±0.35 of the two phase boundaries to the paramagnetic state, lies between that predicted for n=3 and that for n=2. The nonuniversal slope q of the t=0 scaling axis is q=(1.19±0.15)×10-6 (kOe-2) and the amplitude w+ for the spin-flop to paramagnetic phase boundary is w+=(2.67±0.3)×106 (kOe2). © 1979 The American Physical Society.