Using an ac calorimetric method, heat-capacity measurements were made for a "monodomain" and a "polydomain" sample. The former exhibited a clear critical behavior which was analyzed with an expression containing a critical-exponent term. The exponent has an Ising value within a standard deviation. On the other hand, the polydomain sample showed a smaller and different anomaly. Using a special sample-setting method, the above behaviors were verified directly by measuring the heat capacity under externally applied stress conditions. The differences in heat capacities observed leads us to imagine that crossover from Heisenberg to Ising behavior with external stress takes place due to the existence of the bicritical point. © 1977 The American Physical Society.