Experimental observation of crossover phenomena in the specific heat of MnF2

Abstract
High-precision measurements of the specific heat Cp of MnF2 near its Neel temperature, TN have been performed. It is shown for 10-2N mod -1 that magnetic specific heat obeys a power-law singularity with exponents characteristic of the three-dimensional Heisenberg model, that is, alpha = alpha '=-0.103. As one approaches TN, a crossover to dipolar-dominated Ising nature can be clearly observed. Asymmetric behaviour of the critical divergence in the vicinity of TN can be also well explained by the existing numerical values of the magnetic anisotropy.