CRITICAL EXPONENTS OF EUTE FROM SPECIFIC-HEAT AND THERMAL-EXPANSION MEASUREMENTS

The antiferromagnet EuTe shows a distinct cross-over behavior in the specific heat C when approaching the Neel temperature T(N) = 9.8 K. For \t\ = \(T - T(N))/T(N) \ > 0.01 the critical exponent of the specific heat, C alpha \t\-alpha, is almost zero, alpha = 0.0085 +/- 0.003. Closer to T(N), for 0.0015 < \t\ < 0.01, C exhibits a different behavior with a surprisingly large positive alpha = 0.38 +/- 0.1, considerably exceeding even the d = 3 Ising exponent alpha = 0.11. Measurements of the thermal expansion yield essentially the same cross-over behavior with alpha = 0.002 +/- 0.01 for \t\ > 0.01 and alpha = 0.43 +/- 0.2 for 0.001 < \t\ < 0.03. Although EuTe is considered to be a Heisenberg antiferromagnet, some anisotropy might be expected because of dipolar interactions, possibly causing the observed cross-over.