Thermal expansion and thermodynamic characterization of antiferromagnetic phase transition in elemental α ‐Mn

High‐resolution measurements of thermal expansion and specific heat have been performed on α ‐Mn. An analysis of these thermodynamic properties, with particular emphasis on their behavior in the temperature region near the Néel temperature, T N = 101.4(2) K, suggests that the antiferromagnetic phase transition is continuous (second order within the Ehrenfest classification scheme). The thermal expansion for T ≲ T N is negative, which is probably related to the volume dependence of the magnetic exchange interactions. This is manifested in the negative pressure derivative d T N / d P and may also be related to the anomalously low reported values of the bulk modulus for α ‐Mn. Large, negative values of the bulk Grüneisen function, γ G , for T < 75 K are comparable to those of antiferromagnetic Cr. In each case, the magnetic contribution to γ G dominates for T ≤ T N .