Anomalies in Thermal Expansion and Heat Capacity of Ferromagnets

Polymorphic transformations (PT) f.c.c. → h.c.p. in Co are investigated on the basis of Born's thermodynamic theory. The spontaneous deformation u23 is the PT parameter; the volume exchange ω is the additional variable. The PT problem is reduced to Landau's theory with the variable u23. The elastic moduli in this case are: (C11 – C12) → 0 and C44(T) = −C44(T) in the point T = T00 (T00 is the point of the instability). The maxima of the thermal expansion coefficient (TEC) and the elastic moduli as functions of T are calculated in the case of the first‐order PT. TEC anomalies are calculated by the method of near the orientational phase transition (OPT) point in Co and Ni. TEC is measured by the method of the continual T‐excchange. Anomalies of the TEC are found in the region of the PT in Co and near OPT in Co and Ni (near 500 K). The TEC quantities are in accord with the theoretical estimations. The TEC peak in the PT region permits to find the parameters of anharmonicity. [Russian Text Ignored].