Temperature dependence of the elastic constants in α-iron single crystals: relationship to spin order and diffusion anomalies

The temperature dependence of the elastic constants of single-crystal iron has been measured from 25 to 900°C. A nonlinearity of temperature dependence for the three measured independent constants is associated with the degree of ferromagnetic ordering. The c′ = (C11−c12)/2 is nonlinear in the paramagnetic region as well. A marked difference in sensitivity to spin order between the c′ and c44 shear constants implies that the exchange interaction is, for the most part, between second, not first nearest neighbors. The nonlinearity in temperature dependence of the elastic constants is used to account for (by means of the Zener theory) the nonlinear Arrhenius plots for the diffusion of carbon and self-diffusion in α-iron.