A calculation of elastic constants of ferromagnetic iron at finite temperatures

The temperature dependence of the elastic constants C'=1/2(C11-C12),C44 and B of BCC iron is calculated within the tight-binding approximation using the single-site spin-fluctuation theory of band magnetism. The theory reproduces the observed anomalous 'softening' of the tetragonal shear constant C', relating it to the contribution of the eg orbitals. The negative slope with temperature of the trigonal shear constant C44 and bulk modulus B is shown to arise from the lattice expansion. The influence of magnetic moments on the elastic constants of ferromagnetic and antiferromagnetic, BCC transition metals is discussed in general.