Thermodynamic Properties of Sinusoidal Spin Density Waves by the Band Model

Abstract

The increase of the free energy density due to a given distribution of the antiferromagnetic magnetization 2µBn(r) is written as a function of temperature, magnetic field, n(r) and its derivatives. To get a stable sinusoidal modulation of a simple antiferromagnetic order, the ordinary and higher-order exchange stiffness constants are expected to be negative and positive, respectively. New interaction energies between elastic strains and derivatives of n(r), besides the ordinary magneto-elastic energy, are introduced to explain the transition between transversal and longitudinal spin density waves and the anisotropies, relative to the directions of modulation and polarization, of the susceptibility and dilatation and the anisotropy of orbital susceptibility is discussed; the nature of the transition at the Néel temperature is also discussed. The temperature variations of the maximum moment of SDW, specific heat and susceptibility are calculated and are compared with the experimental results for chrominum.