Adiabatic spin dynamics from spin-density-functional theory: Application to Fe, Co, and Ni

Abstract

The adiabatic theory of spin-density waves is developed on the basis of spin-density-functional theory. The wave-number-dependent exchange constant matrix is obtained from spin-density-functional calculations with constrained moment directions. The central assumption considers a fast electronic and a slow magnetic time scale, and postulates negligible correlation of the fast motion between different ionic sites. The parameter-free calculated magnon spectra for Fe, Co, and Ni are in excellent agreement with available experimental data. In the case of Fe, they show strong Kohn anomalies. Using Planck statistics at low temperature, the temperature dependence of the magnetization is well described up to half the Curie temperature. It is conjectured that correlated local-moment clusters survive the Curie transition. On this basis, calculated Curie temperatures are obtained within 10% deviation from experiment for Fe and Co, but 30% to low for Ni. ͓S0163-1829͑98͒04425-7͔

Anab initioeffective Hamiltonian for magnetism including longitudinal spin fluctuations

“…In structure inverse methods one extracts the parameters for the Heisenberg model from the total energies of a set of magnetic structures. The structures used in this set are most often spin spirals, and there has been some debate as to whether small θ spin spiral or planar spin spiral structures should be used 2,3 . The alternative perturbative approach comes from considering the rotation of a pair of spins in some reference state by opposite and vanishing angles.…”

Competition of lattice and spin excitations in the temperature dependence of spin-wave properties

“…A review of the problem of adiabaticity in itinerant ferromagnets can be found in Ref. [52]. We have assumed here that the fundamental postulate of their theory holds, i.e., a much faster timescale of the electronic degrees of freedom with respect to the slow magnetic system, and further postulate that correlations of the fast ionic motion are negligible.…”

Electronic Structure and Magnetic Properties of Solids

“…Halilov at. al 36,37 have studied adiabatic spin waves computed using a frozen magnon method. This is analogous to the frozen phonon method where atoms are displaced from their equilibrium positions and the total energy is restored as a function of these positions.…”