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A.V. Ruban, S. Khmelevskyi, P. Mohn, B. Johansson:
"Temperature-induced longitudinal spin fluctuations in Fe and Ni";
Physical Review B, 75 (2007), 0544021 - 0544027.

We have developed an ab initio framework for calculating parameters of a high-temperature magnetic
Hamiltonian. In the adiabatic approximation, this includes transverse and longitudinal magnetic excitation
spectra on equal footing. The exchange interaction parameters of the Hamiltonian for bcc Fe and fcc Ni are
determined from constrained local spin-density approximation calculations. Finite temperature magnetic properties
of the resulting model Hamiltonian are then investigated by a Monte Carlo simulation technique. The
calculated Curie temperatures and paramagnetic susceptibilities are in good agreement with experimental data
for both metals. We demonstrate that the temperature-induced longitudinal spin fluctuations are important for
high temperature properties such as susceptibility and magnetic specific heat.