Publications in Scientific Journals:
L. Udvardi, L. Szunyogh, K. Palotás, P. Weinberger:
"First-principles relativistic study of spin waves in thin magnetic films";
Physical Review B,
In order to study spin-wave excitations of itinerant ferromagnets a relativistic first-principles method based
on the adiabatic approach is presented. The derivatives of the free energy up to second order with respect of the
polar and azimuthal angles are derived within the framework of the magnetic force theorem and the fully
relativistic Korringa-Kohn-Rostoker method. Exchange and spin-orbit coupling are thus incorporated on equal
footing in the Hamiltonian. Furthermore, a detailed comparison to classical spin Hamiltonians is given and it
is shown that the magnetocrystalline anisotropy energy contains contributions from both the on-site anisotropy
and the off-site exchange coupling terms. The method is applied to an Fe monolayer on Cu~001! and Au~001!
surfaces and for a Co monolayer on Cu~001!. The calculations provide with the gap at zero wave number due
to the spin-orbit coupling and uniaxial anisotropy energies in good agreement with the results of the band
energy difference method. It is pointed out that the terms in the spin-wave Hamiltonian related to the mixed
partial derivatives of the free energy, absent within a nonrelativistic description, introduce an asymmetry in the
magnon spectrum with respect to two in-plane easy axes. Moreover, in the case of an in-plane magnetized
system the long-wavelength magnons are elliptically polarized due to the difference of the second-order
uniaxial and fourth-order in-plane magnetic anisotropy.
DOI: 10.1103/PhysRevB.68.104436 PACS number~s!: 75.10.Jm, 75.30.Ds, 75.30.Gw, 75.70.Ak
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