Nonlocal torque operators in ab initio theory of the Gilbert damping in random ferromagnetic alloys

Abstract

We present an ab initio theory of the Gilbert damping in substitutionally disordered ferromagnetic alloys. The theory rests on introduced nonlocal torques which replace traditional local torque operators in the well-known torque-correlation formula and which can be formulated within the atomic-sphere approximation. The formalism is sketched in a simple tight-binding model and worked out in detail in the relativistic tight-binding linear muffin-tin orbital (TB-LMTO) method and the coherent potential approximation (CPA). The resulting nonlocal torques are represented by nonrandom, non-site-diagonal and spin-independent matrices, which simplifies the configuration averaging. The CPA-vertex corrections play a crucial role for the internal consistency of the theory and for its exact equivalence to other first-principles approaches based on the random local torques. This equivalence is also illustrated by the calculated Gilbert damping parameters for binary NiFe and FeCo random alloys, for pure iron with a model atomic-level disorder, and for stoichiometric FePt alloys with a varying degree of L10 atomic long-range order.

16 pages, 5 figures (several minor changes, accepted in the Physical Review B)

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• The relation of the Dzyaloshinskii-Moriya interaction to spin currents and to the spin-orbit field
• Mechanisms behind large Gilbert damping anisotropies
• Comparative study of methodologies to compute the intrinsic Gilbert damping: interrelations, validity and physical consequences
• Intrinsic Damping Phenomena from Quantum to Classical Magnets:An ab-initio Study of Gilbert Damping in Pt/Co Bilayer
• Influence of non-local damping on magnon properties of ferromagnets
• Gilbert damping in non-collinear magnetic system
• Ab initio theory of the spin-dependent conductivity tensor and the spin Hall effect in random alloys
• Electron transport in high-entropy alloys: Al${}_x$CrFeCoNi as a case study
• Dynamics of spin relaxation in nonequilibrium magnetic nanojunctions
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• Static transport properties of random alloys: vertex corrections in conserving approximations