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

I. Turek, J. Kudrnovský, and V. Drchal
Phys. Rev. B 92, 214407 – Published 3 December 2015
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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 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.

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  • Received 15 October 2015

DOI:https://doi.org/10.1103/PhysRevB.92.214407

©2015 American Physical Society

Authors & Affiliations

I. Turek*

  • Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, CZ-616 62 Brno, Czech Republic

J. Kudrnovský and V. Drchal

  • Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic

  • *turek@ipm.cz
  • kudrnov@fzu.cz
  • drchal@fzu.cz

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Issue

Vol. 92, Iss. 21 — 1 December 2015

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