Abstract
In this report we present a systematic study of the magnonic modes in the disordered Fe0.5Co0.5 alloy based on the Heisenberg Hamiltonian using two complementary approaches. In order to account for substitutional disorder, on the one hand we directly average the transverse magnetic susceptibility in real space over different disorder configurations and on the other hand we use the coherent potential approximation (CPA). While the method of direct averaging is numerically exact, it is computationally expensive and limited by the maximal size of the supercell which can be simulated on a computer. On the contrary the CPA does not suffer from this drawback and yields a cheap numerical scheme. Therefore, we additionally compare the results of these two approaches and show that the CPA gives very good results for most of the magnetic properties considered in this report, including the magnon energies and the spatial shape of the eigenmodes. However, it turns out that while reproducing the general trend, the CPA systematically underestimates the disorder induced damping of the magnons. This provides evidence that the physics of impurity scattering in this system is governed by non-local effects missing in the CPA. Finally, we study the real space eigenmodes of the system, including their spatial shapes, and analyze their temperature dependence within the random phase approximation.
Highlights
Over the last few decades, the field of magnon spintronics, or magnonics, gained an ever increasing amount of attention
In this report we present a systematic study of the magnonic modes in the disordered Fe0.5Co0.5 alloy based on the Heisenberg Hamiltonian using two complementary approaches
Both iron and cobalt are known for long ranged interaction between the magnetic moments, the results presented use only 12 shells of neighbors because of computational limits
Summary
Over the last few decades, the field of magnon spintronics, or magnonics, gained an ever increasing amount of attention. The interaction of magnons with electronic excitations including a spin flip, called Stoner excitations, plays an essential role especially in metals [15,16,17] This mechanism, called Landau damping, was shown to be affected by reduced dimensionality of the system and alloying [18]. On the other hand we utilize a CPA applied to the disordered Heisenberg ferromagnet [19] This mean field approach was successfully applied for the calculation of electronic and magnetic properties in numerous materials, e.g. S Paischer et al not describe the reduction of the magnon life-time due to the interaction of these modes with the thermal bath mentioned above We show that both MC and CPA methods give the same magnetic spectrum and the spatial shape of the eigenmodes.
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