Ab initio calculations of magnetic properties of the interstitially doped YFe 11 Mo compound
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LECTRONIC PROPERTIES OF SOLID
Ab Initio Calculations of Magnetic Properties of the Interstitially Doped YFe11Mo Compound1 E. E. Kokorina, M. V. Medvedev, and I. A. Nekrasov Institute of Electrophysics, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620016 Russia e-mail: [email protected]; [email protected] Received July 19, 2015
Abstract—The recent increase in the number of studies of RFe11 – xMx compounds is related to their promising application as permanent magnets. However, the insufficiently high value of the Curie temperature TC of these compounds is a barrier to their widespread use. The increase in the Curie temperature of these compounds is achieved by doping with the light nonmetallic atoms such as hydrogen, nitrogen, and carbon. In this paper, it is shown numerically that this doping leads to drastic changes of the electronic band dispersions in a wide energy region around the Fermi level. This in turn changes values of the magnetic moments of ions and Heisenberg exchange interaction parameters. The values of ab initio calculated magnetic moments and direct exchange interaction parameters make it possible to calculate the Curie temperatures for both parent and nitrogen-doped compounds within the mean-field approach to the Heisenberg model in the sample of YFe11Mo, a typical representative of the R(Fe,M)12L class. Theoretical values of TC obtained for YFe11Mo and YFe11MoN (514 and 723 K respectively) are consistent with experimental ones (472 and 664 K) with an accuracy of 10%. Also, the calculated increase in TC upon nitrogenization (about 200 K) is in good agreement with the experimental data. DOI: 10.1134/S1063776116020059
1. INTRODUCTION The discovery of relatively inexpensive intermetallic compounds Nd–Fe–B with high saturation magnetization has raised interest in the development of R–Fe–M systems (R = rare earth and M = Al, Ti, V, Cr, Mo, W, Si is a transition metal or metalloid) to use them as permanent magnets. Among these systems, R(Fe,M)12 compounds have attracted particular attention due to a relatively high Curie temperature (TC), noticeable saturation magnetization, and large uniaxial magnetocrystalline anisotropy at room temperature. It has been established that the structure stability element M plays a key role in the formation of R(Fe,M)12 structures that do not exist in the pure RFe12 form [1]. Investigations of R(Fe,M)12L systems (L = N, C, H is the interstitial atom) were mainly carried out under the expectation to enhance their technologically useful hard magnetic properties [2–4]. Also, a significant increase in the Curie temperature observed upon light-element doping is an important feature for technological applications. To our knowledge, however, some phenomena related to these compounds are yet to be explained. In particular, the elementary lattice increases in volume upon doping, which in its turn decreases the electronic shell overlapping and corresponding exchange interactions. The 1The article is published in the original.
latter may reduce the Curie temperat
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