Ab initio calculation of electronic structure and magnetic properties of R2Fe14BNx (R = Pr,Nd)

Guang Tian,Changsheng Wang,Liang Zha,Yingchang Yang,Guanyi Qiao,Jinbo Yang,Wenyun Yang

doi:10.1063/1.5007022

Guang Tian, Changsheng Wang + Show 5 more

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https://doi.org/10.1063/1.5007022

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Abstract

The site preference of N atom for R2Fe14BNx (R= Pr, Nd) and the interstitial nitrogen effect on the magnetic properties have been studied by the first-principles method. It was found that the nitrogen is more likely to occupy the 4e site for Pr2Fe14BNx compound, while 4f site for Nd2Fe14BNx. When N atoms entering some specific crystal sites (such as 2a and 4f), the total magnetic moments of these compounds are not reduced, but slightly increased. Although the doping of N may reduce the total magnetic moments of some R2Fe14B compounds in the cases of optimal occupancy, the volumetric effect caused by N doping can still change the electron density distributions of Fe near the Fermi level, improving the magnetic ordering temperature of such compounds.

Highlights

With the highest maximum energy product for the single phase compound, Nd2Fe14B based sintered magnets have been investigated extensively and used widely since being discovered in 1984.1,2 with the weaknesses common to rare earth-Fe compounds, R2Fe14B has a relatively low Curie temperature, which is disadvantageous for practical applications
On account of the small X-ray form factor and the complexity of neutron diffraction spectrum of R2Fe14BNx, it is difficult to determine the accurate occupancy of N atom from X-ray diffraction (XRD) or neutron diffraction study
The nitrides retain the structure of the parent compounds R2Fe14B, and the introduction of nitrogen into various crystal sites leads to different changes of the cell volume and magnetic properties

Summary

Introduction

With the highest maximum energy product for the single phase compound, Nd2Fe14B based sintered magnets have been investigated extensively and used widely since being discovered in 1984.1,2 with the weaknesses common to rare earth-Fe compounds, R2Fe14B has a relatively low Curie temperature, which is disadvantageous for practical applications. It was discovered that the magnetic properties of Sm2Fe17 and R(Fe,M)[12] can be improved substantially by introducing interstitial nitrogen.[3,4] Yang et al have first reported that nitrogen can be introduced into R2Fe14B structure by proper heat treatment and studied the magnetic properties of the nitrides.[5] A few earlier investigations about R2Fe14BNx focused mainly on the synthesis, structure chemistry and basic magnetic properties have been reported.[6,7,8] Among the nitrides of R2Fe14B compounds, it is learned that the addition of the nitrogen atoms raised Curie temperature as expected, but gave a negative effect on intrinsic magnetic properties, i.e. both saturation magnetization and magneto-crystalline anisotropy decrease.[6,7,8]. These information may provide guidance for the new materials development

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