Anisotropy and orbital moment in Sm-Co permanent magnets

Abstract

Structural and magnetic properties of iron-free and iron-substituted SmCo5 have been investigated theoretically and experimentally. The nanocrystalline ribbons of SmCo5−xFex(0≤x≤2), which were produced by rapid solidification, crystallize in the hexagonal CaCu5 structure for x≤0.75. Small Fe additions (x=0.25) substantially improve the coercivity, from 0.45 to 2.70 T, which we interpret as combined intrinsic and extrinsic effect. Most of our findings are consistent with past samarium-cobalt research, but some are at odds with findings that have seemingly been well established through decades of rare-earth transition-metal research. In particular, our local spin-density approximation with Hubbard parameter calculations indicate that the electronic structure of the Sm atoms violates Hund's rules and that the orbital moment is strongly quenched. Possible reasons for the apparent disagreement between theory and experiment are discussed. We explicitly determine the dependence of the Sm 4f charge distribution, arguing that an accurate densityfunctional description of SmCo5 is a challenge to future research.

Modelling of phase stability: integrating computational materials science and materials informatics

“…Based on first-principles calculations, as shown in Figure 8A, Das et al [100] found that the formation energy of SmCo 5 increased with increasing Fe doping content, while the magnetocrystalline anisotropy energy [49,99] .…”

“…Due to the complexity of the cell structure and the diversity of the doping sites, the computation period is usually long. For permanent magnetic materials, to obtain sufficient information of the cell structure of a certain phase in the doped system and the related electronic and magnetic structures, the all-electron method should be used to solve the wavefunction [100] , which is extraordinarily time-consuming. However, other methods of first-principles calculations generally have poor convergence when dealing with 4f electrons.…”

“…Figure 8. First-principles calculation results and analysis from Das et al[100] , Söderlind et al[101] , Gavrikov et al[102] . (A) Calculated magnetocrystalline anisotropy and formation energies of the SmCo 5-x Fe x phase as a function of Fe content.…”

Structural transformation and magnetic properties of (Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with 5$d$ elements: A combined first-principles and experimental study

“…Permanent magnets are one of the most important materials used in modern technology. The best known and widely used permanent magnets are characterized by high T C values, such as SmCo 5 alloys [1], and high energy product (BH) max , where the most obvious example is Nd 2 Fe 14 B [2]. As rare earth prices have shown high volatility over the past decade, the search for highenergy product magnets with limited content of elements such as Sm or Nd has intensified [3][4][5].…”

Effect of transition metal doping on magnetic hardness of CeFe$_{12}$-based compounds

“…They have remarkable magnetic properties, such as very high energy density (BH) max and the ability to operate at high temperatures. Of particular interest are rare-earth compounds such as Nd 2 Fe 14 B [1] and SmCo 5 [2] showing extremely high values of magnetocrystalline anisotropy. However, the high volatility of rare earth prices that became clearly evident during the so-called rare-earth crisis of 2011 [3] has mobilized the international research community to search for a new generation of hard magnetic materials with reduced rare-earth content [4][5][6][7][8][9][10].…”