Anisotropy and quenched orbital moment in Sm-Co magnets

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Crystal structure of hexagonal SmCo5
Crystal structure of hexagonal SmCo5. Sm-1a, Co-2c, and Co-3g are three non-equivalent sites.

This CMI-funded research was conducted at Ames Laboratory.

Using electronic structure modeling, strong quenching  of orbital magnetic moment was identified as the prime cause of unusually high magnetic anisotropy in SmCo5

Significance and Impact:

  • Demonstrated validated theory and modeling techniques to resolve unsolved key permanent magnet parameters, such as magnetic anisotropy and orbital moment emerging from rare-earths
  • Sm-Co magnets offer relatively high energy-product at high-temperature suitable for technological applications from electric vehicles to wind turbines
set of four diagrams representing crystal field
(a) and (b) charge distribution and rare-earth moment in the easy and hard directions, (c) and (d) effect of crystal field on the charge distribution for the easy and hard directions

Details and Next Steps:

  • Electronic structure of the Sm atoms violates Hund's rules and the orbital moment is strongly quenched providing strong anisotropy and net 4f moment
  • Rationalizing the orbital-moment quenching in terms of the dependence of the 4f charge distribution, a long-run future research will be necessary to reconcile experiment, sub-lattice model, and ab-initio theory


B. Das, R. Choudhary, R. Skomski, B. Balasubramanian, A. K. Pathak, D. Paudyal, and D. J. Sellmyer, “Anisotropy and Orbital Moment in  Sm-Co Permanent Magnets,” Phys. Rev. B, 100, 024419 (2019).

diagrams of charge density calculated by using density functional theory
The charge density calculated by using density functional theory: (a) easy direction and (b) hard direction. The charge density has ranged from 
0 to 1 e/Å3.