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.

Achievement:
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

Publication:

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.