Researchers have discovered a potential tool to enhance magnetization and magnetic anisotropy, making it possible to improve the performance of samarium-cobalt (Sm-Co) magnets. Sm-Co magnets were the first rare-earth permanent magnets, and are still the top performer in applications where resistance to demagnetization—its coercivity—and performance at high temperatures are important.
A paper on the work is published in the journal Physical Review B.
The scientists, at the US Department of Energy’s Critical Materials Institute at Ames Laboratory, in collaboration with the Nebraska Center for Materials and Nanoscience and the Department of Physics and Astronomy at the University of Nebraska, identified orbital-moment quenching as the possible tool, and rationalized the quenching in terms of the dependence of electrical charge distribution in samarium atoms.
The scientists at first sought to test the limits of substituting iron for some of the cobalt, attempting to make a Sm-Co magnet comparable in strength to neodymium iron boron (Nd-Fe-B) magnets, which has a higher magnetic moment.
The Critical Materials Institute (CMI) has as one of its moonshots the discovery of materials that are comparable in strength to neodymium magnets, but with the high-temperature durability of samarium magnets. We were looking to increase the magnetic moment of the standard Sm-Co magnet.—Durga Paudyal, Ames Laboratory scientist and project leader for Predicting Magnetic Anisotropy at CMI
The research collaboration led to the discovery that substitutions of iron could range as high as 20 percent, keeping the coercivity of the magnet intact. Computational theory and modeling results showed that the electronic structure of the Samarium in the material may violate Hund’s rule, which predicts how electrons occupy available orbitals in the atomic structure.
The research findings will help scientists sort out the parameters of magnetism in rare-earth materials, and help speed discovery of potentially useful magnets in the future.
The Critical Materials Institute is a Department of Energy Innovation Hub led by the US Department of Energy’s Ames Laboratory and supported by the Office of Energy Efficiency and Renewable Energy’s Advanced Manufacturing Office, which supports early-stage research to advance innovation in US manufacturing and promote American economic growth and energy security. CMI seeks ways to eliminate and reduce reliance on rare-earth metals and other materials critical to the success of clean energy technologies.
Bhaskar Das, Renu Choudhary, Ralph Skomski, Balamurugan Balasubramanian, Arjun K. Pathak, Durga Paudyal, and David J. Sellmyer (2019) “Anisotropy and Orbital Moment in Sm-Co Permanent Magnets,” Phys. Rev. B 100, 024419 doi: 10.1103/PhysRevB.100.024419