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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Thermodynamics and Magnetism of SmFe12 Compound Doped with Co and Ni: An Ab Initio Study

Ni-doped Sm(Fe1−xCox)12 alloys are investigated for their magnetic properties. The Sm(Fe,Co)11M1 compound (M acts as a stabilizer) with the smallest (7.7 at.%) rare-earth-metal content has been recognized as a possible contender for highly efficient permanent magnets thanks to its significant anisotropy field and Curie temperature. The early transition metals (Ti-Mn) as well as Al, Si, and Ga stabilize the SmFe12 compound but significantly decrease its saturation magnetization. To keep the saturation magnetization in the range of 1.4–1.6 T, we suggest replacing a certain amount of Fe and Co in the Sm(Fe1−xCox)12 alloys with Ni. Ni plays the role of a thermodynamic stabilizer, and contrary to the above-listed elements, has the spin moment aligned parallel to the spin moment of the SmFe12 compound, thereby boosting its saturation magnetization without affecting the anisotropy field or Curie temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on SmFe12 by Materials Project

SmFe12 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sm is bonded to sixteen Fe atoms to form distorted face-sharing SmFe16 cuboctahedra. There are a spread of Sm–Fe bond distances ranging from 2.87–3.29 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a 6-coordinate geometry to two equivalent Sm and twelve Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.45–3.04 Å. In the second Fe site, Fe is bonded in a 12-coordinate geometry to one Sm and eleven Fe atoms. There are a spread of Fe–Fe bond distances ranging from 2.39–2.77 Å. In the third Fe site, Fe is bonded in a 7-coordinate geometry to one Sm and ten Fe atoms. Both Fe–Fe bond lengths are 2.26 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of Co on twin formation and magnetic properties of Sm(Fe,Ti,V) 12 alloys

Transferring the excellent intrinsic magnetic properties of SmFe 12 -based compounds to their extrinsic properties remains the main challenge in the development of high-performance SmFe12-based permanent magnets. Twin formation is one of the reasons for the inability to achieve high coercivity and remanence. Here we have shown that the addition of Co in Sm(Fe 1-x Co x ) 10–11 M 1–2 alloys, where M=Ti and V, leads to an increase in twin density. Microstructural characterizations revealed that the atomic arrangement in the twin boundary changes depending on the stabilizing element, which directly influences the local intrinsic magnetic properties. Theoretical investigations showed that the critical grain size at which twin formation can be hindered by grain size reduction decreases when the stabilizer changes from V to Ti. Furthermore, this study shows that the alloy composition influences not only the intrinsic magnetic properties but also the twin formation energy and its grain size dependence, crucial for the design of SmFe12-based permanent magnets.

36 MATERIALS SCIENCE↗