(Fe,Co)2(P,Si) rare-earth free permanent magnets: From macroscopic single crystals to submicron-sized particles

While rare-earth magnets exhibit unchallenged hard-magnetic properties, looking for alternatives based on inexpensive elements of non-critical supply remains of utmost interest. Here, we demonstrate that (Fe,Co)(2)(P,Si) single crystals combine a large magnetocrystalline anisotropy ( K-1 approximate to 0.9 MJ m(-3) at 300 K), high Curie temperatures (TC up to 560 K) and an appreciable saturation specific magnetization (101 A m(2) kg(-1)) leading to a theoretical |BH|(max) approximate to 165 kJ m(-3) , making them promising candidate materials as rare-earth-free permanent magnets. Our comparison between (Fe,Co)(2)P and (Fe,Co)(2)(P,Si) single crystals highlights that Si substitution reduces the low-temperature magnetocrystalline anisotropy, but strongly enhances T-C, making the latter quaternary alloys most favorable for room temperature applications. Submicron-sized particles of Fe1.75Co0.20P0.75Si0.25 were prepared by a top-down ball-milling approach. While the energy products of bonded particles are to this point modest, they demonstrate that perma-nent magnetic properties can be achieved in (Fe,Co)(2)(P,Si) quaternary alloys. This work correlates the de-velopment of permanent magnetic properties to a control of the microstructure. It paves the way toward the realization of permanent magnetic properties in (Fe,Co)(2)(P,Si) alloys made of economically competi-tive Fe, P and Si elements, making these materials desirable for applications. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study demonstrates that (Fe,Co)(2)(P,Si) single crystals have promising magnetic properties for potential use as alternatives to rare-earth magnets. Silicon substitution improves the Curie temperature of the material, making it suitable for room temperature applications.