Correlation of hard magnetic properties and microchemistry of Sm-Co-Fe-Cu-Zr magnets with varying Fe concentration

Abstract

Wide application of high-temperature type permanent magnets (HTPM) in XXI century stimulated a renewed interest in the understanding of elemental redistribution between the constituent phases (SmCo5 (1:5) and Sm2Co17 (2:17) phases of the cellular structure) by means of high resolution transmission electron microscopy (TEM) with energy dispersive x-ray spectroscopy (EDS) [1] and for three-dimensional near atomic scale distribution using atom probe tomography (APT) [2,3]. However, details of the elemental redistribution are still a subject for discussion. A number of work has demonstrated that Cu concentration reaches maximum at the center of the 1:5 phase [1,2]. In the case of high-energy permanent magnets (HEPM) prepared from Fe-rich alloys, verification of this result is complicated by the limited fraction of the 1:5 phase and small size of precipitations. The goal of this work is to compare peculiarities of structural transformations in HTPM and HEPM in the course of slow cooling with temperature decreasing stepwise from 830 to 400°C. Two types of magnets with varying Fe concentration, i.e., Sm(Co0.88-xFexCu0.09Zr0.03)7 with x = 0 – 0.12 (the HTPMs) and Sm(Co0.91-xFexCu0.06Zr0.03)7.5 with x = 0.24 – 0.33 (the HEPMs) were studied at different temperatures of heat treatment for phase formation by x-ray diffraction followed by magnetic property measurements [4]. Microstructure characterization performed using TEM and APT of the HEPM Sm(Co0.63Fe0.28Cu0.06Zr0.03)7.6 sample after the complete thermal treatment demonstrated that it has a well-developed cellular nanostructure. Demagnetization curves measured at a temperature of 550°C close to the Curie temperature of the 1:5 phase have inflections which suggest the formation at the 1:5/2:17 interface of the interlayers breaking the exchange coupling between 1:5 and 2:17 phases. New results on the redistribution of Sm, Co, Fe, and Cu between different phases obtained using APT will be presented and their influence on the magnetic properties will be discussed. 1. A. Yan, O. Gutfleisch, A. Handstein, T. Gemming, and K.-H. Müller, J. Appl. Phys. 93, 7975 (2002). 2. R. Gopalan, K. Hono, A. Yan, and O. Gutfleisch, Scr. Mater. 60, 764 (2009). 3. H. Chen, Y. Wang, Y. Yao, J. Qu, F. Yun, Y. Li, S. P. Ringer, M. Yue, and R. Zheng, Acta Mater. 164, 196 (2019). 4. A. G. Popov, O. A. Golovnia, V. S. Gaviko, D. Y. Vasilenko, D. Y. Bratushev, V. I. N. Balaji, A. Kovács, K. G. Pradeep, and R. Gopalan, J. Alloys Compd. 820, 153103 (2020).