Interacting Stoner–Wohlfarth behavior in hysteresis curves of Sm(CoFeCuZr)z magnets

Several magnets with different Zr contents were studied: Sm(CobalFe0.2Cu0.1Zrx)8 (bal=balance; x=0, 0.02, 0.04, 0.06 and 0.08). The microstructure of the magnets includes three main phases, all crystallographically coherent: the cell phase Sm2(Co,Fe)17, the cell boundary phase Sm(Co,Cu)5 and a lamellar Zr-rich phase, rhombohedral (ZrSm)1Co3. The hysteresis curves were compared with the Callen, Liu and Cullen (CLC) modification of the Stoner–Wohlfarth model for an isotropic distribution of interacting single-domain particles. Choosing reasonable values for the saturation magnetization Ms, the anisotropy field Ha, and the mean-field interactions of the CLC model, we were able to reproduce the main features of the hysteresis curves for the x=0.02 and 0.04 samples. For higher x values, X-ray diffraction Rietveld analysis revealed the presence of other “impurity” phases, among them cubic Zr6(Co,Fe)23, rhombohedral (SmZr)5(CoFeCu)19 and rhombohedral (SmZr)2(CoFeCu)7.