238 INTERMAG 2006

238 INTERMAG 2006238 INTERMAG 2006

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The (Zr0.67Sm0.33)(CoCuFe)3 phase in Sm(CoFeCuZr)z magnets.

F. P. Missell1,4, M. F. De Campos1, S. A. Romero2, R. K. Murakami1,2, A. C. Neiva3 andH. R. Rechenberg2

1. DIMCI/DIMAT, INMETRO - Instituto Nacional de Metrologia, Normalizacao e QualidadeIndustrial, Duque de Caxias, RJ, Brazil; 2. Instituto de Fisica, Universidade de Sao Paulo, SaoPaulo, SP, Brazil; 3. Engenharia Quimica - Escola Politecanica, Universidade de Sao Paulo, SaoPaulo, SP, Brazil; 4. Centro de Ciencias Exatas e Tecnologia, Universidade de Caxias do Sul,Caxias do Sul, RS, Brazil

The achievement of high coercivity in 2:17 magnets depends upon the presence of Zr, althoughthere is some disagreement as to its role. The important role of Zr in stabilizing the high tempera-ture 1:7 phase has been emphasized. In the final magnets, the Zr appears mainly in a Zr-richplatelet phase (14-18 at.% Zr), coherent with the cell and boundary phases and formed duringisothermal aging. Rabenberg et al. [1] proposed that the platelet phase has a rhombohedral SmCo3structure, but this was challenged by others who proposed a hexagonal Th2Ni17 structure for thisphase. It has been proposed that the function of the Zr might be to improve the imperfect shape ofthe cell walls and thereby increase coercivity.We have investigated samples of composition Sm(CobalFe0.2Cu0.1Zrx)8 (x = 0; 0.02; 0.04; 0.06,0.08) which were prepared by arc-melting the elements. Samples were homogenized for 4h at1175°C and then quenched into water. An isothermal heat treatment for 7h at 820°C was followedby a slow cooling (-1°C/min) to 400°C. After an isothermal treatment for 3h at this temperature, thesamples were cooled in air. The microstructure of samples with higher Zr content (x = 0.04, 0.06,0.08) is complex [2] and three phases were found with very different stoichiometries from the phas-es usually encountered (1:5, 1:7, 2:17). This work deals with a quinary phase which was observedin samples with x = 0.04 and 0.08 [2]. Our previous EDX measurements revealed the quinary phaseto have a composition around Zr 12, Sm 8.5, Co 60, Fe 15.5, Cu 4 at%. A phase with a very simi-lar composition had been observed previously by Bailey and Harris [3] in an as-cast, coredSm(Co0.66Fe0.21Cu0.10Zr0.03)7.37 alloy. The composition of the phase mentioned by thoseauthors is Sm(Co0.65Fe0.16Cu0.05Zr0.14)10.36. Zhang et al. [4] reported a phase with nearlyidentical composition in an alloy Sm(Co69Fe25.1Cu5.4Zr0.56)8.5 which was cast and then agedfor 40 h at 800°C. Zhang et al. arrived at this composition from an examination of a coarsenedplatelet phase using an electron probe microanalyzer (EPMA) and they identified this phase as theplatelet phase. The structure of the phase was investigated by selected area diffraction and wasfound to be consistent with a hexagonal cell of dimensions a ~ 0.5 nm and c ~ 0.8 nm.Samples with the composition of our quinary phase were prepared by arc melting and then homog-enized at 1050°C. EDX measurements revealed a phase with composition around(Zr0.67Sm0.33)(CoFeCu)3. A Rietveld refinement of an x-ray diffraction spectrum was performedusing Topas software. This analysis revealed that the sample consisted mainly (~70%) of a rhomb-hohedral 1:3 phase with lattice parameters a = 0.5 nm and c = 2.4 nm. These values are in goodagreement with those of Xiong et al. [5] who have proposed that the platelet phase is rhombohe-dral with the Be3Nb or PuNi3 structure. Initial room temperature magnetic characterization of ahomogenized ternary sample of (Zr0.67Sm0.33)Co3 is shown in the figure below.

[1] L. Rabenberg, R. K. Mishra, G. Thomas, IEEE Trans. Magn. MAG-19 (1983) 2723.[2] M. F. de Campos, A. C. Neiva. S. A. Romero, H. R. Rechenberg, F. P. Missell, J. Alloys Comp.403 (2005) 329-334.[3] T. Bailey and I. R. Harris, Proc. 9PthP International Workshop on Rare Earth Magnets and TheirApplications, Bad Soden, 1987, pp. 153-156.[4] B. Zhang, J. R. Blachere, W. A. Soffa, and A. E. Ray, J. Appl. Phys. 64 (1988) 5729.[5] X. Y. Xiong, T. Ohkubo, T. Koyama, K. Ohashi. Y. Tawara, K. Hono, Acta Mater. 52 (2004) 737.

Figure 1 - Specific magnetization vs. exter-nal magnetic field for homogenized(Zr0.67Sm0.33)Co3 measured at room tem-perature