Crystal structure and magnetic properties of melt spun SmCo7−xMx (M=Ta, Cr, and Mo; x=–0.6) ribbons

Abstract

The crystal structure and magnetic properties of melt spun SmCo 7−x M x ͑M = Ta, Cr, and Mo; x =0-0.6͒ ribbons have been investigated. Based on x-ray diffraction analysis, it is found that a pure TbCu 7 -type structure is formed in the melt spun SmCo 7−x Ta x ͑x=0-0.3͒ ribbons, while minor amount of additional 2:17 phase appears for the SmCo 7−x M x ͑M = Cr and Mo; x = 0.1-0.6͒ ribbons, implying that the elements in VI B group ͑Cr and Mo͒ are inferior to the element in V B group ͑Ta͒ in stabilizing metastable 1:7 phase. The result, analyzed by Rietveld refinement method, shows that Ta, Cr, and Mo may occupy the 2e site of 1:7 phase, which leads to the enhancement of the magnetic anisotropy field of 1:7 phase, just like Ti, Zr, Hf, Nb, or V did. From the magnetic performance point of view, with increasing the content of doping element x from 0 to 0.6, the maximum coercivity of SmCo 7−x M x ribbons is enhanced from 1.9 kOe for binary SmCo 7 to 11.3 kOe for M = Ta, 6.6 kOe for M = Cr, and 7.5 kOe for M = Mo, respectively, while the remanent magnetization is all reduced for the above ternary alloy ribbons.In order to search for novel permanent magnetic materials for high temperature applications, researches have been focused intensively on Sm͑Co, M͒ 7 alloys with TbCu 7 -type structure due to their excellent intrinsic magnetic properties. 1-13 The TbCu 7 -type structure can be regarded as a derivative of CaCu 5 -type structure ͑space group P6/mmm͒ in which a part of Sm atoms is disorderedly substituted by "dumbbell" pair of Co-Co, 1 and it keeps merit of the 1:5 structure, such as high anisotropy, and of the 2:17 structure, such as high magnetization and high Curie temperature. However, 1:7 is a metastable structure which is easy to decompose into 1:5 and 2:17 phases, and therefore, a third element is necessary to stabilize the SmCo 7 phase with TbCu 7 -type structure. Sm͑Co, M͒ 7 ͑M = Ti, Zr, Hf, Cu, Ga, Si, and Ag͒ magnets with a pure 1:7 phase, prepared by arc melting followed by lengthy annealing, have been reported to exhibit large magnetic anisotropy field, which resulted from the occupancy of M on the 2e or 3g sites of 1:7 crystal structure. [6][7][8]11,13 Furthermore, nanocrystalline Sm͑Co, M͒ 7 ͑M = Ti, Hf, Zr, V, and Nb͒ magnets prepared by arc melting followed by rapid solidification were shown to exhibit excellent coercivity. 9,10,14-16 Substitution of IV B group metals, i.e., Ti, Hf, Zr, and V B group metals, i.e., V or Nb, for Co in SmCo 7−x M x ͑M = Hf, Zr, V, and Nb; x = 0.1-0.3͒ ribbons, has been found to occupy 2e site of the TbCu 7 -type structure, and consequently, enhances the magnetic properties effectively. However, Ta is at the same V B group as that of V and Nb in periodic table, while Cr and Mo are located at the VI B group. It is of interest to realize whether those three elements play the same role as V and Nb in TbCu 7 structure or not.The alloys with the nominal composition of SmCo 7−x M x ͑M=Ta, Cr, and Mo; x=0-0.6͒ were prepared using arc melting in a high purity argon atmosphere. To c...

Effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7–xGex ribbons

“…According to Ref. In comparison with the results of previous studies, [8][9][10][11][12][13] the effect of the coercivity enhancement and the grain refinement along with the Ge substitution in the present study seems to be slightly lower than that with the refractory element's substitution. A negative enthalpy of solution of Ge in Sm is lower than that in Co, indicating that Ge might prefer to combine with more Sm.…”

Origins of the significant improvement in nanocrystalline Samarium–Cobalt’s magnetic properties when doping with Niobium

“…3. This increase in Hc is, the larger observed in the SmCo 6.7 M 0.3 system, which are limited by doping levels (x) is larger than 0.3, different phases appear [7,8,26,49], limiting the useful doping levels. Consider the magnetization versus field loops (half M-H loops) shown in Fig.…”

“…According to their calculations, Al, Nb, Ta, V and Ge would not stabilize the structure. However, Hsieh et al [16,17,26,27] and Guo et al [20,28] have successfully synthesized melt-spun compounds with M = Al, Nb, Ta, V, and Ge. Clearly, achieving correct simulation results is problematic.…”

Selecting Doping Elements by Data Mining for Advanced Magnets

“…In this respect, we spent over 10 years building up a specific database for Sm-Co systems, which contains both experimental and computational data for ∼1050 alloys published in the literature for decades, and some of them are used as references in this work. − ,,,− More importantly, we embedded in the database the related information search regarding composition, processing, microstructure, properties, and references of the material, which is unique from other material databases. The above specialized database may be considered as a “Materials Genome Initiative (MGI) , database of Sm-Co materials” according to its characteristics.…”