Structure and magnetic properties of bulk nanocrystalline SmCo6.6Nb0.4 permanent magnets

Abstract

The crystal structure and magnetic properties were studied for the bulk nanostructural permanent magnet SmCo6.6Nb0.4 prepared by spark plasma sintering method. The magnet crystallizes in a single phase with a hexagonal TbCu7-type crystal structure after the sintering process. Rietveld fitting results show that the alloying element of Nb prefers to occupy the 3g site. Microstructure observation indicates that the average crystal grain size is about 30nm. The coercivity decreases almost linearly from 2.8to0.5T with increasing temperature from 300to773K. A remanence enhancement resulting from intergrain exchange coupling among the fine grains was also observed.

Effects of Hf and CNTs on magnetic transformation and thermal stabilities of TbCu7-type Sm–Co matrix ribbon magnets

“…large anisotropy field [1] and low intrinsic coercivity temperature coefficient [2,3]. SmCo 7 can have a TbCu 7 -type hexagonal crystal structure (for short 1:7H) with a space group of P6/mmm, and its composition lies between that of SmCo 5 (for short 1:5) and Sm 2 Co 17 (for short 2:17).…”

“…Si [12] and Ga [1]; the third is palladium group elements with non-full 4d-shell, e.g. Zr [10,11,13], Nb [2], Ag [12] and Mo [14] and platinum group elements with non-full 5d-shell, e.g. Hf [10,12,[15][16][17][18].…”

Structural and magnetic properties of SmCo5.6Ti0.4 alloy

“…If 1 3 ( 3 9 ) of the Sm sites of the 1:5 structure are substituted by Co-Co dumbbell pairs and the substitution is ordered, the 2:17 structure (Th 2 Zn 17 ) is formed. While reducing the substitution to 2 9 , the disordered SmCo 7 structure will be formed [6][7][8][9][10][11]. However, it is not clear on the structural and magnetic properties in the SmCoTi compounds, if the substitution is further reduced to less than 2 9 .…”

Bulk anisotropic nanocrystalline SmCo6.6Ti0.4 permanent magnets

“…The inset in Figure 1b is the selected area electron diffraction (SAED) pattern of a single milled flake. The polycrystalline diffraction rings are composed of several symmetrical discontinued segments (clearly seen in the diffraction ring of {2 0 0}), which shows that there is a texture in the as-milled powder sample because in three-dimensionally randomly oriented nanocrystalline samples the diffraction ring is continuous and homogeneous [14,16]. In addition, only the diffraction rings of the crystallographic planes parallel ({2 0 0}, {2 2 0} and {4 0 0}) or close ({2 1 1}) to the [0 0 1] direction in the TbCu 7 -type crystal structure are visible, indicating that the flake was out-of-plane [0 0 1] textured, which is in good agreement with the XRD results in Figure 1a.…”

“…), but the ascast alloys exhibit poor coercivity [11][12][13]. Nanocrystalline TbCu 7 -type SmCo permanent magnets possess large coercivity of more than 1600 kA m À1 due to strong pinning of the domain walls at the nanocrystalline grain boundaries [14]. However, their remanence is relatively low because the magnets are crystallographically isotropic.…”