Magnetic properties, phase evolution, and structure of melt spun SmCo7−xNbx (x=0–0.6) ribbons

Abstract

The phase evolution, microstructure, and magnetic properties of melt spun SmCo7−xNbx (x=0–0.6) ribbons have been investigated using powder x-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer, respectively. SmCo7−xNbx ribbons could crystallize in TbCu7-type structure only for low Nb substitution of x=0–0.3 at high wheel speed of 30–40 m/s. According to the structure refinement, the doping element Nb prefers to occupy the 2e site. The intrinsic coercivity increases dramatically from 1.9 kOe for SmCo7 ribbon to 10.2 kOe for SmCo6.8Nb0.2 ribbon at wheel speed of 40 m/s. The mechanism of the coercivity enhancement has been discussed. The optimal magnetic properties of σr=54.4 emu/g and Hic=10.2 kOe were obtained in SmCo6.8Nb0.2 ribbon.

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

“…3, where H c increases significantly from 1.7 kOe for undoped SmCo 7 to 11.5 kOe for SmCo 6.7 Nb 0.3 . Previous work [20] has reported similar change in H a with doping, however the origin of the increase in H a (or K) is still an open question, and we build upon this work by testing more realistic structure models and incorporating different doping levels to compare with experiment to validate the model results. Based on the mapping between simulation and experiment, we can attribute the origin of the dramatic changes in magnetocrystalline anisotropy with confidence.…”

“…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.…”

“…To address this challenge, previous models were based on the enthalpies of solution of the dopant ion M in liquid Sm and Co, i.e. using the atomic radius ratios of Sm to (Co, M), combined with the electronegativity differences between M, Sm and Co [13,20,21]. From this an estimate where M would locate itself in the lattice was possible.…”

“…The simulations indicated the origin of the significant increase in coercivity, H c (compared to pure SmCo 7 ) by incorporating the effects of Nb-doping, calculating the resultant H a , and bringing together the effects of grain size and H a . This work has been different from previous work [20] that the composition has been modified for comparing different Sm-Co systems. Detailed analyses based on first-principles density functional theory will be addressed.…”

“…Alloy ingots with a nominal composition SmCo 7Àx Nb x (0 6 Â 6 0.5) were prepared by arc melting [20,27,28]. The ingots were melted four times to ensure homogeneity, and then melt spun in an Ar atmosphere with a copper wheel at a speed of 40 m/s using a single-roller melt spinner.…”