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Abstract: The base alloys of nominal composition (Nd0.75Pr0.25) y FebalanceB x (y=10−9.2 and x=6−19.2) were chosen to study the influence of RE/B ratio, smaller than stochiometric composition on magnetic properties of over quenched and annealed ribbons. From X-ray diffraction analysis of these ribbons, the α-Fe and Fe3B phases were observed along with (Nd,Pr)2Fe14B major phase. The average grain size was calculated using these patterns as: 35nm for α-Fe, 45nm for (Nd,Pr)2Fe14B and 22nm for Fe3B particles. TEM analysis also supported the nano distribution of the above phases. These X-ray graphs support the idea of exchange coupling between hard and soft phases responsible for the observed magnetic properties. In these ribbons the saturation magnetization J s and remnant magnetization J r increases from 1.19T to 1.66T and from 0.65T to 0.91T, respectively as RE/B ratio increases. The increase in J s and J r may be attributed to the presence of exchange coupling between these phases. The corresponding coercivity j H c decreases from 673.33 to 271.33kAm−1. The maximum energy product (BH)max initially increases from 72.42kJm−3to 109.85kJm−3 up to RE/B≈1 and then decreases to 58.5kJm−3, depending on the shape of second quadrant B–H loop. The coercivity mechanism observed from initial hysteresis curve was considered to be nucleation of domain wall. [Copyright &y& Elsevier]

The effects of Zr and C additions on the magnetic properties and microstructures of melt-spun Fe83-xZrxNd10B7-yCy (x=0–5, y=0–7) alloys were investigated. The cooling rates of melts were varied by changing the wheel surface velocity to optimize hard magnetic properties. The Zr addition decreased the size of the crystalline grains and increased the coercivity from 6.6 kOe for Fe83Nd10B6C1 to 10.7 kOe for Fe78Zr5Nd10B6C1. The C addition compensates the decrease of remanence caused by the addition of Zr. The (BH)max of 145 kJ/m3 was obtained from an optimally cooled Fe80Zr3Nd10B6C1 alloy. [Copyright &y& Elsevier]

The effect of minor elements (Cu, Nb, Zr and/or Ga) on the microstructure and magnetic properties of α-Fe/Nd2Fe14B nanocomposites obtained by melt-spinning Nd8Fe87B5 based alloys has been studied by using three-dimensional atom probe and transmission electron microscopy. Cu atoms form clusters prior to the crystallization of amorphous precursors. However, Cu clusters do not act as heterogeneous nucleation sites for the α-Fe crystals; thus, Cu addition is not beneficial for reducing the grain size of α-Fe/Nd2Fe14B nanocomposites. On the other hand, Nb is effective in suppressing grain growth while annealing an partially crystallized melt-spun Nb-containing alloy. However, it was not possible to optimize the microstructures and magnetic properties by crystallizing Nb-containing amorphous precursors. The hard magnetic properties with Hc=496 kA/m and (BH)max=134 kJ/m3 were obtained by adding a small amount of Zr. The coercivity was enhanced by combined addition of Zr and Ga. Zr and Ga atoms are partitioned into the Nd2Fe14B phase, and evidence for a slight enrichment of Zr atoms at the α-Fe/Nd2Fe14B interfaces has been found. [Copyright &y& Elsevier]

Abstract: SmCo3Cu2/α-Fe nanocomposites have been obtained by mechanical milling (MM) of a SmCo3Cu2+30wt% α-Fe mixture and subsequent annealing. The progressive structural modifications were checked by X-ray diffraction (XRD). The width of the diffraction peaks of the hard magnetic phase was found to increase with milling time and the peaks almost disappeared after 9h of milling. The characteristic diffractions peaks of the SmCo5-type phase could be restored by applying an appropriate heat treatment. The magnetic behavior of the SmCo3Cu2/α-Fe nanocomposite was studied versus milling and annealing conditions. A dramatic decrease in both the coercivity and the remanence was observed after milling. Considering the importance of the microstructure for the coercivity development in the SmCo3Cu2 bulk alloys, the hard magnetic properties of the SmCo3Cu2/α-Fe nanocomposite are discussed in comparison with those characterizing bulk SmCo3Cu2. [Copyright &y& Elsevier]