Magnetic Properties of Nanostructured Rare Earth-Fe Compound Produced by HDDR Process

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Purpose : Remanence enhanced magnets made from a 2 phase nanostructure of hard and soft magnetic phases, can be prepared by either melt spinning or by mechanical alloying. Our previous work has shown that a 2 phase mixture can also be obtained by the Hydrogenation Disproportionation Desorption Recombination (HDDR) processing of Sm3(Fe,V)29 into TbCu7 type and αFe(V) phases, which exhibits coercivities of about 0.6 MAmィイD1-1ィエD1 (7kOe) after nitriding. However, the grain size of HDDR processed materials (〜300 nm) is typically an order of magnitude larger than that necessary for remanence enhancement to occur : the soft grains should ideally be 10 - 20 nm. The addition of Co has been shown to be effective in reducing the recombination temperature and grain size of HDDR treated samples. Therefore, the aim of this work was to investigate the effect of Co on the disproportionation and recombination kinetics of Sm3(Fe,V)29, and to attempt to reduce the grain size of the aFe(Co,V)/TbCu7 type … More phase mixture.Experimental Procedure : Alloys of Sm9.4Fe84.6-XCoXV6.0 (X=0, 10, 20 and 30), were induction melted from high purity elements, under an Ar atmosphere, and then homogenized at 1150℃ for 20 hours. X-ray diffraction (XRD) analysis showed that the alloys were near single phase Sm3(Fe,Co,V)29 with a small amount of aFe(Co,V). The homogenized alloys were ground into powders, sieved to a particle size less than 63μm, and pressed into green compacts. Samples were obtained at different stages of the disproportionation reaction, by heating under hydrogen to temperatures between 620 - 700℃, and then after 1 hour, cooling rapidly in hydrogen. HDDR samples were obtained by heating the disproportionated samples under vacuum to temperatures between 590 - 750℃, and then after 10 min - 12 hours, cooling rapidly under vacuum. Some of the HDDR samples were then nitrided at 560℃ for 4 hours 3), then ground into powder, which was mixed with molten paraffin that solidified within a magnetic field of 1.0 MAm-1(12 kOe). The magnetic properties were measured using a vibrating sample magnetometer (VSM). Samples for transmission electron microscopy (TEM) were thinned by ion milling.Results : with the addition of cobalt, the disproportionation temperature of the alloys Sm9.4Fe84.6-XCoXV6.0 (X=0, 10, 20, 30) increased, and the recombination temperature decreased. This shows that cobalt stabilizes the Sm3(Fe,Co,V)29 phase with respect to disproportionation in hydrogen, and increases the rate of the recombination into aFe(Co,V) and TbCu7 type phases. With TEM 【approximately equal】5 nm diameter rods were observed, which are believed to be SmH2. Grains about 50-100 nm in size were found in a 30% Co sample recombined at 630℃ for 1 hour. In addition to aFe(Co,V) and TbCu7 type phases, XRD also showed the presence of a yet unidentified phase that forms at high Co contents and low temperatures, which appeared to have an adverse effect on the magnetic properties, after nitriding. Less