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Quaternary alloys based on Ni[sub50]Mn[sub30]Ga[sub20] (an off-stoichiometric Heusler alloy, Ni[sub2]MnGa), with an intended substitution of 10 at. pet Ni by Fe or Co and with a 5 at. pet substitution of Ga by Al, were prepared by vacuum arc melting and heat treated. The as-cast and heat-treated alloys were characterized for their structural, thermal, and magnetic properties. The saturation magnetization improved with the addition of ferromagnetic elements Fe or Co and decreased with the Al addition. All three of the substitutions lowered the martensite transformation temperature, due to a reduction in the electron-to-atom (e/a) ratio for the Fe/Co additions or due to the more open structure resulting from the lower atomic size, in the ease of the Al substitutions. Martensite transformation studied through thermal and thermomagnetic analysis methods shows a single-stage transformation in the case of the Fe/Co substitutions, whereas the Al substitution resulted in a two-stage transformation. [ABSTRACT FROM AUTHOR]

Structural transformations and microstructural characterisation of Sm2Co17 alloys containing Fe, Cu and Zr at different stages of thermal processing have been investigated by X-ray diffraction, optical, scanning electron and transmission electron microscopes. Solution treated samples consist of a mixture of hexagonal TbCu7 (1:7 H) and rhombohedral Th2Zn17 (2:17 R) structure types of 2:17 phase. After isothermal aging, TbCu7 + Th2Zn17 structures transform into Th2Zn17 type structure with precipitation of Cu-rich hexagonal SmCo5 (1:5 H) and Zr-rich platelet phases. In addition to the main phases, a soft magnetic phase of composition Zr6(FeCo)23 is formed in alloys containing higher Zr composition. Isothermal aging studies reveal that magnetic properties show a peak value when aged at 1108–1123 K for 10 h. TEM studies show cellular precipitate structure with cell interiors having 2:17 R structure, while the fully coherent cell boundaries have the 1:5 H structure. Zr-rich platelets which run across many cells and cell boundaries were found to have 1:7 H structure. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the magnetic and microstructural properties of neodymium[sub 16.8]iron[sub 75.7-x]aluminum[sub x]boron[sub 7.5]. Methodology; Results and discussion; Conclusions.

Abstract: Structural transformation, microstructure and magnetocaloric effect (MCE) were investigated in melt-spun Ni55Mn20.6Ga24.4 and Ni55Mn19.6Ga25.4 ribbons. Magnetic and thermal studies of the ribbons revealed the occurrence of simultaneous structural and magnetic transitions near room temperature with a narrow thermal hysteresis of magnetization ≈2K. Maximum entropy changes (ΔS M) of −9.5 and −10.4J/kgK have been obtained at 309K for a field change of 2T in Ni55Mn20.6Ga24.4 and Ni55Mn19.6Ga25.4 ribbons, respectively. The Ni55Mn19.6Ga25.4 ribbon exhibits refrigeration capacity (RC) of 47J/kg with low average hysteresis loss (≈1.5J/kg) at the merged structural and magnetic transition temperature. [Copyright &y& Elsevier]

Abstract: Highly dense SmCo5/Fe nanocomposite bulk magnets were prepared by spark plasma sintering of magnetic field-milled SmCo5/Fe nanocrsytalline powders. The sintering experiments were conducted with varying temperatures of 973–1123 K. The resultant bulk materials had densities of 85–98% and mean grain sizes of 17–30 nm. The SEM analysis showed that the bulk samples prepared at higher sintering temperature exhibited dense and uniform microstructure. The XRD studies in complement with energy dispersive x-ray analysis revealed that the bulk magnets sintered at or above 1073 K exhibited Sm(Co,Fe)5 as main phase, along with other secondary phases such as Sm2(Co,Fe)17 and α-Fe(Co). A single-phase behavior with high remanence ratios (0.67–0.77) for the nanocomposite magnets was demonstrated by the magnetic measurements. In the present study, the sintering temperature of 1073 K was found to be optimum in achieving relatively high coercivity (8.2 kOe), magnetization (97.5 emu/g) and energy product (69.6 kJ/m3) for the SmCo5/Fe nanocomposite bulk magnets. [Copyright &y& Elsevier]

Abstract: Fe–0.4wt% P alloy was processed by melting, forging, hot rolling with a subsequent two-step heat treatment and its magnetic properties were compared with those of non-oriented Si-steel. The sample heat treated at 1000°C for 1h followed by 500°C for 30min air quenched yielded a saturation magnetization (B s ) of 19kG and a low coercivity (H c ) of 1Oe. The soft magnetic properties obtained were correlated to the microstructure which showed nano precipitates of Fe3P in Fe matrix obtained by the two-step heat treatment procedure. [Copyright &y& Elsevier]

Abstract: Self-assembled Sm–Co nanoparticles in the form of spherical aggregates (referred as nanospheres) with diameter ranging from 50 to 180nm were achieved by means of polyol technique. The size distribution of the Sm–Co nanospheres can be regulated close to ∼100nm by controlling the molar ratio of Sm:Co precursor. The spherical aggregates exhibited Sm2Co7 phase as a major constituent; while the aggregates obtained at higher Co concentration showed co-existence of Co-phase with Sm2Co7 phase. Upon annealing, the biphasic nature of nanospheres (Sm2Co7/Co) transformed into Sm2Co17 structure. By varying the Sm:Co precursor ratio from 1:5 to 1:9, the coercivity (H c ) and magnetization (M s ) values of the as-synthesized nanospheres can be tuned from 336 to 140Oe and from 63.7 to 108emu/g, respectively, and these values significantly improved after annealing. Maximum values of H c (1050Oe) at the Sm:Co molar ratio of 1:5 and M s of 184.6emu/g at the Sm:Co molar ratio of 1:9 were achieved in the annealed samples. [Copyright &y& Elsevier]

Abstract: Melt-spun ribbons of Co69Fe7Si14B10 alloy have been prepared at different wheel speeds viz. 47, 34 and 17m/s and investigated for structural and magnetic properties. Degree of amorphicity in the as-spun ribbons is found to increase with wheel speed. Amorphous phase crystallizes in two stages producing Co2Si, Co2B and CoSi phases on annealing. Increase in wheel speed improves soft magnetic and magnetoimpedance properties due to decrease in perpendicular anisotropy which is associated with stripe domain formation. On annealing soft magnetic properties and magnetoimpedance deteriorate due to the formation of crystalline phases. [Copyright &y& Elsevier]

Alloys of Tb0.3Dy0.7Fe1.95− x Ti x were vacuum induction melted and investigated for microstructural features and magnetic properties. Ti addition aids in diminishing the formation of pro-peritectic (Dy,Tb)Fe3 phase at the expense of TiFe2 phase formation. The magnetostriction was found to improve with the addition of Ti. Ti addition was also found to influence the saturation magnetization, Fe magnetic moment and Curie temperature of (Tb,Dy)Fe2 phase. [Copyright &y& Elsevier]

Abstract: Tb0.3Dy0.7Fe1.95 alloy was cast and directionally solidified by modified Bridgman technique at different solidification rates and investigated for microstructural features and magnetic properties. The phase relationship between the co-existing phases viz., (Tb,Dy)Fe2, (Tb,Dy)Fe3 and (Tb,Dy)-rich are studied as a function of solidification rate to evolve a structure–property correlation. Higher solidification rate improves <110> grain texture and favour large magnetostriction. The magnetization and Mössbauer studies indicate no perceptible change in Fe magnetic moment, with a slight deviation in the 1:3 intensity ratio of the two sextets. Comparing the Mössbauer and microstructural results a relationship has been established between the intensity ratio and the volume fraction of the deleterious minor phase (Tb,Dy)Fe3 in (Tb,Dy)Fe2 microstructure. [Copyright &y& Elsevier]

Alloys of Fe100− x Ga x [x= 17–30] were prepared and their structural and magnetic properties investigated. The microstructure of all the alloys exhibit s A2 as the main phase, while an ordered L12 phase is observed for the alloys with x ⩾25. The hyperfine field distributions derived from Mössbauer studies show DO3 type ordering for x >20 in addition to the A2 and L12 structure. Higher magnetostriction is observed for the compositions x =17 and 25. [Copyright &y& Elsevier]