[en] The alloy of TbFe₂ was studied by ball milling with and without the presence of external magnetic field. While the structure and powder morphology of the alloy were investigated using scanning electron microscope and X-ray diffraction, the magnetization was investigated using vibrating sample and superconducting quantum interference device magnetometers. The rate of particle reduction with ball milling is comparatively higher in the presence of external magnetic field than without it. Consequently, owing to a large fraction of particles acquiring near single domain configuration under the field assisted milling condition, the coercivity derived from these particles are as high as 6500 Oe than that of particles obtained without the aid of external magnetic field which is around 3850 Oe. The field cooled low temperature magnetization exhibits a large coercivity and skew in the shape of the magnetization curve due to the large anisotropy. - Highlights: • Magnetic field assisted milling aids particle size reduction considerably. • Μagnetic field assisted milled samples exhibit a remarkable improvement in coercivity. • Εffect of agglomerations of particles on coercivity was studied

[en] The anisotropy compensated Tb_0.3Dy_0.7Fe_1.95 serves as an ideal alloy system to study the effect of microstructural refinement influencing coercivity. The cast alloy was melt spun and ball milled (with and without magnetic field) to impart microstructural refinement and correlated with the development of coercivity. Coercivity as high as 6500 Oe obtained during magnetic field assisted ball milling due to fine particle size, alignment of particles and strain. Coercivity of 1000 Oe obtained during melt spinning due to fine grain size and attacking faults on account of fast cooling. A comparative study highlighting coercivity mechanisms in the samples prepared by different routes has been highlighted in this paper

[en] The anisotropy compensated Tb_0.3Dy_0.7Fe_1.95 alloy was investigated in as-cast, directionally solidified, melt-spun and ball milled to nano size scale with an emphasis on coercivity development in all forms. For structural elucidation, scanning electron microscopy and transmission electron microscopy were employed. Large increase in coercivity has been observed for the alloy in ball milled condition, accompanied with low magnetization value. The microstructural investigations indicate that the finer grain size and the strain associated with large defect density concentration seems to be the reason for coercivity enhancement in the nano-sized powder. (author)

[en] Alloys of Dy_0.7Tb_0.3Fe_1.95-xNb_x (x = 0, 0.025, 0.05 and 0.075) were prepared in vacuum employing an induction furnace and investigated for the magnetic properties and microstructural features. A significant improvement in the magnetostriction has been obtained for the alloys containing Nb as compared to that of the parent alloy (x = 0). The Curie temperature and the Fe hyperfine field of the (Tb,Dy)Fe₂ phase are nearly invariant despite Nb addition to the parent alloy. The microstructural features, on the other hand, indicated that another Laves phase, NbFe₂ is formed as the primary phase at the expense of the undesired (Tb,Dy)Fe₃ phase. From the Moessbauer studies also the formation of NbFe₂ phase has been evidenced.

[en] Alloys of Fe₇₇Ga₂₃B_x (x=0, 0.025, 0.050, 0.075 and 0.1) were heat treated at 1000 ^oC/10 h and characterized for microstructural features and magnetostriction. The study indicates that the parent alloy consists of three phases viz. A2 as the major phase and L1₂ and DO₃ as minor phases. However, the volume fraction of L1₂ and DO₃ decreases with B addition and as a result magnetostriction improves. The decrease in volume fraction of these phases is attributed to B-segregation to the grain boundary, which seems to prevent the formation of these phases. The alloy with x=0.1, however, exhibits an additional Fe₂B phase and consequently its presence leads to the re-emergence of the DO₃ phase, affecting the magnetostriction.

[en] The structural and magnetic properties of Fe_100-xGa_x (x = 17, 20, 23, 25, 27 and 30) in heat treated (950 deg. C/10 h) and quenched condition were studied. While the X-ray diffraction patterns and the microstructures indicate that all the alloys contain only the disordered α-Fe (A2 phase), whereas, the Moessbauer spectra reveal that the alloys with x ≥ 25 contain minor fractions of ordered L1₂ and DO₃ phases. The room temperature saturation magnetostriction increases for the initial concentrations of Ga (x = 17-23) and then decreases for higher concentrations. The effect of quenching in suppressing the formation of ordered phases (L1₂ and DO₃) and in retaining the high temperature disordered (A2) phase is attributed to be the main reason for the increase in the magnetostriction due to Ga addition.

[en] Alloys of nominal composition Y_1-xEr_xFe₂ (x=0, 0.25, 0.5, 0.65, 0.75 and 1) have been prepared and investigated for the structural and magnetic properties. The microstructural features of the samples indicate that (Y,Er)Fe₂ is the main phase, with the co-existence of a minor phase (Y,Er)Fe₃, in different morphologies. The lattice parameter of the main phase is found to decrease, while the Curie temperature is found to increase with Er addition. Compensation in the temperature dependence of magnetization is, however, observed for compositions x=0.5, 0.65, 0.75 and 1. The ⁵⁷Fe-Moessbauer spectra obtained at 300 K for the samples display a superposition of two six-line patterns in the intensity ratio 1:3, thus indicating that the easy direction of magnetization lies along [1 1 1] crystallographic direction. The average hyperfine fields are found to increase marginally with Er addition, implying an enhancement in the Fe magnetic moment. The Er-Fe interaction is attributed to be the main reason for the marginal increase in the hyperfine fields and in the Curie temperature of Er-added alloys

[en] Alloys of Ho_1-xTb_xFe_1.95 (x=0, 0.15, 0.25, 0.5, 0.75 and 1) were prepared and investigated for structural and magnetic properties. The microstructure of the alloys investigated consists of three phases viz. RFe₂ as major phase, RFe₃ and R-rich as minor phases. The RFe₃ phase, however, appears in minimum volume fraction for concentrations up to x<0.25 and progressively increases with Tb addition. The lattice parameter, Curie temperature, saturation magnetization, Fe hyperfine field, coercivity and spontaneous magnetostriction are also found to increase with Tb addition. A spin reorientation transition from [1 0 0] easy direction of magnetization to [1 1 1] easy direction of magnetization was observed from Moessbauer and X-ray diffraction studies.

[en] Structure, microstructure and magnetocaloric effect were investigated in Gd_1-xGa_x (0.45 ≤ x ≤ 0.55) alloys. Phase identification and compositional analysis revealed that all these alloys consist of orthorhombic GdGa major phase with small fraction of tetragonal Gd₃Ga₂ and hexagonal GdGa₂ secondary phases for Ga-lean and Ga-rich compositions respectively. The magnetic transition temperatures (T_C) of the alloys were determined from AC susceptibility curves and it was found to be in the range of 181–186 K. Among these alloys, a maximum values of magnetic entropy change (ΔS_M)_max of 5.1 J kg⁻¹-K, adiabatic temperature change (ΔT_max) of 4.6 K and refrigerant capacity (RC) of 644 J kg⁻¹ were obtained in the x = 0.50 alloy. (paper)

[en] Highlights: ► Vol. fraction of (Tb,Dy)Fe₃ is minimum at x = 0.4 and maximum at x = 0.6 composition. ► Widmanstatten precipitate forms in the x ⩽ 0.5 alloys and is absent for x > 0.5 alloys. ► Phase field of (Tb,Dy)Fe₂ extends towards rare earth-rich side for x ⩽ 0.5 alloys. ► Phase field of Laves phase shifts towards Fe-rich side with Tb addition. ► λ Increases with Tb addition and slope of the λ–H curve is maximum for x = 0.4 alloy. - Abstract: The effect of Tb/Dy ratio on the structural and magnetic properties of (Tb,Dy)Fe₂ class of alloys has been investigated using nine alloys of Tb_xDy_1−xFe_1.95 (x = 0–1) covering the entire range. Our results indicate that the three phases viz. (Tb,Dy)Fe₂ (major phase), (Tb,Dy)Fe₃ and (Tb,Dy)-solid solution (minor phases) coexist in all the alloys. The volume fraction of pro-peritectic (Tb,Dy)Fe₃ phase however, has a minimum at x = 0.4 and a maximum at x = 0.6 compositions. The volume fraction of this phase decreases upon heat treatment at 850 °C and 1000 °C. A Widmanstatten type precipitate of (Tb,Dy)Fe₃ was observed for Dy-rich compositions (0 ⩽ x ⩽ 0.5). The microstructural investigations indicate that the ternary phase equilibria of Tb–Dy–Fe are sensitive to Tb/Dy ratio including the expansion of (Tb,Dy)Fe₂ phase field which is in contrast to the pseudo-binary assumption that is followed in available literature to date. The lattice parameter, Curie temperature and coercivity are found to increase with Tb addition. Split of (4 4 0) peak of (Tb,Dy)Fe₂ observed in x ⩾ 0.3 alloys indicate, a spin reorientation transition from [1 0 0] to [1 1 1] occurs with Tb addition.