Tailoring the structural and magnetic properties of sol-gel derived Sm-Co nanogranular films

In this study, we investigated the microstructure, phase evolution and magnetic properties of nanogranular films of Sm-Co compounds processed by the sol-gel method. By controlling the compositional ratio of Sm:Co precursor concentration, nanogranular films consisting of three distinct hard magnetic phases namely, Sm₂Co₇, SmCo₅ and Sm₂Co₁₇ with coercivity values of 1.78, 2.94 and 2.12 kOe, respectively, were obtained through this technique.     

The influence of pH and bath composition on the properties of Fe-Co alloy film electrodeposition

Fe-Co films were electrodeposited on ITO glass substrates from the electrolytes with different molar ratio of Co²⁺/Fe²⁺ and different pH values (2.1, 2.9, 3.7, and 4.3) at 25 °C. The properties of Fe-Co alloy films depend on both Co²⁺ and Fe²⁺ concentrations in electrolyte and pH values was studied. The content of Co increases from 40% to 85% as the mole ratio of CoSO₄/FeSO₄ increasing from 0.50/0.50 to 0.90/0.10 in electrolyte and slightly decreases from 77% to 63% as the pH values increasing from 2.1 to 4.3. The X-ray diffraction analysis reveals that the structures of the films strongly depend on the Co content in the binary films. The surface morphologies of the films are influenced by the combined action of composition and phase structure. The saturation magnetization reaches a maximum value of 2974.03 emu/cm³ and coercivity reaches a minimum value of 42.72 Oe of the Fe_0.30Co_0.70. The saturation magnetization reaches a maximum values of 2974.03 emu/cm³ and coercivity reaches a minimum values of 42.72 Oe of the Fe_0.30Co_0.70 at pH = 2.9.     

Preparation and magnetic properties of anisotropic (Sm,Pr)Co5/Co composite particles

Anisotropic (Sm,Pr)Co₅/Co nanocomposite particles have been fabricated by chemical coating the 2 h ball milled (Sm,Pr)Co₅ flakes with Co nanoparticles. The Co nanoparticles were synthesized with mean particle sizes in the range of 20-50 nm. The nanocomposite particles present [0 0 1] out-of-plane texture and improved magnetic properties, e.g., an enhanced remanent magnetization of 72 emu/g for (Sm,Pr)Co₅/Co and 66 emu/g for (Sm,Pr)Co₅. In addition, by using the 8 h ball milled powders (much smaller than the 2 h ball milled powders) as the starting materials, Co nanoparticles can also be successfully coated on the surface of the flakes. A plausible mechanism for the formation of Co nanoparticles on the surface of (Sm,Pr)Co₅ flakes is discussed.     

Magnetic properties of cobalt substituted M-type barium hexaferrite prepared by co-precipitation

The co-precipitation and solid state methods were used in the synthesis of barium hexaferrite (BaM). Phase pure BaM was obtained with 1, 2, 3, 5, 10, 15, 20 and 30 wt% cobalt oxide (Co₃O₄). The addition of Co^2+/3+ ions to the BaM increased the permeability and magnetic loss tangent to a value of 3.5 at 5% and reduced to 1 at 30% doping. With increased Co doping, M_s was reduced from 87-58 emu/g, M_r increased from 11 to 40 emu/g with 3–5 wt% Co and 9 emu/g for 30% doping. H_c sharply increased from 540 to 2200 Oe with a reduction to 280 Oe at 10 K with increasing temperature to 300 K. T_c increased from 740 to 750 K for 30% Co doping. DTA–TGA studies of green body showed decarboxilation to occur at around 825 °C and the transformation of residual Co₃O₄ to Co₂O₃ at around 577 °C. The XRD data confirmed the Co ions substituting into Fe sites until a 10–15% doping level where the structure altered to W-type hexaferrite. The densities of the compounds varied with doping to a maximum of 4.45 g/cm³.     

Effect of annealing on phase composition,structural and magnetic properties of Sm-Co based nanomagnetic material synthesized by sol-gel process

Sm-Co based nanomagnetic material was synthesized by means of a Pechini-type sol-gel process. In this method, a suitable gel-precursor was prepared using respective metal salts and complexing agent such as citric acid. The gel-precursor was dried at 300 °C and then subjected to various reductive annealing temperatures: 350, 500 and 600 °C. The nanopowders so obtained were characterized for their structure, phase composition and magnetic properties. FT-IR studies on the gel-precursor showed the binding of metal cations with the citrate molecules in the form of metal-citrate complex. The gel-precursor, which was annealed at 350 °C showed the presence of both meta-stable cobalt carbide (Co₂C, Co₃C) and Co₃O₄ phases; while the sample annealed at 500 °C indicated the sign of SmCo₅ phase. Upon increasing the reductive annealing temperature to 600 °C, crystalline phase such as fcc-Co and Sm₂C₃ were formed prominently. FE-SEM analysis revealed the change in sample morphology from spherical to oblate spheres upon increasing the annealing temperature. VSM measurements demonstrated ferromagnetic nature at room temperature for all the nanopowders obtained irrespective of their after reductive annealing temperature.     

Deformation-induced texture in nanocrystalline 2:17, 1:5 and 2:7 Sm-Co magnets

The effect of crystal structures on texture induced by hot plastic deformation was studied for Sm-Co, Sm-Zr-Co, Sm-Zr-Co-Fe and Sm-Co-Fe-Mn nanocrystalline alloys with 9-22 at% Sm. Nanocrystalline precursors were obtained via high-energy ball milling and subsequent hot consolidation; deformation was carried out at 800-1150 °C. The analysis of X-ray diffraction and magnetic measurements showed that the degree of the axial [0 0 1] texture after deformation was negligible for the ordered 2:17 structure, but became increasingly noticeable for the disordered 2:17 (“1:7”), 1:5 and 2:7 structures. Because of interplay of several factors including the [0 0 1] texture, saturation magnetization and magnetocrystalline anisotropy, there was no universal trend in the hard magnetic properties with the Sm content. Optimum compositions for the maximum energy product varied from Sm₁₁(Co, Fe, Mn)₈₉ in the Sm-Co-Fe-Mn series to Sm₁₁Zr₂(Co, Fe)₈₇ in the Sm-Zr-Co-Fe series to Sm₁₇(Co, Fe)₈₃ in the Sm-Co-(Fe) series. Iron substitution for cobalt strongly suppresses the 1:5 structure, whereas the Fe-free magnets based on the SmCo₅ compound showed by far the highest room-temperature coercivity.     

Ni–Zn–Sm nanopowder ferrites: Morphological aspects and magnetic properties

Ni–Zn ferrites have been widely used in components for high-frequency range applications due to their high electrical resistivity, mechanical strength and chemical stability. Ni–Zn ferrite nanopowders doped with samarium with a nominal composition of Ni_0.5Zn_0.5Fe_2−xSm_xO₄ (x=0.0, 0.05, and 0.1 mol) were obtained by combustion synthesis using nitrates and urea as fuel. The morphological aspects of Ni–Zn–Sm ferrite nanopowders were investigated by X-ray diffraction, nitrogen adsorption by BET, sedimentation, scanning electron microscopy and magnetic properties. The results indicated that the Ni–Zn–Sm ferrite nanopowders were composed of soft agglomerates of nanoparticles with a high surface area (55.8–64.8 m²/g), smaller particles (18–20 nm) and nanocrystallite size particles. The addition of samarium resulted in a reduction of all the magnetic parameters evaluated, namely saturation magnetization (24–40 emu/g), remanent magnetization (2.2–3.5 emu/g) and coercive force (99.3–83.3 Oe).     

Structure and magnetic properties of SmCoxTi0.4-1:7 ribbons

SmCo_xTi_0.4 (x=6.6, 7.1, 7.6, 8.1) ribbons have been prepared by melt spinning at a wheel speed of 42 m/s, followed by annealing at 750 °C for 2 h. Both as-spun and as-annealed ribbons possess the disordered TbCu7-type (1:7) phase even when the Sm/(Co,Ti) atomic ratio deviates from 1/7. The c/a ratio increases with increasing Co concentration x, but the unit cell volume decreases. The Curie temperatures show above 700 °C, increasing from 707 °C for x=6.6 to 782 °C for x=8.1. The saturation magnetizations increase almost linearly with increasing Co content. The observed magnetic hardening is believed to arise from the high magnetocrystalline anisotropy of the 1:7 phase and the fine nanograin structure. The intrinsic coercivity of 9797 Oe has been obtained in the melt-spun SmCo_7.1Ti_0.4 ribbons.     

Soft magnetic properties of FeCo films with Co underlayer

Bilayered Fe₆₅Co₃₅ (=FeCo)/Co films were prepared by facing targets sputtering with 4πM_s∼24 kg. The soft magnetic properties of FeCo films were induced by a Co underlayer. H_c decreased rapidly when the Co underlayer was 2 nm or more. The films showed well-defined in-plane uniaxial anisotropy with the typical values of H_ce=10 Oe and H_ch=3 Oe, respectively. High frequency characteristics of the films show the films can work at 0.8 GHz with real permeability as high as 250.     

Preparation and properties of cobalt oxides coated carbon fibers as microwave-absorbing materials

Cobalt oxides/carbon fibers (CoO_x/CFs) composites were synthesized by thermal oxidation of cobalt coated carbon fibers (Co/CFs). The scanning electron microscopy images and X-ray diffraction pattern indicate that the layers are about 0.7 μm and composed of Co₃O₄ and CoO (CoO_x), the preferred condition for preparation of CoO_x/CFs composites is to anneal Co/CFs precursors at 350 °C for 3 h in air. The coercivity, saturation magnetization and residual magnetization of the CoO_x/CFs composites are 464.8 Oe, 10.62 emu/g and 2.21 emu/g, respectively. The reflectivity of cobalt oxides coated carbon fibers (1.11-5.12 mm in thickness) is less than −10 dB over the working frequency range of 4.04-18.00 GHz and less than −20 dB over 11.54-14.77 GHz. The lowest reflectivity is −45.16 dB at 13.41 GHz when the thickness is 1.50 mm.