[en] An interstitial Pr₃(Fe,Ti)₂₉ hydride was synthesised by gas-phase hydrogenation on Pr₃(Fe,Ti)₂₉ powder using H₂. The reaction kinetics between Pr₃(Fe,Ti)₂₉ and H₂ gases was studied in a constant-volume reactor. The sample starts to rapidly absorb hydrogen, interstitially, at about 533 K. Absorption passes through a maximum at about 598 K (1.6 H/f.u) and then interstitial hydrogen desorption takes place up to the temperature of 673 K. By cooling to room temperature, the sample absorbs more hydrogen, interstitially, reaching the value of 3.6 H/f.u. By remaining at room temperature, the sample absorbs even more hydrogen reaching the value of 5.2 H/f.u. The lattice expansion observed is 2.1% and the Curie temperature, T_C, increased from 392 to 518 K. The hydride exhibits saturation magnetisation, M_S, of 145.4 and 157.5 Am²/kg at room temperature (RT) and at 5 K, respectively, anisotropy field, H_A, of 2.1 T (RT) and 4.5 T (5 K) and average hyperfine field, H_eff, of 23.3 T (RT). The magnetic anisotropy of Pr₃(Fe,Ti)₂₉ hydride is the same as that of the parent compounds, easy-cone-like, changing only in the cone angle (from 34 deg. to 26 deg.)

[en] The angular dependence of coercivity in a Sm(Co_0.75F_0.12Cu_0.10Zr_0.03)_7.6 alloy is studied as a function of temperature in order to probe possible indications of a change in the reversal mechanism. The results show a gradual change of the magnetization reversal mechanism from pinning (at room temperature) to nucleation (at 500 deg. C) with a mixture of both mechanisms co-existing in a large temperature range. The relatively weak angular dependence does not agree quantitatively with the degree of grain misalignment calculated by refinement of X-ray diffraction data. Possible explanations are discussed

[en] Formation and magnetic properties of the interstitial Nd₃(Fe,Ti)₂₉-type nitrides were investigated for Nd₃(Fe_1-xCo_x)_27.7Ti_1.3 over the concentration range 0< x≤0.4. The decomposition temperature T_d decreases with increasing Co content x. The relative lattice expansion upon nitrogenation is 4.6-4.9% indicating 3.5-3.7 N-atoms per formula unit. Upon nitrogenation the Curie temperature values increase with Co, but the increase rate is slower compared to that of the parent compounds. For x=0.1, 0.2 a complex magnetic anisotropy is observed, whereas, for x=0.3 and 0.4 the compounds present uniaxial anisotropy with an easy magnetisation direction along the [4 0 -2] direction. The increase of the average hyperfine field by substituting Co for Fe in Nd₃(Fe_1-xCo_x)_27.7Ti_1.3N_y is rather small and the position of the maximum (x=0.1) at room temperature is closer to Fe than for the parent compounds (at least x=0.4)

[en] Starting with the Nd₃(Fe,Ti)₂₉ stoichiometry [Tb₃(Fe_1-xCo_x)_27.4V_1.6 and Dy₃(Fe_1-xCo_x)_27.8V_1.2; x=0.6, 0.8, 1.0] two novel series of R-Fe-Co-V intermetallic compounds with a disordered variant of the hexagonal Th₂Ni₁₇-type structure were formed. The cell parameters decrease and the Curie temperature increases with increasing Co content. XRD patterns of magnetically aligned powder samples revealed the presence of a planar magnetic anisotropy

[en] ⁵⁷Fe Moessbauer spectra at 85, 200 and 293 K of magnetically aligned powders of Nd₃(Fe_1-xCo_x)_27.7Ti_1.3 (0≤x≤0.4) have been obtained. The fitting procedure has been done taking into account the occupancy of the Fe sites by Co and Ti. From the intensity ratio of the Moessbauer lines it has been concluded that the x=0 compound presents easy-cone-type anisotropy and the x=0.3, 0.4 axial anisotropy over the whole temperature range 85-293 K. For x=0.1, 0.2 a spin reorientation transition has been observed from axial anisotropy at 293 K to an easy-cone-type anisotropy at low temperatures

[en] The magnetocrystalline anisotropy of the compounds with stoichiometry Y₃Fe_27.5V_1.5(Y(Fe,V)_9.66) and Y₃Fe_27.5V_1.5N_x(Y(Fe,V)_9.66N_x) with a CaCu₅-type structure has been studied by magnetization measurements in the temperature range 5-300 K, analyzed by the Sucksmith-Thompson method, and by torque measurements at room temperature on powder samples oriented in a rotating magnetic field

[en] FePtMn nanoparticles with a narrow size distribution and an average diameter of 3 nm were synthesized by the chemical reduction of Fe(acac)₃ and Pt(acac)₂ by NaBH₄ and the thermal decomposition of Mn₂(CO)₁₀ in phenyl ether. The as-made nanoparticles have a disordered face-centred cubic (fcc) structure, which transformed after thermal treatment at 650 deg. C to an ordered face-centred tetragonal (fct) structure, possessing coercivity values up to 13.7 kOe at room temperature. The coercivity of the annealed samples depends on the amount of Mn added to the reaction mixture, with the coercive field increasing significantly with the partial substitution of Pt by Mn, while the partial substitution of Fe by Mn does not affect the magnetic properties strongly

[en] Hexagonal close-packed (hcp) Ni particles were prepared in the nanosize range (13-25 nm) by reduction of Ni(NO₃)₂ in polyethylene glycol (PEG) with various molecular weights. The reaction occurred in the presence of an equimolecular mixture of oleic acid and oleyl amine, which plays the role of a stabilizer and gives solubility to the nanoparticles in non-polar solvents. The crystal structure of Ni particles seems to be controlled by the molecular weight of the PEG molecule and subsequently the reaction temperature. The magnetic properties of the hcp Ni nanoparticles are also studied

[en] A novel phase with nominal composition Y₃Fe_27.5V_1.5 has been synthesized by arc melting elemental constituents, followed by annealing at 1123 K. The samples were analyzed by electron microprobe analysis and the stoichiometric composition was Y_3.04Fe_27.56V_1.44. X-ray diffraction from powder samples shows that the structure is of a disordered CaCu₅-type (Space Group: P6/mmm) with lattice parameters a=4.8769(1) A, c=4.1729(3) A. This disordered structure, revealed using standard difference Fourier methods, can be considered as a TbCu₇-type, containing iron dumbbell sites. The disorder is not restricted to the rare earth sites and the dumbbell atoms, but is observed at other sites as well. The stoichiometric formula derived by Rietveld analysis is Y_3.00(3)Fe_28.5(3). Magnetic measurements give a Curie temperature of 439(5) K, and a saturation magnetization of 156.4 and 125.5 A m² kg^-1 at 5 and 300 K, respectively. The anisotropy field is 4.76 T at 5 K and 2.43 T at 300 K. X-ray powder diffraction patterns of magnetically aligned powder samples indicate that the magnetocrystalline anisotropy is of easy plane type. This result is supported from the analysis of the magnetization measurements on aligned powders which give K₁<0, K₂>0 and K₁+2K₂<0, a result that confirms the easy plane anisotropy. Moessbauer spectra were also obtained and fitted with a model consistent with the disorder. The average hyperfine fields are 28.4 and 21.5 T at 4.2 and 300 K, respectively. (orig.)

[en] An element-specific study of the Nd₃Fe_27.5Ti_1.5 compound using the hard x-ray magnetic circular dichroism (XMCD) technique is presented. The Nd L₂ and L₃ edge XMCD, as well as the Fe K edge XMCD, were measured in a magnetically oriented sample, parallel and perpendicular to its alignment direction. The XMCD spectra were recorded at three different temperatures, above, below and in between the characteristic peaks that the specific compound presents in AC susceptibility measurements. By probing the Nd L edges and the Fe K edge XMCD, we found that the dipolar R(5d)-Fe(3d) exchange interaction behaves differently with temperature change than the Fe-Fe magnetic interaction. Those differences appear to be in the vicinity of the AC susceptibility characteristic peaks. An XMCD signal was recorded at the Ti K edge, revealing a small orbital polarization due to the hybridization with Fe atomic states. This demonstrates the existence of a small finite magnetic moment in Ti atoms.