ABSTRACT
This paper presents the synthesis of Fe-Co-Ni nanocomposites by chemical precipitation, followed by a reduction process. It was found that the influence of the chemical composition and reduction temperature greatly alters the phase formation, its structures, particle size distribution, and magnetic properties of Fe-Co-Ni nanocomposites. The initial hydroxides of Fe-Co-Ni combinations were prepared by the co-precipitation method from nitrate precursors and precipitated using alkali. The reduction process was carried out by hydrogen in the temperature range of 300-500 °C under isothermal conditions. The nanocomposites had metallic and intermetallic phases with different lattice parameter values due to the increase in Fe content. In this paper, we showed that the values of the magnetic parameters of nanocomposites can be controlled in the ranges of MS = 7.6-192.5 Am2/kg, Mr = 0.4-39.7 Am2/kg, Mr/Ms = 0.02-0.32, and HcM = 4.72-60.68 kA/m by regulating the composition and reduction temperature of the Fe-Co-Ni composites. Due to the reduction process, drastic variations in the magnetic features result from the intermetallic and metallic face formation. The variation in magnetic characteristics is guided by the reduction degree, particle size growth, and crystallinity enhancement. Moreover, the reduction of the surface spins fraction of the nanocomposites under their growth induced an increase in the saturation magnetization. This is the first report where the influence of Fe content on the Fe-Co-Ni ternary system phase content and magnetic properties was evaluated. The Fe-Co-Ni ternary nanocomposites obtained by co-precipitation, followed by the hydrogen reduction led to the formation of better magnetic materials for various magnetically coupled device applications.
ABSTRACT
The calculation of the heat of formation of Sm(Co1-x-y Fe x Ni y )5 compound using homemade software in the framework of Miedema's model was carried out. In addition we investigated the influence of the probability of occupation the transition metals sites by 3d-ions, in particular, equiprobable distribution of 3d-ions among 2c and 3g sites and selective distribution Co/Ni-(2c), Fe-(3g). The maximal Fe and Ni doping ranges, where Sm(Co1-x-y Fe x Ni y )5 phase with the CaCu5-type crystal structure stable, were estimated for both types of distribution. The corresponding values of the number of 3d-electrons per atom were 7.23 (Fe/Co/Ni-(2c, 3g)) and 7.3 (Co/Ni-(2c), Fe-(3g)). Based on calculation the Sm(Co1-x-y Fe x Ni y )5 (x = 0.15, 0.3, 0.45; y = 0.05, 0.1, 0.15) melt-spun ribbons were synthesized. The maximal doping level of x = 0.5 and y = 0.2 was experimentally determined for Fe and Ni atoms, respectively. These values are in good agreement with the theoretical prediction, assumed equiprobable distribution of 3d-ions among transition metal sites. The best among the series in terms of energy product Sm(Co0.6Fe0.3Ni0.1)5 sample possesses a coercivity of 10.9 kOe and remanent magnetization of 51 emu g-1.
ABSTRACT
Exchange-coupled nanocomposites are considered as the most promising materials for production of high-energy performance permanent magnets, which can exceed neodymium ones in terms of energy product. In this work, micromagnetic simulations of L10-FeNi/SmCo5 composites based on the initially anisotropic structure of nanorods array were performed. Texturing effect on magnetic properties was investigated. It was revealed that even 30% of anisotropy axes misalignment of grains in L10-FeNi phase would lead to only ≈10% drop of coercivity. To maximize magnetic properties of the composites, parameters of microstructure were optimized for 120 × 120 array of interacting nanorods and were found to be 40 nm nanorod diameter and 12-20 nm interrod distance. The estimated diameter of nanorods and the packing density of the array provide energy product values of 149 kJ m-3. Influence of interrod distance on energy product values was explored. Approaches for production of exchange-coupled composites based on anisotropic nanostructures were proposed.
