Effect of Ni doping on stabilization of Sm(Co_1-xFe_x)₅compound: thermodynamic calculation and experiment

The calculation of the heat of formation of Sm(Co_1-x-yFe_xNi_y)₅compound 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(Co_1-x-yFe_xNi_y)₅phase 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(Co_1-x-yFe_xNi_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 ofx= 0.5 andy= 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(Co_0.6Fe_0.3Ni_0.1)₅sample possesses a coercivity of 10.9 kOe and remanent magnetization of 51 emu g^-1.