Effect of Tb/Gd Substitution on Crystal Structure and Exchange Interactions of $Gd_{1 - x}Tb_{x}Ni_3$ Intermetallic Compounds

In the paper an influence of Tb/Gd substitution on crystal structure and exchange interactions of $Gd_{1 - x}Tb_{x}Ni_3$ (x = 0.0, 0.5, 0.8, 1.0) polycrystalline compounds have been studied. The crystal structure of all samples was checked at the room temperature by means of X-ray diffraction. Exchange integrals of $R-R (J_{RR}),$ $T-T (J_{TT})$ and $R-T (J_{RT})$ atoms were evaluated from M(T) magnetization curves (2-300 K, 2 T) based on the mean field theory calculation. As it was shown the samples examined are single phase and crystallize in the PuNi_3 (space group R-3m) type of crystal structure. The Tb/Gd substitution causes the decrease of lattice parameters as well as the volume of the unit cell. With increase of the x parameter the magnetic moment of Tb atoms increases from 6.94 $μ_{B}$ (x = 0.5) to 8.12 $μ_{B}$ (x = 1). The M(T) dependence of the examined compounds depends almost 8 times stronger on exchange interactions within the R-R site than the interactions between the two antiferromagnetically coupled magnetic sublattices R-T.