Determination of the intersublattice exchange interactions in GdCo12-xFexB6 (x = 0-3) intermetallic compounds by high field magnetization measurements

High field magnetization measurements up to 60 T on free powder samples from GdCo12-xFexB6 (x = 0-3) compounds are reported. The data were used to evaluate the microscopic exchange interaction integral, JGd-3d, between Gd and 3d (Co,Fe) spins. The systems are ferrimagnets; they order magnetically between TC = 95 K for x = 3 and TC = 165 K for x = 0. The low temperature magnetization curves as well as the temperature dependence of intrinsic magnetic parameters are determined by magnetic measurements in pulsed magnetic field. The average magnetic moment ⟨μCo+Fe⟩ per mean transition metal atom (Co + Fe) is small and increases with increasing Fe concentration from 0.44 μΒ for x = 0 to 0.51 μΒ for x = 3 at T = 4 K. From high field magnetization curves, a value of JGd-3d/kB = −4.65 K is derived for x = 0, whereas mean field approximation yields a much larger 3d-3d exchange integral of JCo-Co/kB = 105 K. The obtained results reveal an increase of −JGd-3d/kB with Fe concentration. For x = 0.5, the intersublattice coefficient nGd-3d is found to keep an almost constant value of 5.87 ± 0.13 T*f.u.*μB−1 whatever the temperature in the 2 to 60 K range.