EXCHANGE COUPLING IN GDM COMPOUNDS

The magnetic susceptibility of ferromagnetic GdM alloys (M=Cu1-xGax, M g, Zn) has been investigated under helium gas pressure for temperature s above T-C. The evaluated pressure derivatives of tile paramagnetic C urie temperature, d ln Theta/dP, appeared to be remarkably different f or isovalent GdMg and GdZn compounds (-11.2 and -0.1 Mbar(-1), respect ively). An analysis of the obtained d ln Theta/dP values for GdCu1-xGa x alloys and results of ab initio electronic structure calculations ha ve revealed the essential role of 5d electrons as tile mediators of ex change coupling in ferromagnetic GdM compounds. The pressure derivativ es of T-C were calculated by employing the modern mean-field theory, a s well as the spin-fluctuation model. As a result, good agreement is f ound with the experimental values of d ln Theta/dP.