Calculation of the Exchange Interaction Constant Between the Rare-Earth and the Transition Metal Sub-lattices in R₂Fe_17-xM_x(M = AI or Ga)

A precise calculation of the exchange interaction constant J_RT between the rare-earth sub-lattice and the transition metal sub-lattice in R₂Fe_17-xM_x(R: rare-earth, M = Al or Ga) compounds is given. The calculated values for Tb₂Fe_17-xGa_x(x = 6 and 7) and Dy₂Fe_17-xAl_x(x = 5, 6, 7 and 8) compounds are in excellent agreement with the values derived from the high-field measurement.