The magnetic orderings and phase transitions of rare-earth rhodium borides

Perturbation theory and mean-field approach have been employed in the present work to estimate the Heisenberg coupling constants 's for the ferromagnet DyRh₄B₄ and the antiferromagnet TmRh₄B₄ from their magnetic transition temperatures T_M's in comparison with GdRh₄B₄. We found that the 's of these substances are different from each other, which may be attributed to their different electronic structures and also the anisotropic nature of the Heisenberg exchange coupling.