Neutron scattering study of the magnetic transition in (Ho/sub 1-x/Er/sub x/)Rh4B4 alloys

Using neutron scattering techniques we have examined the magnetic transitions for compounds in the (Ho/sub 1-x/Er/sub x/)Rh4B4 pseudoternary system. We find a wide variety of behavior ranging from mean-field behavior for HoRh4B4 to complicated behavior with more than one type of ordering for Ho/sub 0.3/Er/sub 0.7/Rh4B4. Our results for the pseudoternary compounds are consistent with a model in which Ho orders along the c axis with nearly its free-ion moment, while Er orders in the basal plane, but with a moment reduced from the free-ion value. Ordering along the c axis results in the destruction of superconductivity in a sharp transition at the same temperature that a sharp spike appears in the heat capacity. Because Ho and Er have competing orthogonal magnetic anisotropies, pseudoternary compounds near the composition Ho/sub 0.3/Er/sub 0.7/Rh4B4 are near a multicritical point in the magnetic phase diagram