Destruction of Superconductivity at the Onset of Long-Range Magnetic Order in the Compound ErRh4 B4

The compound ErRh4B4 becomes superconducting at a critical temperature T c1 of 8.7 K followed by a return to the normal state at a second critical temperature T c2 of 0.9 K. The return to the normal state at T c2 is coincident with the occurrence of long-range ordering of the magnetic moments of the Er 3+ ions which completely occupy a set of equivalent lattice sites.