Magnetic ordering of Gd_xEr_1−xRh₄B₄ near the superconducting region

Gd_xEr_1−xRh₄B₄ exhibits superconductivity at some critical temperature T_c followed by the onset of long‐range ferromagnetic ordering at a lower temperature and a loss of superconductivity for x<x_c?0.28, where x_c is the critical concentration at which superconductivity is suppressed. For x above x_c, the compound is no longer superconducting but is still magnetically ordered. We have made ac resistivity R, ac magnetic susceptibility χ, and dc magnetization measurements on samples with x near x_c. For x?0.28, the salient features for the R and χ measurements are: (1) In zero external field a sharp maximum in the ac χ (T) and a minimum in R(T) are observed. With a small external dc magnetic field (∼10² Oe), the extrema in χ (T) and R(T) are depressed and smeared considerably with a corresponding shift in the temperature at which the extrema occur. (2) The sample is not superconducting down to 0.6 K. (3) In the presence of a dc magnetic field, a second ac χ peak appears at a slightly higher temperature. (4) The field dependence of the ac susceptibility resembles that of a spin glass. Details of the field dependence of these observations and the nature of these phenomena will be presented.