Anomalous temperature dependence of the upper critical fields in magnetic-superconducting Y 1−xGd xRh 4B 4

Abstract

We report that the dominant mechanism governing the upper critical field H c2 in Y 1−xGd xRh 4B 4 with x ≥ 0.1 is the magnetic exchange field of Gd spins. The H c2 vs. temperature curve determines the magnetic structure to be of spin glass for x = 0.1 and ferromagnetic for x ≥ 0.2.