Magnetic Phase Transitions in 90 K Superconductors HoBa₂Cu₃O_7-δ and GdBa₂Cu₃O_7-δ Observed by ZF- µ⁺SR

Abstract

Freezing of holmium magnetic moments was observed below 3 K in a 90 K superconductor HoBa 2 Cu 3 O 7-δ by zero-field positive muon spin relaxation (ZF-µ + SR) measurements. The ZF-µ + SR function revealed a marked change of µ + local field from a critically fluctuating regime (4–7 K) to a quasi-static regime below 3 K (of nearly Gaussian distribution). The observation indicates that holmium magnetic moments are short-range ordered around 2 K. In contrast, a 90 K superconductor GdBa 2 Cu 3 O 7-δ showed a zero-field spin precession at 2 K, indicating long-range ordering of gadolinium magnetic moments.