Using techniques of microwave spectroscopy at 13 GHz, we have observed antiferromagnetic resonance arising from the magnetically ordered cuprate planes of conducting Pr Ba2 Cu4 O8; the Cu Néel temperature is approximately 80 K. In addition, we have detected a Cu electron spin resonance which is due either to Cu in chain fragments or more likely to Cu in a minority impurity phase, BaCu O2, a phase also detected by x-ray diffraction. Although this sample was conducting to the lowest temperatures, no indication of even granular superconductivity was detected. The c-axis parameter of Pr Ba2 Cu4 O8 is dependent on processing and varies more than in other Ln124 materials; we propose that the lack of superconductivity is a consequence of a defect, namely, substitution of a variable content of smaller Pr on the Ba site. Such substitution also results in the formation of the minority phase BaCu O2. Our observation of cuprate-plane antiferromagnetism coupled with evidence that the cuprate planes are insulating (provided by Horii [Phys. Rev. B 6, 6327 (2000)]) indicates that any conductivity is associated with the CuO chains, not with the Cu O2 planes. These results imply that the existence of the pseudogap detected at 150 K in Pr124 by Bäckström [Phys. Rev. B. 61, 7049 (2000)] is unrelated to either carriers or spin fluctuations in the cuprate planes.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2007 Jul 30
ASJC Scopus subject areas
- Condensed Matter Physics