Antiferromagnetism and superconductivity: Cuprate plane magnetic ordering in YSr2Cu2.1Nb0.9O8−δ

Abstract

YSr2Cu2.1Nb0.9O8−δ, prepared using a high-pressure, high-temperature process, has been studied using superconducting quantum interference device magnetometry, neutron diffraction, and electron spin resonance (ESR). This material, in which Cu is the only magnetic ion, shows two magnetic transitions below room temperature, at 257 and 27K. While neutron diffraction fails to find antiferromagnetic Bragg peaks, ESR unambiguously shows that the compound is antiferromagnetic. Antiferromagnetic resonance is observed for temperatures below to slightly above the lower ordering temperature. The magnetization data can be understood as arising from ferromagnetic CuO2 planes, which are coupled as (independent) antiferromagnetic bilayers at the upper transition and then subsequently show full, three-dimensional order at the lower transition. This lightly hole-doped material shows a small diamagnetic response, closely coincident with the lower magnetic transition. The difference in field-cooled and zero-field-cooled magnetization curves is attributed to metamagnetism, arising from the weak coupling of the cuprate plane bilayers. The field-cooled magnetization data are strikingly similar to that reported for the so-called “ferromagnetic” superconductor GdSr2Cu2RuO8, for which the anomalous magnetization has been attributed to Ru moment canting. The absence of any magnetic ion other than Cu in this compound excludes that explanation.

Source-reported materials — not catalogue approval

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