Paramagnetic Resonance Studies of Phase Separation in Cuprate Superconductors
Using paramagnetic resonance techniques phenomena are identified in La2CuO4+δ ceramics which support the phase separation model. A signal near B = 0, proportional to the superconducting volume fraction, decreases after heating to T i ≥ 270 K and fast quenching to 4.2 K and a new signal, related to Cu2+, appears. The initial intensities are approached under annealing at T an ≥ 200 K. In single crystal La2CuO4+δ the Cu2+ related signal is not observed. La2−x Sr x CuO4+δ ceramic does not show any of the indicated responses. The effects can be attributed to evaporation of spin polarized clusters from a percolating network of metallic - and below T c superconducting - paths under heating and subsequent quenching and condensation into such paths under annealing. The origin of the Cu2+ related signal is discussed.
KeywordsElectron Paramagnetic Resonance Excess Oxygen Isochronal Anneal Signal Height Diamagnetic Susceptibility
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