Magnetic measurements of the lower critical fields and irreversible properties of oxygen deficient YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} single crystals

Abstract

We present results for lower critical field, irreversibility field and hysteresis on an oxygen deficient single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} annealed to a {Tc} of 28 and 85 K. We compare results for off-plateau ({Tc} = 28 and {Tc} = 85 K) stoichiometries to earlier results on the 60 K {Tc} plateau crystals and the fully oxygenated 92 K {Tc} crystals. We find a systematic decrease in the lower critical field with decreasing {Tc}, and a decrease in the remanent magnetization by a factor of 10, at T = 5 K, for the {Tc} = 28 K phase compared to the {Tc} = 85 K phase. Our irreversibility field versus reduced temperature data indicate much stronger curvature and hence a larger reversible region for the reduced oxygen stoichiometries. For crystals with {Tc} = 62.2, 56, 50, and 28 K, a crossover occurs in the slope of log(H{sub irr}) vs log(l-T/{Tc}). The field at which this crossover occurs is lower for the more oxygen deficient phases and may be linked to their lower H{sub c1} values and corresponding longer penetration depths.