Anomalous Temperature Dependence of139La Nuclear Spin-Lattice Relaxation in La2CuO4-δand (La0.9Ca0.1)2CuO4-δ

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Abstract
Nuclear spin-lattice relaxation time ( T 1 ) of 139 La in the antiferromagnet La 2 CuO 4-δ and the superconductor (La 0.9 Ca 0.1 ) 2 CuO 4-δ has been measured in a zero applied field and temperature ranges of 1.7 K–299 K and 1.8 K–130 K, respectively. A divergent behavior of the relaxation rate (1/ T 1 ) toward the Néel temperature ( T N ≃250 K) which is characteristic of itinerant antiferromagnets has been observed in La 2 CuO 4-δ above T N ≃70 K. An anomalous enhancement of 1/ T 1 ( T ) below about 70 K has been observed in both oxides. Because of this unclarified enhancement, the change of 1/ T 1 ( T ) which is associated with the superconducting transition was not observed in (La 0.9 Ca 0.1 ) 2 CuO 4-δ below T c ≃18 K.