Impurities and Nuclear Spin Relaxation in Aluminum

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Abstract
Both positive- and negative-temperature nuclear spin distributions are used to study the nuclear spin-lattice relaxation in zero external field at liquid helium temperatures in aluminum with controlled impurity content. The relaxation shows considerable deviation from previous theoretical predictions, which were based on the assumption of a single nuclear spin temperature. Most of the deviation is removed by introducing strong impurity effects at zero field, which result in cross relaxation within the nuclear spin system. In addition, the magnetic-field dependence of the relaxation is measured, and the results are compared to theoretical predictions.