MOSSBAUER EMISSION MEASUREMENTS ON HIGHLY DILUTE FE-57 IMPURITIES IN THE HIGH T-C SUPERCONDUCTORS LA2-XSRXCUO4

Mossbauer emission measurements on quasi-isolated Fe-57 impurities sub stituted for Cu in La2-xSrxCuO4 show a rapid change in the local magne tic behaviour when the Sr content 2 exceeds an effective value x(t), w hich is roughly at the centre of the superconducting x range in the ph ase diagram. For x < x(t), the Fe3+ impurity systematically pins a Cu spin-glass cluster where the spins are oriented near the basal plane, with a freezing temperature of 8 +/- 1 K with respect to the character istic time scale of the Mossbauer probe. For x > x(t), the probe no lo nger detects local antiferromagnetic ordering, but it reveals the pres ence of an induced localized magnetization in the Cu sublattice, which is preferentially oriented near the (c) over bar axis for the largest x values. The results are discussed and compared with other available measurements, including our previous Fe-57 Mossbauer absorption study in the same series.