Ad. Shengelaya et al., DENSITY-OF-STATES AND MAGNETIC CORRELATIONS IN THE LA2-XSRXCUO4 SYSTEM STUDIED BY EPR OF FE SPIN PROBES, Physica. C, Superconductivity, 233(1-2), 1994, pp. 124-130
EPR of Fe3+ ions doped to La2-xSrxCuO4 samples with various Sr content
(x=0-0.25) has been carried out. In the high-temperature region the E
PR linewidth was determined by the Korringa relaxation. By extracting
the Korringa contribution, we were able to evaluate a dependence of th
e density of states N-F on X. It has been found that N-F continuously
grows with Sr doping from under- to overdoped regimes. The obtained N-
F(x) dependence indicates that the insulator-metal transition near x=0
.06 is driven by hole delocalization. In the low-temperature region th
e relaxation rate was determined by spin-spin relaxation. The low-temp
erature upturn observed for the temperature dependence of the EPR line
width can be understood by a slowing down of spin fluctuations due to
spin freezing and/or carrier localization. We suggest that carrier loc
alization enhancement plays an important role in the occurrence of the
well known anomaly of T-c near x = 0.125 (so-called 1/8 problem).