| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Takao INSTITUTE OF MATERIALS RESEARCH TOHOKU UNIVERSITY RESEARCHER, 金属材料研究所, COE研究員
SASAKI Takahiko INSTITUTE OF MATERIALS RESEARCH TOHOKU UNIVERSITY RESEARCH ASSOCIATE, 金属材料研究所, 助手 (20241565)
GOTO Takayuki INSTITUTE OF MATERIALS RESEARCH TOHOKU UNIVERSITY RESEARCH ASSOCIATE, 金属材料研究所, 助手 (90215492)
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| Research Abstract |
La_<2-x>Sr_xCuO_4 shows local minimum of T_c and a magnetic ordering around x-1/8. The relation between superconductivity and the magnetic order is strongly interested. In this project the magnetic order and field induced phase transition of the spin structure was investigated in La_<2-x>Sr_xCuO_4(x-1/8). Magnetic superlattice peaks have been observed in elastic neutron-diffraction measurements on orthorhombic La_<188> CuO_4 at reciprocal points of (l/2*epsilon1/2,0), and (1/2,1/2*epsilon, 0), in the tetragonal notation, suggesting a modulated antiferromagnetic order with the incommensurability epsilon-0.126 similar to the case of La_<1.48>Nd_<0.40>Sr_<0.12>CuO_4 observed by Tranquada et. al. in the low-temperature tetragonal (TLT) phase. It is revealed from La-NMR experiments on La_<2-x-y>Y_ySr_xCuO_4 that the direction of the ordered spin in the orthorhombic (OMT) phase is along (0, *1<minus-plus>delta*delta)_0 in the orthorhombic notation where delta<<1 both for antiferromagnetic La
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_<22-y>Y_yCuO_4 and for modulated magnetic ordering La_<2-x-y>Y_ySrxCuO4(x-1/8), on the other hand, in the TLT phase the direction of the ordered spin is along (*1, *1,0)_0. When the magnetic field is applied along (0,1,0)_0 in the OMT phase, spin-flop from (0,1*1<minus-plus>delta, *delta)_0 to (*1, <minus-plus>delta, 0,0)_0 occurs at a field of 6-12 T.In the case of La_<1.88>Sr_<0.12>CuO_4 where the instability of the OMT structure glows at lower temperatures below 15 K, the spin-flop to (*1, *1,0)_0 is observed with an elastic anomaly due to the structural change from the OMT to the ThT phase. The magnetic moment of ordered Cu-3d spin and volume percentage of the magnetic ordered state is estimated from the analysis of the resonance peak width of La-NMR of La_<1.88>Sr_<0.12>CuO_4 at 4.2 K to be mu_<cu> -0.32 mu_B and -100%, respectively. Elastic constants of the flux-line lattice is also measured and volume percentage of the superconducting state is estimated to be larger than 90%, therefore, superconductivity coexists with the magnetic order microscopically over the almost whole part of the Sr_<0.12>CuO_4 crystal. The superconducting fluctuation reveals to be very small compared with an optimally doped sample (chi-0.15) especially at lower temperatures. Less
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