Magnetic ordering and spin reorientation transitions in hole-doped T′ phases Nd_2-xSr_xCuO_4-δ: A μ⁺SR study

The magnetic properties of the Nd_2-xSr_xCuO_4-δ(x=0.0-0.20) system are studied using muon spin relaxation. The Néel temperature for long range order of the Cu sublattice decreases from 260 K for the formally reduced x=0.03 sample to 60 K for the formally oxidised x=0.10 sample. The formally oxidised x=0.20 sample (4% hole doping) does not order down to 11 K but shows evidence of slowing down of the Cu²⁺ spin fluctuations. Two spin reorientation transitions are identified for low Sr²⁺ doping, with 5% Sr²⁺ doping being sufficient to suppress the transition. It appears that the destruction of magnetic long range order is a necessary but not a sufficient condition for the onset of metallic and superconducting behaviour in the layer cuprates.