Observation of Cu Spin Fluctuations in High- T c Cuprate Superconductor Nanoparticles Investigated by Muon Spin Relaxation.

The nano-size effects of high- T c cuprate superconductor La 2 - x Sr x CuO 4 with x = 0.20 are investigated using X-ray diffractometry, Transmission electron microscopy, and muon-spin relaxation ( μ SR). It is investigated whether an increase in the bond distance of Cu and O atoms in the conducting layer compared to those of the bulk state might affect its physical and magnetic properties. The μ SR measurements revealed the slowing down of Cu spin fluctuations in La 2 - x Sr x CuO 4 nanoparticles, indicating the development of a magnetic correlation at low temperatures. The magnetic correlation strengthens as the particle size reduces. This significantly differs from those observed in the bulk form, which show a superconducting state below T c . It is indicated that reducing the particle size of La 2 - x Sr x CuO 4 down to nanometer size causes the appearance of magnetism. The magnetism enhances with decreasing particle size.