Observation of Cu Spin Fluctuations in High-Tc Cuprate Superconductor Nanoparticles Investigated by Muon Spin Relaxation

Abstract

The nano-size effects of high-Tc cuprate superconductor La2−xSrxCuO4 with x = 0.20 are investigated using X-ray diffractometry, Transmission electron microscopy, and muon-spin relaxation (μSR). 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 μSR measurements revealed the slowing down of Cu spin fluctuations in La2−xSrxCuO4 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 Tc. It is indicated that reducing the particle size of La2−xSrxCuO4 down to nanometer size causes the appearance of magnetism. The magnetism enhances with decreasing particle size.

Enhancement of magnetism by tailoring synthesis conditions in electron-doped superconducting nanoparticles

“…The smaller the crystallite size, the stronger the magnetism, which means the magnetic correlation is more developed in the smaller sample. 28 It is confirmed that reducing the particle size down to nanometer sizes causes the suppression of superconductivity while strengthening the magnetism of the electron-doped cuprate superconductors. This result could suggest that there might be a competition between superconducting and magnetic states induced by nano-size effects.…”

“…These results indicate that the crystallite size can be designed by controlling the sintering and annealing temperature. 28,39 Moreover, sintering temperature plays a more important role than annealing temperature to make a bigger crystallite size.…”

“…The reduction in the particle size also tended to suppress superconductivity and induced slowing down of Cu spin fluctuations. 27,28 It is indicated that superconductivity and magnetism seem to compete due to both impurity substitution and nano-size effects. However, in the case of nano-size effects, it is still unclear whether the observation of magnetism is related to the dynamical stripe-spinning correlation 25,26,29,30 or due to surface effects that occur in nanoparticles.…”

Normal-State Transport Properties of Infinite-Layer Sr1−xLaxCuO2 Electron-Doped Cuprates in Optimal- and Over-Doped Regimes

“…Inelastic neutron scattering studies, on Pr La Ce CuO [ 49 ] and similar electron-doped compounds [ 50 ], have revealed that high energy spin excitation of such compounds are similar to those observed in anti-ferromagnetic alloys. Moreover, observations of Cu spin-fluctuations have been proved by muon spin relaxation experiments in cuprate superconductors [ 51 ]. In this respect, Rivier and Zlatic developed a model describing the resistivity of itinerant electrons scattered by localized anti-ferromagnetic spin fluctuations [ 52 ] where a linear scaling-law for the resistivity only occurs up to the so-called spin-fluctuation temperature .…”

Superconductivity in Nanosystems: A Fruitful Path to New Phenomenology in Quantum Materials

“…Firstly, two articles in this Special Issue are dedicated to some interesting interrelations between magnetic and superconducting orders that become realizable through nanoscience. Winarsih et al [ 6 ] conducted studies of nanoparticles of the La Sr CuO cuprate superconductor, observing that a reduction of the particle size down to the nanometric scale is accompanied by the appearance of magnetic correlation in the Cu spin fluctuations. They likewise observed a change in the bond distance between Cu and O ions in the conducting layer, which seems to correlate with that new magnetism.…”