Reversible magnetization and superconducting-state thermodynamic parameters for underdopedLa1.90Sr0.10CuO4

Abstract

Magnetization studies have been made of single-crystal ${\mathrm{La}}_{1.90}{\mathrm{Sr}}_{0.10}{\mathrm{CuO}}_{4}$ with $H\ensuremath{\Vert}c$ in order to determine the magnitude of the flux expulsion and free energy in a material that has substantially less than optimal doping. Well above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below ${T}_{c},$ there is a large portion of the $H\ensuremath{-}T$ plane where the sample shows reversible behavior so that thermodynamic variables such as the free energy and the shape of the magnetization curves can be determined. At low temperature, the vortices have a well defined Abrikosov regime that transforms to two-dimensional fluctuation behavior at higher temperatures. The magnetization vs temperature curves show a unique crossing point at 22 K where the magnetization is independent of magnetic field. From this value of the crossing point, the effective layer spacing s is derived to be 1.6 nm compared to the ${\mathrm{CuO}}_{2}$ lattice spacing of 0.66 nm. The fluctuations are found to obey two-dimensional scaling in that ${M/(\mathrm{TH})}^{1/2}$ is a universal function of $[T\ensuremath{-}{T}_{c}(H)]{/(\mathrm{TH})}^{1/2}.$ Below 12 K, the data fit the Hao-Clem theory rather well and give ${\ensuremath{\kappa}}_{c}$ values of about 175 and thermodynamic critical fields ranging from 112 mT at 12 K to 133 mT at 6 K.