Magnetic penetration depth of (La1-xSrx)2CuO4 single crystals

We have performed magnetization measurements on a series of high-quality, large single crystals of (La1-xSrx)2CuO4 over a composition range of x=0.05-0.10, with magnetic fields parallel to the c axis. In order to avoid the large fluctuation effects near Tc in the analysis of the magnetization of these layered superconductors, a method of data analysis, based on the variational model developed by Hao and Clem, is used for the determination of the magnetic penetration depth λab(T) of this family. The conventional London approximation for the determination of λ(T) from mixed-state magnetization isotherms M(H,T) is also reevaluated, and found generally to overestimate λab(T) of (La1-xSrx)2CuO4 by as much as 20%. Our derived values of λab(0) by the Hao-Clem model shows a minimum for the crystal (x=0.077) having the highest Tc(=35.05 K). This minimum value of λab(0) (=2545±40) is in agreement with the earlier reported value of λ(0) (∼2500) for a polycrystalline sample of (La1-xSrx)2CuO4 with x=0.075 obtained by using the muon-spin-relaxation technique.