Compositional dependence of transport anisotropy in large (La, Sr)2CuO4 single crystals and second peak in magnetization curves

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Abstract

Large single crystals of (La1 − xSrx)2CuO4, up to 5 mm along the crystal c-axis, have been grown over a composition range of x = 0.03 to 0.15, covering the whole superconducting region in this system. A complete set of electrical resistivity data along both the c-axis (ϱc) and ab-plane (ϱab) have been obtained via the DC four-probe method for the first time. As x was varied, both resistivities changed monotonically from semiconductive to metallic in character and the critical temperature, Tc defined by the mid point of the resistive transition curves, passed through a maximum value of 38.8 K at x= 0.072. The anisotropy ratio ϱr/g9ab at 50 K decreased drastically with increasing x, from nearly 4000 to 160, while it was appoximately 350 at x = 0.072> Magnetization hysteresis curves (H||c, ± 9 T) revealed the presence of an additional pinning mechanism in the over-doped region (x ⩾ 0.072) giving rise to a second peak at moderately high fields. This was attributed to enhanced flux pinning by oxygen vacancies nominally present in this composition range.

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