Superconductivity and magnetism in a novel La0.85Ga0.15FeAsO compound

We report magnetization measurements on samples of La 0.85 Ga 0.15 FeAsO in the wide temperature range of 10 K-400 K, up to the field of 90 kOe having been prepared by solid-state reaction. This novel compound crystallizes with the tetragonal ZrCuSiAs-type structure. The crystal structure was determined by X-ray powder diffraction (P4/nmm: a =4.032Å, and c=8.741 Å). Temperature dependence of magnetization for this compound is measured with zero-field cooling (ZFC) and field cooling (FC) with an application of H = 50 Oe. The large bifurcation between the ZFC and FC curves has been observed starting at around 370 K. At lower temperatures below T s c s e t − o n ∼ 37 K, superconductivity and magnetism coexist. Intermediate temperature range (37 K< T < 300 K), the sample is in a mixed state of the ferromagnetic clusters with paramagnetic moments, described well by the Modified Curie Weiss expression. At higher temperatures above 360 K, it is a pure paramagnetic, described perfectly by the simple Curie-Weiss expression. The natures of the superconducting flux-pinning centers are revealed based on analysis of the pinning force, F pin at T = 10 K. The normalized pinning force, F p /F p, max versus H indicates the filamentary character owing to the pinning parameters, p =0.5, q =2. These results point out that, in the superconductivity, the dominance of grain boundary with single-vortex pinning (μ =1/7) mechanism The Curie temperature, T curie was estimated using the modified Arrot plots. The critical exponents, β, ϒ, and δ were estimated, their values are in close agreement with those predicted for a mean-field-like behavior at a magnetic phase transition.