Negative Magnetization and Superconductivity in the (LaPt2Asx (x=1, 2) and BaPt2As2 Compounds

Abstract

We have investigated the electrical and magnetic properties of the compounds LaPt2As, LaPt2As2, and BaPt2As2 prepared by conventional solid-state reaction, in the temperature range of 5-300 K, up to the field of H = 9 T. The zero-field cooled magnetization (M-ZFC) and field cooled magnetization (M-FC) split into two branches at the bifurcation temperatures due to large thermal hysteresis effects. A huge diamagnetic magnetization has been manifested on the M-ZFC branches in both samples. We describe different possible scenarios of the negative magnetization-like behavior. First, this huge diamagnetic signal may arise from some local nano-sized ferromagnetic clusters subjected to the negative internal field, which is originated from the local distortions in the electronic structure due to the inhomogeneous Pt atoms distributions. The second is suggested as an alternative model, so that the present phenomenon was not a true negative magnetization, the observed negative magnetization, in fact, is relative change in the magnetization. It may arise from the freezing spins at lower temperatures. The magnetic analysis reveals the development of superconductivity with a filamentary character at temperatures below 10 K for the sample LaPt2As and 22 K for the sample LaPt2As2. In order to prove the observed superconductivity, their critical current density, J(c)(H), and the normalized pinning force, F-p/(Fp,max), are obtained as a function of the applied field, and the types of flux pinning centers are identified using the conventional Beans and Dew-Hughes models. We report the resistivity data in the same temperature interval. The resistivity curves are fitted to the form rho(T) = rho(0) + rho T-1(alpha) + rho(2)exp (- T-o/T) over the entire range of the measurement temperatures. The last term presents a magnon-assisted inter-band electron-phonon electron scattering mechanism. In addition, we observe an anomaly around 115 K in LaPt2As2 associated with the charge density (CDW) phase transition.