Characteristic crossing point ($T_{\ast }\approx 2.7$ K) in specific-heat curves of samples RuSr${}_2$Gd${}_{1.5}$Ce${}_{0.5}$Cu${}_2$O${}_{10-\delta }$ taken for different values of magnetic field

Abstract

Magnetic properties of polycrystalline samples of RuSr${}_2$(Gd${}_{1.5}$Ce${}_{0.5}$)Cu${}_2$O${}_{10-\delta }$, as-prepared (by solid-state reaction) and annealed (12 hours at 845${}^{\circ }$C) in pure oxygen at different pressure (30, 62 and 78 atm) are presented. Specific heat and magnetization were investigated in the temperature range 1.8--300 K with a magnetic field up to 8 T. Specific heat, $C(T)$, shows a jump at the superconducting transition (with onset at $T\approx 37.5$ K). Below 20 K, a Schottky-type anomaly becomes apparent in $C(T)$. This low-temperature anomaly can be attributed to splitting of the ground term ${}^8{S}_{7/2}$ of paramagnetic Gd${}^{3+}$ ions by internal and external magnetic fields. It is found that curves $C(T)$ taken for different values of magnetic field have the same crossing point (at $T_{\ast }\approx 2.7$ K) for all samples studied. At the same time, $C(H)$ curves taken for different temperatures have a crossing point at a characteristic field $H_{\ast }\approx 3.7$ T. These effects can be considered as manifestation of the crossing-point phenomenon which is supposed to be inherent for strongly correlated electron systems.

10 pages, 7 figures, submitted to J. Phys.: Condens. Matter