Characteristic crossing point (T_*≈2.7 K) in specific heat curves of samples RuSr₂Gd_1.5Ce_0.5Cu₂O_10−δtaken 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-δ), as-prepared (by solid-state reaction) and annealed (12 h at 845 °C) in pure oxygen at different pressure (30, 62 and 78 atm) are presented. The specific heat and magnetization were investigated in the temperature range 1.8-300 K with a magnetic field up to 8 T. The specific heat, C(T), shows a jump at the superconducting transition (with an onset at T≈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(*)≈2.7 K) for all the samples studied. At the same time, C(H) curves taken for different temperatures have a crossing point at a characteristic field H(*)≈3.7 T. These effects can be considered as a manifestation of the crossing point phenomenon which is supposed to be inherent for strongly correlated electron systems.

Hysteresis and stepwise structure in MR curves of granular superconducting ruthenocuprates RuSr2(Gd1.5Ce0.5)Cu2O10−δ

“…4 for the Gd ruthenocuprates), which agree with known data [6]. Below T c the Ru1222 compounds show a ferromagneticlike behavior together with diamagnetic (Meissner) response at low applied fields [6,11,22]. At higher fields no saturation takes place due to paramagnetic contribution from rare-earth ions or impurity phases (Fig.…”

“…Most important results concerning this and similar Ru1222 samples are already presented in previous papers [11,22]. Here we would like to show only typical magnetization hysteresis curve in the temperature range of superconducting state (see Fig.…”

“…It was shown previously [11,22] that oxygen annealing of these samples has a rather strong effect on intergrain connection but does not influence intragrain superconducting properties. This study focuses on properties of as-prepared Ru1222-Gd samples where the granularity effects were most evident.…”

“…The samples were polycrystalline with a grain size of a few µm. They were characterized by resistivity, magnetization and specific heat measurements, which were in part reported in [11,22].…”

“…The temperature T c0 = 34 K (shown by arrow) marks a kink in the R(T ) dependences and is attributed to the intragrain superconducting transition. This value of T c0 is determined on the basis of transport, magnetic and heat capacity measurements [11,22]. Weak intergrain connection causes nonmetallic behavior of R(T ) above T c0 (dR/dT < 0) with an approximately logarithmic law (∆R ∝ ln T ).…”