Heat-capacity and magnetic measurements on the Y(Ni2−xCo

Abstract

We have performed field-and temperature-dependent magnetization, resistivity, and heat-capacity measurements on polycrystalline samples of the Y͑Ni 2Ϫx Co x )B 2 C system with 0.0рxр0.4. Values of T c , 0 ,H c2 ,⌰ D , , and N(E d ) were determined for various samples. We observe that ⌰ D increases with x, while all the other parameters decrease with x. The T c vs x data can be described using the BCS theory and the measured values of N(E f ) and ⌰ D . The results suggest that the decrease in T c is due to the decrease in N(E f ), in agreement with the results from band structure calculations.

The classification of superconductors using muon spin rotation

“…For example, band structure calculations suggest an essentially isotropic 3d electronic structure and associate the relatively high transition temperatures with a van Hove-like peak in the density of states at the Fermi energy [16]. Experimental evidence for this peak has been provided by studies of the effect of partial 3d transition metal substitution for Ni in YNi2B2C [17,18]. Within the rigid band model such substitution is viewed as shifting the Fermi energy away from the peak of the density of states, thereby reducing T c. Nevertheless controversy persists: antiferromagnetic spin fluctuations have been invoked to explain the unusual temperature dependence of the llB spin lattice relaxation and Knight shift in YNi2B2C and LuNi2B2C [19,20], and, more recently, the presence of superconductivity itself in LuNi2B2C [ 11 ].…”

“…Within the Uemura classification scheme YB6, like Y N i z B 2 C , therefore lies extremely close to the boundary separating exotic from conventional supereonducting systems. This perhaps provides the first indication that superconduetivity in YB 6 may not be entirely conventional.Heat capacity measurements on the Y(Ni l_xCox)2B2C system have provided Sommerfeld constants of 15.2 and 12 mJ mol -1K -2 for compounds with x = 0.05 and x = 0.10, respectively[18]. Combining these values with the measured penetraThe results of the IxSR experimems on YB6, YNi2B2C (from[21]), Y(Nio.95Co0.os)2B2C and Y(Nio.90Co0a0)2B2C summarized on the Uemura plot of T c vs T r. The proximity of all four compounds to the so-called "exotic" superconduetors is evident.…”

Study of the superconducting gap inRNi2B2C(R=Yang1, Klein2, Cooper3 et al. 2000Phys. Rev. B514330View full textAdd to dashboardCite

“…The rare-earth borocarbides are believed to be conventional BCS-type superconductors 1 with a number of interesting properties that are not fully understood. Borocarbides are similar to intermetallic superconductors such as V 3 Si and Nb 3 Sn in that they have a relatively strong electron-phonon coupling constant and a moderately large density of states at the Fermi level.…”

Islands of (In-)stability in High Temperature Superconductors

“…11 These two facts might help to clarify why we see the temperature limit in YBCO and no such limit in the case of YNi 2 B 2 C. Here the heat capacity varies in the examined temperature range only between ≈0.1 and 1.2 J/(mol K). 12 This relatively small heat capacity change might not be sufficient to suppress dendrite development. However, we do not observe the raise in the field where the first instability is expected (Eq.…”