Magnetic and superconducting properties of single-crystal TmNi2B2C

Abstract

The temperature (T) and applied magnetic field (H) dependent magnetization has been measured for a single crystal of TmNi2B2C in order to study the interplay of superconductivity and the magnetism of the Tm sublattice. The normal-state magnetization of TmNi2B2C is anisotropic from 2 to 300 K with the magnetic field applied normal to the c axis (H⊥c) leading to a smaller induced magnetization than the magnetization for the magnetic field applied parallel to the c axis (H∥c). This anisotropy is attributed to crystalline electric field (CEF) splitting of the J=6 manifold of the Tm+3 ion. From the inverse susceptibility [1/χ(T)] for H∥c and H⊥c, the CEF parameter, B20, is found to be (-1.15±0.02) K. The superconducting state magnetization for H≊Hc2(T) obeys the Ginzburg-Landau theory which is used to evaluate the upper critical magnetic field Hc2(T) and dHc2/dT‖Tc values. The superconducting properties in this temperature region are similar to those of the nonmagnetic superconductor YNi2B2C, which has been shown to be an isotropic conventional type-II superconductor. For T≤6 K, Hc2(T) shows highly anisotropic behavior: Hc2⊥c≊2Hc2∥c. For both H∥c and H⊥c, Hc2(T) reaches a broad maximum near 4 K and decreases as T approaches TN=(1.52±0.05) K, indicating the interplay between superconductivity and magnetism. The broad maximum in Hc2(T) of TmNi2B2C is likely a result of the increasing Tm sublattice magnetization at Hc2(T) with decreasing temperature, rather than of antiferromagnetic fluctuations.

Source-reported materials — not catalogue approval

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