Magnetism and superconductivity in single-crystal ErNi2B2C

Abstract

The resistivity ρab(T) and anisotropic magnetization M(T) of ErNi2B2C crystals were measured as a function of applied magnetic field (H) from 2 to 300 K to study the magnetic and superconducting properties with H parallel and perpendicular to the c axis (H∥c and H⊥c). Low-temperature specific-heat measurements for H=0 show a lambda-shaped anomaly associated with antiferromagnetic (AF) ordering at TN=(5.85±0.15) K. The ρab(T) and M(T) data show a superconducting transition at Tc=10.5 K, long-range AF ordering at TN=6.0 K, and coexistence of superconductivity and antiferromagnetism below TN. From the ρab(T) and M(T) data, the TN was found to be independent of H up to H=20 kG for H∥c, whereas for H⊥c TN decreased as ∼H2 from 6.0 K at H=0 to TN=3.2 K at H=18 kG. The M(T) data show a change in the easy axis direction from H∥c above 150 to H⊥c below 150 K. This change in anisotropy is associated with the anomalously small magnitude of the crystalline electric field B20 term. The superconducting upper critical magnetic fields Hc2(T) for H∥c and H⊥c, determined from M(T) and ρab(H,T) data, show anomalies for both field orientations near TN. However, the local minimum of Hc2(T) near TN, seen previously for both H⊥c and H∥c in a HoNi2B2C crystal, was found only for H∥c in ErNi2B2C. This anisotropy in Hc2(T) is likely a result of the anisotropy of the Er sublattice magnetization, specifically the anisotropy of TN(H). The depth of the local minimum in Hc2 for H∥c for ErNi2B2C near TN is comparable to the one for HoNi2B2C at 5 K.

Source-reported materials — not catalogue approval

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