Magnetism, specific heat, and pressure-dependent resistivity of the electron-doped compounds Ln 2−x M x CuO 4−y (Ln = Pr, Nd, Sm, Eu, Gd; M = Ce, Th)

Abstract

Abstract Measurements of the magnetic susceptibility z the specific heat C, and the electrical resistivity ρ are presented for the Nd 2 CuO 4 -type structure insulating parent compounds Ln 2 CuO 4 (Ln = Pr, Nd, Sm, Eu, and Gd), the doped superconducting compounds Ln 2−x M x CuO 4−y (Ln = Pr, Nd, Sm, and Eu, M = Ce; Ln = Pr and Nd, M = Th), and the doped, semiconducting compound Gd 2−x Ce x CuO 4−y . The z and C data indicate that antiferromagnetic (AFM) order occurs in the undop compounds for Ln = Nd, Sm, and Gd at temperatures below 1.7 K, 5.95 K, and 6.6 K, respectively. The coexistence of superconductivity and AFM order is observed in Ln 1.85 M 0.15 CuO 4−y , with reduced Neel temperatures T N = 1.2 K for Ln = Nd, M = Ce, Th and T N = 4.6 K for Ln = Sm, M = Ce. Magnetic susceptibility data for Gd 2−x Ce x CuO 4−y display evidence for AFM ordering of Cu 2+ spins at ≈ 280 K for x = 0 and at ≈ 150 K for x = 0.15. For Nd 1.85 M 0.15 CuO 4−y , a very slight increase (decrease) in T c with applied pressure is observed for M = Ce (Th); this relative insensitivity and the depression of T c for M = Th is in contrast to the behavior observed for other high T c compounds.