Superconductivity and magnetism of Sm1.85-xGdxCe0.15CuO4-delta and Gd2-yCeyCuO4-delta crystals

The magnetism and superconductivity of Sm 1 . 8 5 - x Gd x Ce 0 . 1 5 CuO 4 - Φ and Gd 2 - y Ce y CuO 4 - Φ crystals were investigated. In the Sm 1 . 8 5 - x Gd x Ce 0 . 1 5 CuO 4 - Φ system, superconductivity is suppressed by Gd substitution, and temperature-induced magnetic transitions appear at 3, 7, and 135 K above x = 1.2 Cu spins have an antiferromagnetic (AF) order along the [110] direction among these transitions, and a weak-ferromagnetic (WF) moment due to a canting of Cu spins appears along the [110] direction at T≤3 K and 7 K≤T≤135 K. The AF order at 3 K≤T≤ 7 K changes into a canted spin configuration via field-induced spin reorientation and induces the WF moment. The Neel temperature T N C u (135 K at x= 1.2) and spin-reorientation temperature T S R (7 K at x = 1.2), which are due to the Cu sublattice and are observed at low field intensity, increase with increasing x. Sm spins have an antiferromagnetic order along the [001] direction at x = 0 below the Neel temperature T N R (∼5 K), but T N R , which is observed for low x at high field intensity, decreases with increasing x and disappears at x1. Gd spins have an antiferromagnetic order along the [110] direction for specimens with x>1.4 near 3 K. The change in the geometry of rare-earth and Cu spins resulting from Gd substitution is considered to he the reason for the suppression of superconductivity.