Superconductivity and magnetism ofSm1.85−xGdxCe0.15CuO4−δandGd2−yCeyCuO4−δcrystals

Abstract

The magnetism and superconductivity of ${\mathrm{Sm}}_{1.85\ensuremath{-}x}{\mathrm{Gd}}_{x}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{Gd}}_{2\ensuremath{-}y}{\mathrm{Ce}}_{y}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ crystals were investigated. In the ${\mathrm{Sm}}_{1.85\ensuremath{-}x}{\mathrm{Gd}}_{x}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$ 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 $[1\ifmmode\bar\else\textasciimacron\fi{}10]$ direction at $Tl~3\mathrm{K}$ and $7\mathrm{K}l~Tl~135\mathrm{K}.$ The AF order at $3\mathrm{K}l~Tl~7\mathrm{K}$ changes into a canted spin configuration via field-induced spin reorientation and induces the WF moment. The N\'eel temperature ${T}_{\mathrm{NCu}}$ (135 K at $x=1.2)$ and spin-reorientation temperature ${T}_{\mathrm{SR}}$ (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 N\'eel temperature ${T}_{\mathrm{NR}}$ (\ensuremath{\sim}5 K), but ${T}_{\mathrm{NR}},$ which is observed for low x at high field intensity, decreases with increasing x and disappears at $x\ensuremath{\approx}1.$ Gd spins have an antiferromagnetic order along the $[1\ifmmode\bar\else\textasciimacron\fi{}10]$ direction for specimens with $xg1.4$ near 3 K. The change in the geometry of rare-earth and Cu spins resulting from Gd substitution is considered to be the reason for the suppression of superconductivity.