IrSr2Sm1.15Ce0.85Cu2.175O10: A reentrant spin-glass material

A new iridium-containing layered cuprate material, Ir0.825Sr2Sm1.15Ce0.85Cu2.175O10, has been synthesized by conventional ambient-pressure solid-state techniques. The material's structure has been fully characterized by Rietveld refinement of high-resolution synchrotron x-ray diffraction data; tilts and rotations of the IrO6 octahedra are observed as a result of a bond mismatch between in-plane Ir-O and Cu-O bond lengths. DC-susceptibility measurements evidence a complex set of magnetic transitions upon cooling that are characteristic of a reentrant spin-glass ground-state. The glassy character of the lowest-temperature (T-g = 10 K) transition is further confirmed by AC-susceptibility measurements, showing a characteristic frequency dependence that can be well fitted by the Vogel-Fulcher law and yields a value of Delta T-f/[T-f Delta log(omega)] = 0.015(1), typical of dilute magnetic systems. Electronic transport measurements show the material to be semiconducting at all temperatures, so that the CuO2 planes are underdoped with no evidence of a transition to a superconducting state. Negative magnetoresistance is observed when the material is cooled below 20 K, and the magnitude of this magnetoresistance is seen to increase upon cooling to a value of MR = -9% at 8 K.