IrSr 2TbCu 2O 8, a high-pressure metamagnetic cuprate: Structure, microstructure and properties

Abstract

The synthesis, structure and microstructure of the IrSr 2TbCu 2O 8 cuprate showing metamagnetic properties are described. The sample was prepared at high temperatures and pressures up to 9.2 GPa. The structure is tetragonal, showing a 1212 type structure, that derives from the classical YBaCuO superconductor structure, replacing the tetracoordinated square planar copper [Cu–O 4] in the “chains” by octahedral [Ir–O 6] groups that form a perovskite-like layer in the basal plane of the unit cell. A “simple” cell, ∼ a p× a p×3 a p, where a p is the basic perovskite unit cell parameter ( a p∼3.8 Å), is supported by X-ray powder diffraction (XRD) and a so-called “diagonal” one, ∼√2 a p×√2 a p×3 a p, by SAED; a microdomain texture of latter cell and a series of very interesting extended defects have been observed by HREM. Magnetic susceptibility measurements show a magnetic transition, T N∼6 K, with negative Weiss temperature, that indicates antiferromagnetic interactions among the Tb moments. The magnetic structure has been determined by neutron diffraction. A detailed magnetic study has revealed a metamagnetic behavior, something not previously observed in this type of cuprates. Specific heat and resistivity measurements have also been performed to characterize the transition.