IrSr2TbCu2O8, a high-pressure metamagnetic cuprate: Structure, microstructure and properties

The synthesis, structure and microstructure of the IrSr2TbCu2O8 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–O4] in the “chains” by octahedral [Ir–O6] groups that form a perovskite-like layer in the basal plane of the unit cell. A “simple” cell, ∼ap×ap×3ap, where ap is the basic perovskite unit cell parameter (ap∼3.8 Å), is supported by X-ray powder diffraction (XRD) and a so-called “diagonal” one, ∼√2ap×√2ap×3ap, 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, TN∼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.