Crystal structure, magnetic and electrical properties of the Nd_1−<i>x</i>Ba_<i>x</i>CoO₃system

Abstract

The properties of Nd1?xBaxCoO3 (0?x?0.24) solid solutions were studied at non-ambient temperatures by x-ray and neutron powder diffraction methods as well as magnetization and resistivity measurements. All the samples have an orthorhombically distorted perovskite structure (Pbnm space group). It was found that compositions with x?0.06 exhibit paramagnetic behaviour down to liquid helium temperature, and those with 0.08?x?0.16 are spin glasses, whereas both long-range ferromagnetic order (?K) and metallicity above TC seem to occur simultaneously at x?0.18. According to neutron diffraction data at different temperatures (T = 3?540?K), there are no crystal structure anomalies associated with orbital ordering of the Co3+ ions in the intermediate-spin state for NdCoO3. This is in agreement with gradual thermal excitation of the Co3+ ions from low-?to intermediate-?or high-spin state in a wide temperature range up to a metal?insulator transition (~600?K). The possible mechanisms of magnetic interactions are discussed.