Interplay of structural and magnetic nanoscale phase separation in layered cobaltites

摘要

We report on the structural, electronic, and magnetic phases of a previously unexplored region in the phase diagram of GdBaCo_2O_(5+δ) (δ = 0.57 and 0.63). Despite a homogenous average structure displayed by both the samples, the orthorhombic highly oxygenated GdBaCo_2O_(5.63) shows clear signatures of structural nanoscale phase separation. By combining a pair distribution function with photoluminescence and electron spin resonance techniques, we found that the nanoscale phase separation is induced by an inhomogeneous distribution of ferromagnetic Co~(3+) - Co~(4+) clusters embedded in an antiferromagnetic Co~(3+)-rich matrix. In addition, we uncovered a phase evolution involving the collapse of the orthorhombic strain below room temperature. The origin of this noncanonical transition seems to be associated with the interplay of the observed nanoscale phase separation and a new magnetic phase transition occurring below T ～ 180 K.