Magnetic behavior of one-dimensional cobaltite SrxBa1-xCoO3 (x < 0.5)

PABLO M. BOTTA; VÍCTOR PARDO; DANIEL BALDOMIR; CRISTINA DE LA CALLE; JOSÉ A. ALONSO; JOSÉ RIVAS

Buenos Aires, Argentina

Congreso; At the Frontiers of Condensed Matter III (FCM III); 2006

The system BaCoO3 has recently received considerable attention because of their interesting magnetic properties. These are related to its uncommon crystalline structure, which consists in hexagonally ordered chains of CoO6 face-sharing octahedra, running along the c direction. The Co-Co distance along this axis is much shorter than between the chains, giving the structure a strong 1D character, while the triangular arrangement of these chains gives rise to the hexagonal structure. The isoelectronic substitution of Ba by Sr decreases the separation between the chains, changing the magnetic interactions. The hexagonal crystalline structure remains up to doping levels of 0.5.  Recent experiments on this system showed a competition between antiferromagnetic and ferromagnetic interactions. However, theoretical studies suggest the ground state is formed by ferromagnetic droplets of a nanometric size embedded in a non-ferromagnetic matrix, which is the signature of intrinsic nanoscale phase separation.  In this work, for further understanding the magnetism of SrxBa1-xCoO3, dc and ac magnetic susceptibilities at low applied fields as a function of temperature were measured. Powders with x ranging 0.1-0.5 were prepared by a citrate technique, using thermal treatments under high oxygen-pressure. dc susceptibility curves show a clear maximum, which appears at lower temperatures for higher applied fields. This behavior is typical for a fine-particle magnetic system with a blocking temperature, TB. ac susceptibility measurements confirm this magnetic response and also provide information about the thermal relaxation of the ferromagnetic clusters. The effect of doping with Sr on the phase separation phenomenon is discussed.