Ferromagnetic clusters in polycrystalline BaCoO3

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

San Sebastián, España

Simposio; Joint European Magnetic Symposium (JEMS 06); 2006

BaCoO3 is a mixed oxide that 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 octahedra. Recent results based on theoretical and experimental analyses suggest that the magnetic properties of the system can be explained assuming the material is formed by ferromagnetic regions of a nanometric size embedded in a nonferromagnetic matrix. For further exploring the properties of BaCoO3, we have measured the magnetic susceptibility at very low fields both in DC and AC conditions. The compound was prepared in powder form by a citrate technique, using thermal treatments under high oxygen-pressure. Rietveld analysis of the obtained product reveals a crystalline structure corresponding to the hexagonal space group P63/mmc. DC susceptibility (measured under ZFC conditions) as a function of temperature shows a clear maximum, which appears at lower temperatures for higher applied fields. This behaviour 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.  A good fit to an Arrhenius-like behaviour together with an average size of about 1 nm are found for these clusters.