Competing magnetic interactions and low temperature magnetic phase transitions in composite multiferroics

Novel magnetic properties and magnetic interactions in composite multiferroic oxides Pb [(Zr0.52Ti0.48)(0.60)(Fe0.67W0.33)(.40)]O-3](0.80)-[CoFe2O4](0.20) (PZTFW-CFO) have been studied from 50 to 1000 Oe field cooled (FC) and zero field cooled (ZFC) probing conditions, and over a wide range of temperatures (4-350 K). Crystal structure analysis, surface morphology, and high resolution transmission electron microscopy images revealed the presence of two distinct phases, where microand nano-size spinelCFO were embedded in tetragonal PZTFW matrix and applied a significant built-in compressive strain (similar to 0.4-0.8%). Three distinct magnetic phase transitions were observed with the subtle effect of CFO magnetic phase onPZTFW magnetic phase transitions below the blocking temperature (T-B). Temperature dependence magnetic propertym(T) shows a clear evidence of spin freezing in magnetic order with lowering in thermal vibration. Chemical inhomogeneity and confinement of nanoscale ferrimagnetic phase in paramagnetic/antiferromagnetic matrix restrict the long range interaction of spin which in turn develop a giant spin frustration. A large divergence in the FC and ZFC data and broad hump in ZFC data near 200 (+/- 10) Kwere observed which suggests that large magnetic anisotropy and short range order magnetic dipoles lead to the development of superparamagnetic states in composite.