Infrared and magnetic characterization of the multiferroic Bi2FeCrO6 thin films in a broad temperature range

Infrared reflectance spectra of an epitaxial Bi2FeCrO6 thin film prepared by pulsed laser deposition on LaAlO3 substrate were recorded between 10 and 900 K. No evidence for a phase transition to the paraelectric phase was observed, but some phonon anomalies were revealed near 600 K. Most of the polar modes exhibit only a gradual softening, which results in a continuous increase of the static permittivity on heating. It indicates that the ferroelectric phase transition should occur somewhere above 900 K. Magnetic measurements performed up to 1000 K, revealed a possible magnetic phase transition between 600 and 800 K, but the exact critical temperature cannot be determined due to a strong diamagnetic signal from the substrate. Nevertheless, our experimental data show that the B-site ordered Bi2FeCrO6 is one of the rare high-temperature multiferroics.Comment: subm. to PR

Hydrothermal synthesis, characterization, and magnetic properties of cobalt chromite nanoparticle

The CoCr2O4 nanoparticles were prepared by hydrothermal treatment of chromium and cobalt oleates in a mixture of solvents (water and ethanol or pentanol) at various temperatures. The samples were further annealed at the temperatures from 300 to 500 C. The obtained nanoparticles were characterized using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy, and magnetic measurements. The particle size, ranging from 4.4 to 11.5 nm, was determined from the TEM and PXRD methods. The tendency of particles to form the aggregates with the increasing annealing temperature has been observed. The magnetic measurements revealed that the typical features of the CoCr 2O4 long-range magnetic order are suppressed in the nanoparticles

Critical size limits for collinear and spin-spiral magnetism in CoCr_2\mathrmO_4

The multiferroic behavior of CoCr2O4 results from the appearance of conical spin-spiral magnetic ordering, which induces electric polarization. The magnetic ground state has a complex size-dependent behavior, which collapses when reaching a critical particle size. Here the magnetic phase stability of CoCr2O4 in the size range of 3.6–14.0 nm is presented in detail using the combination of neutron diffraction with XYZ polarization analysis and macroscopic magnetization measurements. We establish critical coherent domain sizes for the formation of the spin spiral and ferrimagnetic structure and reveal the evolution of the incommensurate spin spiral vector with particle size. We further confirm the presence of ferroelectric polarization in the spin spiral phase for nanocrystalline CoCr2O4

Materiali nanofasici

This booklet collects the abstracts of the scientific contributions presented at the XI Convegno Nazionale Materiali Nanofasici held in Rome on October 26-28, 2015. The objective of the Conference was to bring together the whole Italian Nanoscience Community (physicists, chemists and engineers) providing a forum for discussion on the recent developments in the understanding of the fundamental chemical and physical properties of nanophase materials and their technological applications

Materiali nanofasici

This booklet collects the abstracts of the scientific contributions presented at the XI Convegno Nazionale Materiali Nanofasici held in Rome on October 26-28, 2015. The objective of the Conference was to bring together the whole Italian Nanoscience Community (physicists, chemists and engineers) providing a forum for discussion on the recent developments in the understanding of the fundamental chemical and physical properties of nanophase materials and their technological applications