Tunable multiferroic order parameters in Sr1- x Ba x Mn1- y Ti y O3.

Responding to the rapidly increasing demand for efficient energy usage and increased speed and functionality of electronic and spintronic devices, multiferroic oxides have recently emerged as key materials capable of tackling this multifaceted challenge. In this paper, we describe the development of single-site manganese-based multiferroic perovskite materials with modest amounts of nonmagnetic Ti substituted at the magnetic Mn site in Sr1- x Ba x Mn1- y Ti y O3 (SBMTO). Significantly enhanced properties were achieved with ferroelectric-type structural transition temperatures boosted to ∼430K. Ferroelectric distortions with large spontaneous polarization values of ∼30µC/cm2, derived from a point charge model, are similar in magnitude to those of the prototypical nonmagnetic BaTiO3. Temperature dependence of the system's properties was investigated by synchrotron x-ray powder diffraction and neutron powder diffraction at ambient and high pressures. Various relationships were determined between the structural and magnetic properties, Ba and Ti contents, and T N and T C. Most importantly, our results demonstrate the large coupling between the magnetic and ferroelectric order parameters and the wide tunability of this coupling by slight variations of the material's stoichiometry.

Spectroscopic and quantum chemical studies of interaction between the alginic acid and Fe3O4 nanoparticles.

In this work, we present the spectral investigation of the interactions between the coverage with alginic acid (AA) and nanoparticles for three different composites containing 74, 80, and 88wt% of magnetite. These results show that the Fe3O4 nanoparticles are coated with the AA and indicate that there is an interaction between them. Moreover, we have investigated the thermal and magnetic properties of all investigated compounds. We show that bonding of alginic acid to the surface of magnetite results in better thermal stability of the polymer and in higher temperature of AA chains degradation. We find that for dense assembly of magnetite nanoparticles, at low temperatures, the intergranular coupling becomes much stronger than between nanoparticles dispersed in composites.

Dielectric response and specific heat studies of Cd2Nb2O7 ceramics obtained from mechano-synthesized nanopowders.

Cd(2)Nb(2)O(7) is still an interesting ferroelectric material because of its high permittivity value at helium temperatures and a variety of dielectric relaxation processes, the origin of which is still puzzling. We prepared hot-pressed ceramics, with grain sizes from 100 to 150 nm, obtained from Cd(2)Nb(2)O(7) nanopowders synthesized by high-energy milling of CdO and Nb(2)O(5) and studied their dielectric response and thermal properties. The nanoceramics were characterized by X-ray diffraction and their dielectric properties were measured at temperatures from 4K to 575K. Dielectric response of the nanoceramics was found to consist of a huge anomaly at ~150K with complex dielectric absorption and three relaxation processes apparent in frequency and temperature dependences of the imaginary part of permittivity in the temperature range from 18K to 145K. The anomaly at ~150K is related to overlapping contributions from the Curie point (shifted downward because of the size effect) and a dielectric relaxation process. The behavior of three relaxation modes observed at temperatures below 145K is discussed, based on the model proposed by Malcherek of polar nanoregions in the orthorhombic phase of Cd(2)Nb(2)O(7) and the theory of dielectric response of ferroelectric relaxors by Bokov and Ye.