Interplay of 4f-3d Magnetism and Ferroelectricity in DyFeO3

DyFeO3 exhibits a weak ferromagnetism (TNFe ~ 645 K) that disappears below a spin-reorientation (Morin) transition at TSRFe ~ 50 K. It is also known that applied magnetic field induces ferroelectricity at the magnetic ordering temperature of Dy-ions (TNDy ~ 4.5 K). Here, we show that the ferroelectricity exists in the weak ferromagnetic state (TSRFe < T < TN,C) without applying magnetic field, indicating the crucial role of weak ferromagnetism in inducing ferroelectricity. 57Fe M\"ossbauer studies show that hyperfine field (Bhf) deviates from mean field-like behaviour that is observed in the weak ferromagnetic state and decreases below the onset of spin-reorientation transition (80 K), implying that the Bhf above TSR had additional contribution from Dy-ions due to induced magnetization by the weak ferromagnetic moment of Fe-sublattice and below TSR, this contribution decreases due to collinear ordering of Fe-sublattice. These results clearly demonstrate the presence of magnetic interactions between Dy(4f) and Fe(3d) and their correlation with ferroelectricity in the weak ferromagnetic state of DyFeO3.Comment: 5 pages, 6 figures, published in EP

Experimental observation of quantum corrections to electrical resistivity in nanocrystalline soft magnetic alloys

X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc &#945;-Fe/&#945; -FeSi crystallites with the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron-electron interaction (EEI) and quantum interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant, density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys in question

Oxalate based non-aqueous sol-gel synthesis of phase pure sub-micron LiFePO<SUB>4</SUB>

We report on the synthesis and preliminary characterisation by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer spectroscopy and infrared spectroscopy (IR) of C-LiFePO4. Homogeneous sub-micron sized particles of surface carbon coated phase pure LiFePO4 are synthesised by a novel non-aqueous oxalate based sol-gel procedure. Our synthetic route successfully overcomes the incidence of Fe3+, effectively controls undesirable particle growth and has the potential for upscaling and application as Li-ion battery cathodes

Direct conversion of calcium carbonate to C-1-C-3 hydrocarbons

With the objective of investigating the direct conversion of inorganic carbonates such as CaCO3 to hydrocarbons, assisted by transition metal ions, we have carried out studies on CaCO3 in an intimate admixture with iron oxides (FeCaCO) with a wide range of Fe/Ca mole ratios (x), prepared by co-precipitation. The hydrogen reduction of FeCaCO at 673 K gives up to 23% yield of the hydrocarbons CH4, C2H4, C2H6 and C3H8, leaving solid iron residues in the form of iron metal, oxides and carbide particles. The yield of hydrocarbons increases with x and the conversion of hydrocarbons occurs through the formation of CO. While the total yield of hydrocarbons obtained by us is comparable to that in the Fischer-Tropsch synthesis, the selectivity for C-2-C-3 hydrocarbons reported here is noteworthy

Investigation of structure and electrical transport in partially nanocrystallized amorphous soft magnetic alloys

X-ray diffraction patterns of melt-spun Fe-Cu-Nb-Si-B (FINEMET-type) alloys reveal that crystallites of Fe2Si and Fe3B phases with average sizes of 15(5) and 20(2) nm are present in the surface layer of thickness &#8776;10 &#197; and these nanocrystallites occupy 5-10% of the total volume. The results of an elaborate analysis of the high-resolution electrical resistivity data taken in a temperature range from 13 K to 300 K and their discussion in the light of existing theories demonstrates that the enhanced electron-electron interaction (EEI), quantum interference (QI) effects, inelastic electron-phonon scattering, coherent electron-magnon (and/or electron-spin fluctuation) scattering are the main mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon scattering is the most effective mechanism to destroy phase coherence of electron wavefunctions. The physical quantities such as diffusion constant, density of states at the Fermi level and the phase-breaking time, determined for the first time for the alloys in question, exhibit a systematic variation with the copper concentration

On the defect origin of the room-temperature magnetism universally exhibited by metal-oxide nanoparticles

The occurrence of ferromagnetism in nanoparticles of otherwise non-magnetic oxides seems to be well established. It is, however, necessary to understand the origin of ferromagnetism in these materials. Herein, we present a combined study of the magnetic properties and photoluminescence (PL) behavior of nanoparticles of ZnO, ZrO<SUB>2</SUB>, and MgO annealed at different temperatures (and therefore of different sizes). We find that the magnetization and the intensity of the bands due to defects vary parallel in all these materials. The adsorption of ethanol leads to a decrease in the magnetization and to a reduced intensity of the defect PL band of ZnO nanoparticles whereas UV irradiation has the opposite effect. We have also examined the effect of the morphology of the ZnO on the properties

Spin-reorientation, ferroelectricity and magnetodielectric effect in YFe_1−x Mn_xO₃ (0.1 &#8804; x &#8804; 0.40)

We report the observation of magnetoelectric and magnetodielectric effects at different temperatures in Mn-substituted yttrium orthoferrite, YFe_1−x Mn_xO₃ (0.1 &#8804; x &#8804; 0.40). Substitution of Mn in antiferromagnetic YFeO₃ (T_N = 640  K) induces a first-order spin-reorientation transition at a temperature, T_SR, which increases with x whereas the Neel temperature (T_N) decreases. While the magnetodielectric effect occurs at T_SR and T_N, the ferroelectricity appears rather at low temperatures. The origin of magnetodielectric effect is attributed to spin-phonon coupling as evidenced from the temperature dependence of Raman phonon modes. The large magnetocapacitance (18% at 50 kOe) near T_SR = 320  K and high ferroelectric transition temperature (&#8764;115  K) observed for x = 0.4 suggest routes to enhance magnetoelectric effect near room temperature for practical applications

Structure and complex magnetic behavior of disordered perovskite (Bi<SUB>0.5</SUB>Sr<SUB>0.5</SUB>)(Fe<SUB>0.5</SUB>Mn<SUB>0.5</SUB>)O<SUB>3</SUB>

Bi0.5Sr0.5)(Fe0.5Mn0.5)O3 crystallizes in a rhombohedral structure, with space group R3c, where the cations Bi3+/Sr2+ and Fe3+/Mn4+ occupy 6a and 6b sites respectively. Neutron diffraction, Mossbauer and magnetization measurements confirm long range antiferromagnetic ordering of the Fe3+ and Mn4+ moments at TN (226 K). Below TN, this oxide exhibits a cluster glass behavior and at low temperatures (~30 K) a spin glass state is observed. The complex magnetic behavior is attributed to cation disorder in the system. Magnetic properties of this oxide are compared with those of the isostructural Bi0.5La0.5Fe0.5Mn0.5O3 where both Fe and Mn ions exist in trivalent state