Ferromagnetism in Multiferroic BaTiO₃, Spinel MFe₂O₄ (M = Mn, Co, Ni, Zn) Ferrite and DMS ZnO Nanostructures

Multiferroic magnetoelectric material has significance for new design nano-scale spintronic devices. In single-phase multiferroic BaTiO3, the magnetism occurs with doping of transition metals, TM ions, which has partially filled d-orbitals. Interestingly, the magnetic ordering is strongly related with oxygen vacancies, and thus, it is thought to be a source of ferromagnetism of TM:BaTiO3. The nanostructural MFe2O4 (M = Mn, Co, Ni, Cu, Zn, etc.) ferrite has an inverse spinel structure, for which M2+ ions in octahedral site and Fe3+ ions are equally distributed between tetrahedral and octahedral sites. These antiparallel sub-lattices (cations M2+ and Fe3+ occupy either tetrahedral or octahedral sites) are coupled with O2- ion due to superexchange interaction to form ferrimagnetic structure. Moreover, the future spintronic technologies using diluted magnetic semiconductors, DMS materials might have realized ferromagnetic origin. A simultaneous doping from TM and rare earth ions in ZnO nanoparticles could increase the antiferromagnetic ordering to achieve high-Tc ferromagnetism. The role of the oxygen vacancies as the dominant defects in doped ZnO that must involve bound magnetic polarons as the origin of ferromagnetism

Ferroelectricity of Neel-type magnetic domain walls

The chirality-dependent magnetoelectric properties of Neel-type domain walls in iron garnet films is observed. The electrically driven magnetic domain wall motion changes the direction to the opposite with the reversal of electric polarity of the probe and with the chirality switching of the domain wall from clockwise to counterclockwise. This proves that the origin of the electric field induced micromagnetic structure transformation is inhomogeneous magnetoelectric interaction.Comment: 6 pages, 4 figures, 1 tabl

Rapid green synthesis of ZnO nanoparticles using a hydroelectric cell without an electrolyte

In this study, zinc oxide (ZnO) nanoparticles were synthesized using a novel environmentally friendly hydroelectric cell without an electrolyte or external current source. The hydroelectric cell comprised a nanoporous Li substituted magnesium ferrite pellet in contact with two electrodes, with zinc as the anode and silver as an inert cathode. The surface unsaturated cations and oxygen vacancies in the nanoporous ferrite dissociated water molecules into hydronium and hydroxide ions when the hydroelectric cell was dipped into deionized water. Hydroxide ions migrated toward the zinc electrode to form zinc hydroxide and the hydronium ions were evolved as H-2 gas at the silver electrode. The zinc hydroxide collected as anode mud was converted into ZnO nanoparticles by heating at 250 degrees C. Structural analysis using Raman spectroscopy indicated the good crystallinity of the ZnO nanoparticles according to the presence of a high intensity E-2-(high) mode. The nanoparticle size distribution was 5-20 nm according to high resolution transmission electron microscopy. An indirect band gap of 2.75 eV was determined based on the Tauc plot, which indicated the existence of an interstitial cation level in ZnO. Near band edge and blue emissions were detected in photoluminescence spectral studies. The blue emissions obtained from the ZnO nanoparticles could potentially have applications in blue lasers and LEDs. The ZnO nanoparticles synthesized using this method had a high dielectric constant value of 5 at a frequency of 1 MHz, which could be useful for fabricating nano-oscillators. This facile, clean, and cost-effective method obtained a significant yield of 0.017 g for ZnO nanoparticles without applying an external current source

Green hydroelectrical energy source based on water dissociation by nanoporous ferrite

Dissociation of water molecule occurs on octahedrally coordinated unsaturated suface cations and oxygen vacancies created by lithium substitution in magnesium ferrite. Lower synthesis temperature of ferrite has generated nanopores in microstructure. Dissociated hydronium and hydroxyl ions are transported through surface and capillary diffusion in porous ferrite network towards attached Zn and Ag electrodes. Water molecule dissociation ability of nanoporous ferrite has been exploited to develop a green electrical energy cell, which is a combination of material science and electrode chemistry. The innovated cell has been nomenclatured as hydroelectric cell (HEC). When HEC is partially dipped in deionized water, spontaneously hydroxide and hydronium ions are produced by water molecule dissociation. Hydronium ions trapped in nanopores develop enough electric field that further dissociates physisorbed water molecules. Thereby, the process of water molecule dissociation is accelerated in a bigger way to increase ionic current in the cell. Oxidation of Zn electrode by hydroxide ion and reduction of H3O+ at Ag electrode develop voltage and electric current in the cell. The HEC cell of a 17 cm(2) area is able to generate a short circuit current of 82mA and 920 mV emf with a maximum output power of 74 mW, which is three order higher than reported output power 1.4 mu W/cm(2) produced by water in cement matrix. Hydroelectric cell performance is repetitive, stable and possesses potential to replace traditional ways of generating renewable energy in terms of cost and safety

Bimodal Co0.5Zn0.5Fe2O4/PANI nanocomposites: Synthesis, formation mechanism and magnetic properties.

Co0.5Zn0.5Fe2O4/PANI nanocomposites with bimodal size distribution were synthesized via reverse microemulsion method. Structural characterization was done by Fourier transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Vibrating sample magnetometer measurement confirmed the ferromagnetic behavior of nanocomposite with saturation magnetization of 3.95 emu/g and low coercive force (39 Oe). It was observed that on nanocomposite formation with PANI nanofibers, Co0.5Zn0.5Fe2O4 ferrite nanocrystals undergo transition from being superparamagnetic to ferromagnetic. A mechanistic description of the process has also been presented in view that the process could be extended for the fabrication of other bimodal nanocomposites

Lattice Defects Induce Multiferroic Responses in Ce, La-Substituted BaFe0.01Ti0.99O3 Nanostructures

Single-phase multiferroic Ba(Fe0.67Ce0.33)(0.01)Ti0.99O3 (BFTO:Ce) and Ba(Fe0.67La0.33)(0.01)Ti0.99O3 (BFTO:La) nanostructures were synthesized by a hydrothermal method (180 degrees C/48h). Rietveld refinement of X-ray diffraction could confirm crystalline phase and lattice deformation by Ce, La into BFTO. The Ce and La doping induce nanoaggregation-type BFTO nanostructural product due to their ionic size effect and chemical behavior with OH- ions. Raman active modes show tetragonal phase and defects due to vacancies in the BFTO lattice. Photoluminescence spectrum involves multiple visible emissions due to defects/vacancies. The observed ferroelectric polarization is enhanced due to shape/size effect of nanoparticles, lattice distortion, and filling of d orbital in the perovskite BaTiO3. The room-temperature magnetic behavior is described due to antiferromagnetic interactions that strengthen by Ce and La doping. The zero-field cooling and field cooling magnetic measurement at 500Oe indicates antiferromagnetic to ferromagnetic transition. Dynamic magnetoelectric coupling was investigated, and maximum longitudinal magnetoelectric coefficient is 62.65 and 49.79mV/cmOe, respectively, measured for BFTO:Ce and BFTO:La. The magnetocapacitance measurements induce negative values that described in terms of magnetoresistance and magnetic phase transition effects. The influence of oxygen vacancy on multiferroicity is evaluated by valance states of O ions

Luminomagnetic K2Gd1-xZr(PO4)(3):Tb-x(3+) phosphor with intense green fluorescence and paramagnetism

Multimetallic complex phosphate K2Gd1-xZr(PO4)(3):Tb-x(3+) (0x50) synthesized by solid state diffusion exhibit intense green fluorescence and paramagnetic behaviour. Monophasic particles of dimensions ranging from few hundred nanometers to few micrometers could be obtained. Photo excitation at 274nm corresponding to Gd3+ transition(8)S(7/2)-I-6(J) and Gd3+-Tb3+ charge transfer followed by emission from D-5(J(J=3,4)) to F-7(J(J=3,4,5,6)) levels of Tb3+ ions is observed to be the most effective photoluminescence mechanism. Paramagnetic nature was proved by VSM study. Variation of paramagnetism in undoped K2GdZr(PO4)(3) and K2Gd1-xZr(PO4)(3):Tb-x(3+) particles and quantitative analysis by EPR indicate the role of unpaired 4f electron spin of trivalent rare earth ions in the lattice for making the particles paramagnetic

Synthesis, characterization and magnetic properties of monodisperse Ni, Zn-ferrite nanocrystals

Synthesization of monodisperse Ni, Zn-ferrite (Na1-xZnxFe2O4, x=1, 0.8, 0.6, 0.5, 0.4, 0.2, 0.0) nanocrystals has been achieved by the inverse microemulsion method using CURB as surfactant and kerosene as an oil phase. The detailed characterization of the synthesized nanocrystals and measurement of the magnetic properties has been done by techniques like X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM), Fourier transform infrared spectroscopy (FITR) and Vibrating Sample Magnetometer (VSM) respectively. The relationship between the structure and composition of the nanocrystals with magnetic properties has been investigated. The nanocrystals size is found to be in the range 1-5 nm. The effect of Zn substitution on size and magnetic properties has been studied It has been observed that magnetism changed from ferromagnetic at X=0 to super paramagnetic to paramagnetic at X=1 as Zn concentration increased. The Curie temperature is found to decrease with an increase in Zn concentration

Influence of Processing Methodology on Magnetic Behavior of Multicomponent Ferrite Nanocrystals

A novel and facile reverse microemulsion route has been developed for the synthesis of multicomponent ferrite nanocrystals, namely, Co0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4. In addition to microemulsions, these ferrite nanocrystals are also synthesized via a general chemical coprecipitation route. The crystals possess cubic spinel structure and spherical morphology as revealed by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and field emission transmission electron microscopy (FETEM) analysis. The average diameters of Co0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 nanocrystals obtained from chemical coprecipitation method are about 14 and 10 nm, respectively, and for those obtained from reverse microemulsion route they are calculated to be 5 and 2 nm, respectively. Vibrating sample magnetometery (VSM) reveals that the ferrite nanocrystals obtained from the reverse microemulsion route exhibit superparamagnetism whereas the ferrite nanocrystals obtained from chemical coprecipitation show ferromagnetism. The decrease in Curie (TC) and blocking (TB) temperature with size is attributed to the structural changes

Room-temperature multiferroic properties and magnetoelectric coupling in Bi4-x Sm (x) Ti3-x Co (x) O12-delta ceramics

We present the structural, dielectric, ferroelectric, magnetic and magnetoelectric studies of lead free; single phase Bi4-x Sm (x) Ti3-x Co (x) O12-delta (0 a parts per thousand currency sign x a parts per thousand currency sign 0.07) ceramics, synthesized using a standard solid-state reaction technique. Raman spectroscopy analysis reveals the relaxation of distortion in TiO6 octahedron. Field emission scanning electron microscopy confirmed the growth of plate-like grains. It is observed that with the substitution of Sm3+ and Co3+ ions the dielectric constant, loss tangent and ferroelectric transition temperature decreases. Electrical dc resistivity, remnant polarization and magnetization increases with increasing Sm3+ and Co3+ contents. The magnetoelectric coupling co-efficient, alpha = 0.65 mV cm(-1) Oe(-1) is realized for Bi4-x Sm (x) Ti3-x Co (x) O12-delta (x = 0.07) ceramic sample. Our results clearly demonstrate the lead free, multiferroic nature of Sm/Co-substituted Bi4Ti3O12, which may find useful application in designing cost-effective electromagnetic devices