NiFe2O4 Research Articles

Ordered arrays of multiferroic epitaxial nanostructures.

Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe2O4 (NFO) and FE PbZr0.52Ti0.48O3 or PbZr0.2Ti0.8O3, with large range order and lateral dimensions from 200 nm to 1 micron.MethodsThe structures were fabricated by pulsed-laser deposition. High resolution transmission electron microscopy and high angle annular dark-field scanning transmission electron microscopy were employed to investigate the microstructure and the epitaxial growth of the structures. Room temperature ferroelectric and ferrimagnetic domains of the heterostructures were imaged by piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), respectively.ResultsPFM and MFM investigations proved that the hybrid epitaxial nanostructures show ferroelectric and magnetic order at room temperature. Dielectric effects occurring after repeated switching of the polarization in large planar capacitors, comprising ferrimagnetic NiFe2O4 dots embedded in ferroelectric PbZr0.52Ti0.48O3 matrix, were studied.ConclusionThese hybrid multiferroic structures with clean and well defined epitaxial interfaces hold promise for reliable investigations of magnetoelectric coupling between the ferrimagnetic / magnetostrictive and ferroelectric / piezoelectric phases.

Raman study of NiFe2O4 nanoparticles, bulk and films: effect of laser power

AbstractNanoparticles, bulk and thin films of NiFe2 O4 compounds are studied by micro‐Raman spectroscopy. The effect of varying the incident laser power up to 40 mW was studied in all forms of the samples. The spectra showed a large magnitude of red shift and line broadening as a result of high incident laser power. It is shown that the inverse spinel structure remains robust, and no trace of laser‐induced oxidation was observed. The low‐temperature study of the bulk and nanoparticles has also been carried out for elucidating thermal effects due to the high incident laser power. The rise in temperature for maximum incident laser power of 40 mW was estimated to be ∼625 °C. Copyright © 2010 John Wiley & Sons, Ltd.

Electric-field-control of magnetic remanence of NiFe2O4 thin film epitaxially grown on Pb(Mg1/3Nb2/3)O3–PbTiO3

We propose an asymmetric bilayer structure in which the magnetic remanence (MR) is controlled by the in-plane strain of the top NiFe2O4 (NFO) layer epitaxially constrained by the bottom Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrate. In this asymmetric structure, an electric-field-induced giant piezoelectric strain from the bottom PMN-PT layer is effectively transferred to the top NFO layer. We have shown that the room-temperature magnetic remanence (MR) of the 100-nm-thick NFO layer is enhanced by 46% when an electric-field-induced in-plane compressive strain is about −0.1%. Synchrotron x-ray absorption near edge structure study supports a scenario of the cation-charge redistribution between Ni2+ and Fe3+ ions under the condition of an electric-field-induced in-plane compressive strain.

Dielectric, magnetic and magnetoelectric properties of multiferroic BiFe0.5Cr0.5O3–NiFe2O4 composites

Multiferroic composites of NiFe2O4 (NFO) and BiFe0.5Cr0.5O3 (BFCO) are synthesized and their dielectric, magnetic, and magnetoelectric (ME) properties are measured at room temperature. NFO-BFCO forms a two-phase composite. The composite has a larger magnetization and dielectric constant than those of both parent compounds, due to the effects of interfacial strain on BFCO. Furthermore, the ME response in NFO-BFCO is about one time larger than that of BFCO, revealing the success of magnetic control of the dielectric response via the mechanical coupling, which can be exploited in the future applications of multiferroic composites.

Kinetics of Thermal Decomposition of Ammonium Perchlorate with Nanocrystals of Binary Transition Metal Ferrites

AbstractBinary transition metal ferrite (BTMF) nanocrystals of formula MFe2O4 (M=Cu, Co, Ni) were prepared by the coprecipitation method and characterized by X‐ray diffraction (XRD). XRD patterns gave average particle size by using Scherrer's equation for CuFe2O4 (CuF), CoFe2O4 (CoF), and NiFe2O4 (NiF) as 39.9, 27.3, and 43.8 nm, respectively. The catalytic activity measurements on the thermal decomposition of ammonium perchlorate (AP) were carried out by using thermogravimetry (TG), differential thermal analysis (DTA), and ignition delay studies. Isothermal TG data up to a mass loss of 45% have been used to evaluate kinetic parameters by using model fitting as well as isoconversional method. The order of catalytic activity was found to be:

Magnetoelectric properties of core-shell particulate nanocomposites

In this study, we report results on magnetoelectric (ME) core-shell Pb(Zr,Ti)O3 (PZT)-NiFe2O4 (NF) particulate nanocomposites. NF particles forming the shell had size in range of 20–30 nm. The grain size of sintered nanocomposites was found to be in the range of 500–800 nm. The sintered nanocomposite exhibited piezoelectric coefficient (d33) of 60 pC/N, dielectric constant of 865, and ME coefficient of 195 mV/cm Oe. High ME coefficient was observed for wide range of dc bias magnetic field. This approach of fabricating layered composite has a promise to provide large ME coefficients in particulate sintered structures.

Multiferroic behaviour of epitaxial NiFe2O4–BaTiO3 heterostructures

Multiferroic NiFe2O4 (NFO)-BaTiO3 (BTO) bilayered thin films are epitaxially grown on (001) Nb-doped SrTiO3 (STO) substrates by pulsed-laser deposition (PLD). Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with (001)-orientation, i.e. (001)-NFO/(001)-BTO/substrate and (001)-BTO/(001)-NFO/substrate. Microstructure studies from x-ray diffraction (XRD) and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious mag-netoelectric (ME) effect on coupling response.

DIELECTRIC AND FERROELECTRIC BEHAVIORS OF NOVELPbTiO3/NiFe2O4THIN FILMS PREPARED BY SOL–GEL METHOD

Ferroelectric/ferromagnetic (ME) biphase composite thin films with the type of (1–x) PbTiO3( PT )–x NiFe2O4(NFO) (x = 1–9) were successfully formed in situ by sol–gel process. The dielectric and ferroelectric behaviors of the composite thin films were investigated. The asymmetrical hysteresis loops of the composite arise from the leak current due to low resistivity of NFO. The stronger stress in the thin films due to the strong conjunction between PT and the substrate contributes to the increase (decrease) of the coercive force (the remanent polarization) with increasing the content of PT. The ME composites exhibit slight percolation effect. The high dielectric constant near the percolation threshold is attributed to the "micro-capacitors" in the composite thin films.

Magnetoelectric composite ceramics of nickel ferrite and lead zirconate titanate via in situ processing

Magnetoelectric (ME) composite ceramics of NiFe2O4 (NFO) and lead zirconate titanate (PZT) were synthesized by a simple in situ processing based on a sol–gel method followed by a conventional sintering. X-ray diffraction patterns and scanning electron microscopy images revealed that this processing can produce two pure phases simultaneously. The in situ grown magnetic NiFe2O4 grains were well dispersed in the PZT matrix. The results demonstrated an attractive ME response of about 28.5 V cm−1 Oe−1 in the 0.35 NiFe2O4/0.65PZT at a resonance frequency of around 287 kHz.

Preparation of Composite Ceramics of NiFe<sub>2</sub>O<sub>4</sub>/PZT by Sol-Gel Method and their Magnetoelectric Effect

The precursor powder of lead-zirconate-titanate (PZT) and NiFe2O4 (NFO) was prepared using one step sol-gel method. The dry powders got after a series of processes were sintered via a conventional ceramic solid-state reaction technique. All the diffraction peaks in the XRD patterns of the composites can be readily indexed to NFO and PZT, respectively. The SEM micrograph shows two different phases of PZT and NFO distinctly and the particle size of NFO was about 2~4 μm. The magnetoelectric (ME) coefficient, dielectric constant, piezoelectric constant, magnetic hysteresis loops of the samples were measured. The dc magnetic Hdc resulting in the maximum ME coefficient varies from 0.65kOe to 1.0kOe with the increase of the NFO volume fraction. The maximum magnetoelectric coefficient of 6.15Vcm-1Oe-1 was obtained at resonance frequency of 289.8kHz, dc magnetic intensity of 0.8kOe and NFO volume fraction of 0.25.

Spin filtering through ferrimagnetic NiFe2O4 tunnel barriers

We report experiments of spin-filtering through ultrathin insulating layers of the high Curie temperature ferrimagnetic oxide NiFe2O4 (NFO). The spin-filtering efficiency of electrons tunneling from a gold electrode through NFO is analyzed with a counter-electrode of La2∕3Sr1∕3MnO3 (LSMO). We measure a tunnel magnetoresistance of 40%–50% when the configuration of the magnetizations of the NFO and LSMO goes from parallel to antiparallel. This value corresponds to a spin-filtering efficiency of up to 22% by the NFO barrier. We discuss the sign and temperature dependence of the spin-filter effect and argue that our results show the potential of spinel ferrites for spin-filtering and injection.

Fabrication of NiFe2O4 nanowire arrays and its magnetic properties

Arrays of NiFe2O4 nanowires were prepared by using porous anodic al uminum oxide(AAO) membrane as the template. For the preparation of the ferrite n anowires, Ni_Fe alloy nanowires were electrodeposited into the pores of the AAO membranes. The atomic ratio is about Ni∶Fe=1∶2 which can be detected by engerg y dispersive spectroscopy. X-ray diffraction study showed the pure phase of NiFe 2O4 after anodization. SEM and TEM studies showed the diameters of t he pores and the nanowires are all about 70nm. The vibrating sample magnetometer studies of the nanowire arrays showed the anisotropic magnetic properties befor e and after anodization. Coercivity and squareness ratio have been improved appa rently in the NiFe2O4 nanowires arrays.

Molecular-field coefficients of MnFe2O4 and NiFe2O4 spinel ferrite systems

Calculated thermomagnetization curves for MnFe2 O4 and NiFe2 O4 have been matched to reported experimental results. Since both Mn2+ and Ni2+ ions are also strongly exchange coupled to the Fe3+ ions, separate sets of molecular-field coefficients were determined for each of these interactions and then averaged into the basic two-sublattice solution. For the usual case with 80% of the manganese in tetrahedral (A) sites, the ratios of coefficients determined from the fit to experiment agree closely with the values found from high-temperature susceptibility measurements, with ‖NAA /NAB‖ = 0.840 and ‖NBB /NAB‖ =0.295. For Ni ferrite, these ratios exceed those determined from magnetic susceptibilty measurements, suggesting an intrasublattice exchange for nickel that is stronger than previously considered. Calculations of magnetic dilution effects in both the manganese and nickel families show good accuracy for a practical range of Zn2+ substitutions in A sites.

The formation of nickel ferrite

Abstract The preparation of nickel ferrite in the solid state reaction NiO + Fe2O3 → Ni Fe2O4 is preceeded by the formation of an intermediate oxygen deficient material. Although X-ray powder photographs have not revealed a separate phase, neither the magnetic properties nor the oxygen affinity of the material corresponds to that of the initial materials or the finial product.