Showing papers on "Magnetocapacitance published in 2017"

Large Magnetoelectric Coupling Near Room Temperature in Synthetic Melanostibite Mn2FeSbO6

Abstract: Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn2FeSbO6 (R3‾ space group) with ilmenite-type structure exhibits cation off-centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature.

Inverse Tunnel Magnetocapacitance in Fe/Al-oxide/Fe3O4.

Abstract: Magnetocapacitance (MC) effect, observed in a wide range of materials and devices, such as multiferroic materials and spintronic devices, has received considerable attention due to its interesting physical properties and practical applications A normal MC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel Here we report an inverse tunnel magnetocapacitance (TMC) effect for the first time in Fe/AlOx/Fe3O4 magnetic tunnel junctions (MTJs) The inverse TMC reaches up to 114% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Frohlich model (combined with the Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and −42%, respectively These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports They will open up broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices

Magnetoimpedance and magnetocapacitance of anion-substituted manganese chalcogenides

Abstract: The magnetoresistive effect in MnSe1−XTeX manganese chalcogenides with a substitute concentration of X = 0.1 is studied by impedance spectroscopy. The magnetoimpedance above the Neel temperature is found. The obtained experimental data are explained in the framework of the model of existence of magnetic nanoareas of two types. Two activation energies in the low- and high-frequency regions are determined from the frequency and temperature dependences of the permittivity described in the Debye model. The extrema found in the temperature dependence of the pyroelectric current are consistent with the maxima in the temperature dependence of magnetization. Temperature dependence of the carrier relaxation time is established. The magnetocapacitance of the MnSe1−XTeX solid solutions is found. The change in the carrier type above the Neel temperature and the temperature of the transition to the magnetically ordered state in the MnTe nanoarea is established.

Study on magnetocapacitance effect of magnetic particle polymer matrix composite system by finite element method

Abstract: In this paper, the magnetocapacitance effect of magnetic particles Fe3O4 embedded in polymer insulating matrix polydimethylsiloxane is investigated using finite element method by commercial software Comsol Multiphysics. With this method, the process of the capacitance variation under different magnetic field is simulated, and the factors influencing magnetocapacitance effect are studied. In particular, we apply the micro-macro coupling method for simulation analysis due to a large amount of calculation in the actual model. First, a three-dimensional microscopic model is calculated to obtain the effect of the magnetic field on the equivalent permittivity of the composite. The relationship is then substituted into the material property of the macroscopic model to simulate the magnetocapacitance effect. The results show that the composite exhibits magnetocapacitance characteristics that are related to the magnetic field intensity, particle size, and particle concentration. The capacitance value increases with the magnetic field at certain particle size and particle volume fraction. Meanwhile, the capacitance value at the same magnetic field increases with the particle size and particle volume fraction. The numerical results are consistent with the experimental results. The simulation model can provide a reference for research on the magnetocapacitance effect involving similar composite systems composed of magnetic particles and polymer matrix.

Magnetocapacitance in La 0.7 Sr 0.3 MnO 3 /Pb(Zr 0.2 Ti 0.8 )O 3 /La 0.7 Sr 0.3 MnO 3 multiferroic heterostructures

Abstract: Measurements of the magnetocapacitance effect in epitaxial La0.7Sr0.3MnO3/Pb(Zr0.2Ti0.8)O3/La0.7Sr0.3MnO3 heterostructures have been performed using a quasi-static method. Through capacitance-voltage measurements carried out under variable magnetic field it has been found that the magneto-capacitance depends on the orientation of the ferroelectric polarization. The value of magneto-capacitance can be as high as 1% in the voltage range near the ferroelectric coercive field. This has been attributed to a variation of the apparent built-in voltage of the PZT-LSMO Schottky barriers on applied magnetic field.

Magnetocapacitance and dissipation factor of epitaxial graphene-based quantum Hall effect devices

Abstract: We investigate the properties of the magnetocapacitance and dissipation factor of epitaxial graphene Hall bars with different electrode configurations to gain insight into the underlying physical mechanisms. The dependence of magnetocapacitance and dissipation factor on the magnetic field shows how the screening ability of the two-dimensional electron gas (2DEG) changes at the transition from the nonquantized to the quantized state. Both magnetocapacitance and dissipation factor exhibit a characteristic and correlated voltage dependence, which is attributed to the alternating contraction and expansion of the nonscreening 2DEG regions due to the alternating local electric field. Two regimes with seemingly different voltage dependencies are explained as the limiting cases of weak and strong electric fields of the same general voltage dependence. Electric fields in the plane of the 2DEG are found to cause about three orders of magnitude more ac dissipation than perpendicular electric fields. This strong directionality is attributed to the fact that the electrons are mobile in the plane of the 2DEG but are confined in the third dimension. In the quantized state, not only the screening edge of the 2DEG but also compressible puddles embedded in the bulk cause ac dissipation, as follows from the measured frequency dependence. Finally, characteristic parameters like the width of the screening edge, the threshold voltage, and the charging time of the compressible puddles are determined.

Influence of CoO Nanoparticles on Properties of Barium Zirconium Titanate Ceramics

Abstract: Composites of Ba(Zr0.07Ti0.93)O3 ceramic and CoO nanoparticles (at 1.0 vol.% to 3.0 vol.%) have been fabricated to investigate the effects of the CoO nanoparticles on the properties of the composites. X-ray diffraction data revealed that the modified samples contained Ba(Zr0.07Ti0.93)O3 and CoO phases. Addition of CoO nanoparticles improved the magnetic behavior and resulted in slight changes in ferroelectric properties. The composites showed a magnetoelectric effect in which the negative value of the magnetocapacitance increased with increasing CoO concentration. Examination of the dielectric spectra showed that the two phase-transition temperatures as observed for unmodified Ba(Zr0.07Ti0.93)O3 merged into a single phase-transition temperature for the composite samples. The composite samples also showed broad relative permittivity versus temperature (e r –T) curves with frequency dispersion. This dielectric behavior can be explained in terms of the Maxwell–Wagner mechanism. In addition, the Vickers hardness (H v) value of the samples increased with increasing CoO content.

Longitudinal magnetoconductivity and magnetodielectric effect in bilayer graphene

Abstract: It was recently shown that a finite imbalance between electron densities in the K and K' valleys of bilayer graphene induces a magnetoelectric coupling. Here we explore ramifications of this electronically tunable magnetoelectric effect for the optical conductivity and dielectric permittivity of this material. Our results augment current understanding of longitudinal magnetoresistance and magnetocapacitance in unconventional materials.

Method for preparing ferrite epitaxial thin film with indoor temperature broadband big magnetocapacitance effect

Abstract: The invention relates to a method for preparing a ferrite epitaxial thin film with an indoor temperature broadband big magnetocapacitance effect. The method comprises the first step of preparing the ferrite, wherein the component of the ferrite is represented by AFe12-xMxO19, A is one or more of Ba element or Sr element, M is one or more of Sc element, Mg element or Cr element, x is content of the M, and the range of the x is : 0

Inverse Tunnel Magnetocapacitance in Fe/Al-oxide/Fe 3 O 4

Abstract: Magnetocapacitance (MC) effect, observed in a wide range of materials and devices, such as multiferroic materials and spintronic devices, has received considerable attention due to its interesting physical properties and practical applications. A normal MC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (TMC) effect for the first time in Fe/AlOx/Fe3O4 magnetic tunnel junctions (MTJs). The inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Fröhlich model (combined with the Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and −42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open up broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.

Dielectric and magnetodielectric properties of Bi0.95Tb0.05Fe0.95Co0.05O3 nanoparticles

Abstract: Bi095Tb005Fe095Co005O3 (BTFCO) nanoparticles (NPs) have been prepared using a chemical sol-gel method and characterized by x-ray diffraction (XRD), dielectric and magnetodielectric measurements XRD pattern of the prepared sample shows all crystal planes of BiFeO3 (BFO) confirming successful preparation of the desired NPs Frequency dependent dielectric constant (er) curves exhibit an enhancement of cr in the BTFCO NPs in comparison with the pristine BFO sample Frequency dependent imaginary part of electric modulus curves exhibit a peak denoting presence of a relaxation process and activation energy obtained from Arrhenious fitting is found to be 034 eV Variation of magnetocapacitance in presence of magnetic field is stronger in BTFCO in comparison with the pristine BFO and it is a signature of increased magnetoelectric effect in the doped BFO

Electrically heterogeneous high dielectric BaTi 0.4 (Fe 0.5 Nb 0.5 ) 0.6 O 3 ceramic

Abstract: The effect of sintering temperatures on the lattice parameters, microstructure and electrical properties of BaTi 0.4 (Fe 0.5 Nb 0.5 ) 0.6 O 3 perovskite ceramics were investigated. Impedance spectroscopy analysis confirms that this material is electrically heterogeneous which plays a major role for the high dielectric constant. The sintering temperatures have a sensitive influence on the values of the dielectric constant. High dielectric constant (12,708) with low dielectric loss (0.23) was achieved at room temperature for 1250 °C sintered ceramic. Activation energy was found to be 0.25 eV and 0.31 eV corresponding to grain and grain boundary, respectively which confirms that the grain boundaries are more insulating than grains. We observed the high magnetocapacitance (5.8%) at 9 kOe for 1250 °C sintered sample which is useful for the practical application. This study will help to modify the BaFe 0.5 Nb 0.5 O 3 based materials and lead to more applications in the microelectronics devices.

Magnetodielectric coupling in Ferromagnetic/Ferroelectric/Ferromagnetic spin capacitor

Abstract: Ferromagnetic/Ferroelectric/Ferromagnetic (Ni/PZT/Ni) tri-layer artificial multiferroelectric structures in spin capacitor configuration were fabricated by sputtering ferromagnetic electrodes on PZT. Magnetocapacitance, magnetoimpedance, and phase angle measurements were carried out by a wide range of frequencies and magnetic fields at room temperature. We also compared the magnetodielectric measurements with Ni/PZT/Ag and Ag/PZT/Ag tri-layers structures. Ni/PZT/Ni spin capacitor shows a significantly different behavior compared to conventional PZT capacitor with Ag electrode and mixed electrode capacitor with one ferromagnetic and one conventional electrode.

Ferrite material with indoor temperature broadband high magnetocapacitance effect and preparation method thereof

Abstract: The invention relates to a ferrite material with indoor temperature broadband high magnetocapacitance effect and a preparation method thereof; the ferrite material has a molecular formula of AFe12-xMxO19, wherein A is at least one of Ba or Sr, M is at least one of Sc, Mg or Cr, and x is atomic specific content of M with 0