Showing papers on "Magnetocapacitance published in 2005"

Magnetodielectric effect without multiferroic coupling

Abstract: The existence of a magnetodielectric (magnetocapacitance) effect is often used as a test for multiferroic behavior in new material systems. However, strong magnetodielectric effects can also be achieved through a combination of magnetoresistance and the Maxwell-Wagner effect, unrelated to multiferroic coupling. The fact that this resistive magnetocapacitance does not require multiferroic materials may be advantageous for some practical applications. Conversely, it also implies that magnetocapacitance per se is not sufficient to establish multiferroic coupling.

Magnetocapacitance and exponential magnetoresistance in manganite–titanate heterojunctions

Abstract: We present a rectifying manganite–titanate heterojunction exhibiting a magnetic field tunable depletion layer. This creates a large positive magnetocapacitance, a direct measure of the field-induced reduction of the effective depletion width across the junction. Furthermore, the reduction of the junction barrier shifts the forward bias characteristics, giving exponentially enhanced differential magnetoresistance, occurring despite the absence of a spin filter. These results provide a unique probe of a Mott insulator∕band insulator interface, and further suggest electronic devices incorporating the magnetic field sensitivity of these strongly correlated electron materials.

Magnetocapacitance effect in perovskite-superlattice based multiferroics

Abstract: We report the structural and magnetoelectrical properties of La0.7Ca0.3MnO3∕BaTiO3 perovskite superlattices grown on (001)-oriented SrTiO3 by the pulsed laser deposition technique. Magnetic hysteresis loops, together with temperature dependent magnetic properties, exhibit well-defined coercivity and magnetic transition temperature (TC) ∼140K. dc electrical studies of films show that the magnetoresistance (MR) is dependent on the BaTiO3 thickness, and negative MR as high as 30% at 100K are observed. The ac electrical studies reveal that the impedance and capacitance in these films vary with the applied magnetic field due to the magnetoelectrical coupling in these structures—a key feature of multiferroics. A negative magnetocapacitance value in the film as high as 3%pertesla at 1kHz and 100K is demonstrated, opening the route for designing novel functional materials.

Magnetocapacitance effect in perovskite-superlattice based multiferroics

Abstract: We report the structural and magnetoelectrical properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$/BaTiO$_3$ perovskite superlattices grown on (001)-oriented SrTiO$_3$ by the pulsed laser deposition technique. Magnetic hysteresis loops together with temperature dependent magnetic properties exhibit well-defined coercivity and magnetic transition temperature (T$_C$) \symbol{126}140 K. $DC$ electrical studies of films show that the magnetoresistance (MR) is dependent on the BaTiO$_3$ thickness and negative $MR$ as high as 30% at 100K are observed. The $AC$ electrical studies reveal that the impedance and capacitance in these films vary with the applied magnetic field due to the magnetoelectrical coupling in these structures - a key feature of multiferroics. A negative magnetocapacitance value in the film as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for designing novel functional materials.

Magnetocapacitance probing of the many-particle states in InAs dots

Abstract: We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasiparticle wave functions in momentum space for one to two electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high-energy orbitals exhibit signatures of anisotropic confinement and correlation effects.

Magnetocapacitance effect and related microstrucuture in Ti-doped Y Mn O 3

Abstract: We have investigated microstructures giving rise to magnetocapacitance effect in Ti-doped $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ $(\mathrm{Y}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3})$ by both electron diffraction and real-space imaging techniques. Diffuse scattering elongating along the [110] direction due to the instability of the Mn trimerization were found in the $x=0.175$ compound, which exhibits the enhanced magnetocapacitance effect. With increasing Ti concentration, the centrosymmetric (paraelectric) $R\overline{3}c$ phase grows up at the expense of the ferroelectric $P{6}_{3}cm$ phase around $x=0.20$ and the $R\overline{3}c$ phase is dominant above $x=0.30$. Our present results indicate that the Mn trimers with the short-range correlation inside the ferroelectric nanodomains with the $10--20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ size should be responsible for the enhancement of the magnetocapacitance and, on the other hand, the appearance of the $R\overline{3}c$ phase suppressed the magnetocapacitance effect.

Effect of ferroelectric layers on the magnetocapacitance properties of superlattices-based oxide multiferroics

Abstract: A series of superlattices composed of ferromagnetic La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO) and ferroelectric/paraelectric Ba$_{1-x}$Sr$_x$TiO$_3$ (0$\leq $x$\leq $1) were deposited on SrTiO$_3$ substrates using the pulsed laser deposition. Films of epitaxial nature comprised of spherical mounds having uniform size are obtained. Magnetotransport properties of the films reveal a ferromagnetic Curie temperature in the range of 145-158 K and negative magnetoresistance as high as 30%, depending on the type of ferroelectric layers employed for their growth (\QTR{it}{i.e.} '\QTR{it}{x'} value). Ferroelectricity at temperatures ranging from 55 K to 105 K is also observed, depending on the barium content. More importantly, the multiferroic nature of the film is determined by the appearance of negative magnetocapacitance, which was found to be maximum around the ferroelectric transition temperature (3% per \QTR{it}{tesla}). These results are understood based on the role of the ferroelectric/paraelectric layers and strains in inducing the multiferroism.

Spin gap in the two-dimensional electron system ofGaAs∕AlxGa1−xAssingle heterojunctions in weak magnetic fields

Abstract: We study the interaction-enhanced spin gaps in the two-dimensional electron gas confined in $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ single heterojunctions subjected to weak magnetic fields. The values are obtained from the chemical potential jumps measured by magnetocapacitance. The gap increase with parallel magnetic field indicates that the lowest-lying charged excitations are accompanied with a single spin flip at the odd-integer filling factor $\ensuremath{ u}=1$ and $\ensuremath{ u}=3$, in disagreement with the concept of skyrmions.

Evidence of a strong magnetic effect on the impedance of integrated piezoelectric resonators

Abstract: In the vicinity of their resonance frequency, piezoelectric resonators are highly sensitive to small perturbations. The present report is focused on the magnetic field as a perturbation source. Magnetocapacitance modulation of more than 5% is achieved at room temperature on both ferroelectric single crystals and quartz disks. Since such piezoelectric resonators are now available as membranes directly integrated on a silicon wafer, we have checked the magnetocapacitance modulation in such resonators. We show here that a moderate magnetic field of 2×104 Oersteds is able to efficiently tune the impedance of these resonators in their resonance window.

Magnetocapacitance in Geometrically Frustrated Magnet ZnFe2O4

Abstract: We report the measurement of dielectric constant in ZnFe 2 O 4 as a function of temperature and magnetic field. The behavior of dielectric constant for single crystals, which is dominated by the pa...

Structural Phase Transition and Domain Structures in YMn1-xTixO3

Abstract: We investigated changes in domain structures induced by a partial substitution of Ti for Mn in multiferroic YMnO3 by transmission electron microscopy (TEM) In the ferroelectric phase of YMnO3 at room temperature, there exist 180-degree ferroelectric (FE) domain structures of a micrometer size On substituting Ti for Mn, the size of FE domains becomes fragile and, at approximately x=0175 in YMn1-xTixO3, the size can be estimated to be 10–20 nm On further substitution, it is found that a structural phase transition from a hexagonal P63 cm structure to a new rhombohedral R3c one takes place at approximately x=020 In YMn1-xTixO3 with 020

Gigantic magnetocapacitance and magnetostriction in ferroelectric antiferromagnet GdMnO/sub 3/

Abstract: In this work, gigantic magnetocapacitance effect and magnetostriction in GdMnO/sub 3/ were reported to demonstrate the direct evidence for strong mutual coupling among spin, localized charge, and lattice degrees of freedom. The results clearly indicate a direct correlation between the magnetic and dielectric properties of the material. Also, it was concluded that magnetostriction is not a major origin of the observed gigantic magnetocapacitance. The observed coupling among magnetic, dielectric, and lattice structural properties may bring a possible multifunctional device in the future.