Showing papers on "Magnetocapacitance published in 2008"
TL;DR: In this article, the magnetoelectric coupling in the lone pair containing piezoelectrics ferrimagnet Cu(2)OSeO(3) was investigated and it was shown that significant magnetocapacitance develops in the magnetically ordered state (T(c) = 60 K).
Abstract: We have investigated the magnetoelectric coupling in the lone pair containing piezoelectric ferrimagnet Cu(2)OSeO(3). Significant magnetocapacitance develops in the magnetically ordered state (T(c) = 60 K). We find critical behavior near T(c) and a divergence near the metamagnetic transition at 500 Oe. High-resolution x-ray and neutron powder diffraction measurements show that Cu(2)OSeO(3) is metrically cubic down to 10 K but that the ferrimagnetic ordering reduces the symmetry to rhombohedral R3. The metric cubic lattice dimensions exclude a magnetoelectric coupling mechanism involving spontaneous lattice strain, and this is unique among magnetoelectric and multiferroic materials.
128 citations
TL;DR: In this paper, the dielectric, ferroelectric, and magnetic properties of Bi5Ti3FeO15 bulk ceramic and thin film samples were measured using the sol-gel method.
Abstract: Bi5Ti3FeO15 bulk ceramic and thin film samples are prepared using the sol-gel method The dielectric, ferroelectric, and magnetic behaviors of these samples are measured in order to investigate the possible multiferroic effect The superparamagnetic behavior with dominant antiferromagnetic (AFM) interaction background for the as-prepared Bi5Ti3FeO15 samples is revealed The clearly identified magnetocapacitance effect at low temperature is argued to originate from the suppression of the AFM interaction by external magnetic field
118 citations
TL;DR: A new strategy to discover materials with large resistive or capacitive responses to magnetic fields is explored by synthesizing EuMO2N (M = Nb, Ta) perovskites that combine ferromagnetic order of S = 7/2 Eu2+ spins with possible off-center distortions of the d0 M5+ cations enhanced by covalent bonding to N.
Abstract: We have explored a new strategy to discover materials with large resistive or capacitive responses to magnetic fields by synthesizing EuMO2N (M = Nb, Ta) perovskites that combine ferromagnetic order of S = 7/2 Eu2+ spins with possible off-center distortions of the d0 M5+ cations enhanced by covalent bonding to N. EuNbO2N shows colossal magnetoresistances at low temperatures and a giant magnetocapacitance. However, the latter response originates from a microstructural effect rather than an intrinsic multiferroism.
87 citations
75 citations
TL;DR: It is demonstrated that magnetism is not necessary to produce a magnetocapacitance when the material is inhomogeneous and by considering a two-dimensional, two-component composite medium, a characteristic dielectric resonance that depends on magnetic field is found.
Abstract: The dielectric response in a magnetic field is routinely used to probe the existence of coupled magnetic and elastic order in the multiferroics. However, here we demonstrate that magnetism is not necessary to produce a magnetocapacitance when the material is inhomogeneous. By considering a two-dimensional, two-component composite medium, we find a characteristic dielectric resonance that depends on magnetic field. We propose this as a possible signature of inhomogeneities and we argue that this behavior has already been observed in nanoporous silicon and some manganites.
59 citations
TL;DR: In this article, the authors show that interfaces are the right way of increasing a coupling provided free charges are localized on these two-dimensional defects, and that the only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials.
Abstract: Triggered by the revival of multiferroic materials, a lot of effort is presently underway to find a coupling between a capacitance and a magnetic field. We show in this paper that interfaces are the right way of increasing such a coupling provided free charges are localized on these two-dimensional defects. Starting from commercial diodes at room temperature and going to grain boundaries in giant permittivity materials and to ferroelectric domain walls, a clear magnetocapacitance is reported which is all the time more than a few per cent for a magnetic field of 90 kOe. The only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials.
34 citations
TL;DR: In this article, the shape of the ferroelectric loop of a single crystal was investigated and it was shown that the shape strongly depends on magnetic field and temperature, while its dependence does not directly correlate with the magnetocapacitance effect before the paraelectric transition.
Abstract: The ferroelectric properties of ${\text{MnWO}}_{4}$ single crystal have been investigated. Despite a relatively low remanent polarization, we show that the sample is ferroelectric. The shape of the ferroelectric loop of ${\text{MnWO}}_{4}$ strongly depends on magnetic field and temperature. While its dependence does not directly correlate with the magnetocapacitance effect before the paraelectric transition, the effect of magnetic field on the ferroelectric polarization loop supports magnetoelectric coupling.
34 citations
TL;DR: Cr[(H(3)N-(CH(2))(2)-PO(3))(Cl)(H(2)O)] represents a rare example of a polar organic-inorganic hybrid material that exhibits a canted antiferromagnetic order below T(N)=5.5 K as mentioned in this paper.
Abstract: Cr[(H(3)N-(CH(2))(2)-PO(3))(Cl)(H(2)O)] represents a rare example of a polar organic-inorganic hybrid material that exhibits a canted antiferromagnetic order below T(N)=5.5 K. The unusual coexistence of a polar crystal structure and magnetic order triggered our investigation of the magnetodielectric coupling. The coupling is evidenced by an anomaly in the temperature dependence of the dielectric constant epsilon below the Neel temperature. The magnetocapacitance is enhanced by one order of magnitude below T(N). The main characteristics of the magnetodielectic response are interpreted by Landau theoretical coupling terms.
23 citations
TL;DR: In this article, the NSMO/Nb:STO junctions have been investigated and shown to have a built-in potential of 0.8-0.9eV.
Abstract: We have investigated epitaxial Nd0.5Sr0.5MnO3∕SrTi0.9998Nb0.0002O3(110) (NSMO/Nb:STO) junctions wherein a metal-insulator transition can be induced by magnetic field in the NSMO layer. The NSMO/Nb:STO junctions show highly rectifying current density–voltage (J-V) characteristics, in accord with the conventional theory for a Schottky (or a p-n) diode. The forward bias J-V, as well as the reverse bias capacitance-voltage characteristics, has revealed a built-in potential of 0.8–0.9eV. In the reverse bias region, a large positive magnetocapacitance has been observed at 5 and 50K, suggesting that the effective carrier density of NSMO is modified by the magnetic field.
21 citations
TL;DR: In this paper, the magnetocapacitance and relative permittivity of La1 − x − 1 − 1, 0.11 single crystals were found to be anomalous in the regime before the percolation threshold.
Abstract: Extremely high values of the relative permittivity up to 107 and the magnetocapacitance up to 105% have been found in La1 − x
Sr
x
MnO3 single crystals (x = 0.1, 0.11). These phenomena are observed even at room temperature. The observed behavior can be a consequence of the strong interaction among charge, spin, and lattice degrees of freedom, which leads to charge and phase separation in the regime before the percolation threshold.
15 citations
TL;DR: It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga (3+) into the Ba-Co-O system to stabilize Ba 6Ga 2Co 11O 26 and Ba 2GaCo 8O 14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O 3-delta] n.
Abstract: The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba−Co−O and Ca−Co−O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga3+ into the Ba−Co−O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3−δ]n[BaCo8O11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca3Co2O6 crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a...
TL;DR: In this paper, the steplike magnetocapacitance effect of one-dimensional spin frustrated compound Ca(3)Co(2)O(6) was investigated.
Abstract: The dielectric relaxation and magnetocapacitance effect of one-dimensional spin frustrated compound Ca(3)Co(2)O(6) are investigated. The steplike magnetocapacitance effect is observed and one to one corresponds to the steplike magnetization. We explain this phenomenon from the spin configuration dependent dielectric response. The simulation results using the Monte Carlo method are in good agreement with experimental data at low temperature. The close correspondence between the magnetic and dielectric properties indicates that the coupling is the intrinsic character of Ca(3)Co(2)O. The steplike magnetocapacitance effect may find potential applications in data storage and sensors. (C) 2008 American Institute of Physics.
TL;DR: In this paper, the capacitance characteristics of La 0.5Ca0.5MnO3∕Nb-SrTiO3 p-n junction and magnetic property have been investigated.
Abstract: The capacitance characteristics of La0.5Ca0.5MnO3∕Nb–SrTiO3 p-n junction and magnetic property have been investigated. The magnetic field-induced increase in ferromagnetic metallic phase, irreversibility, and the exchange bias effect were observed. The junction also shows a remarkable thermal hysteresis of capacitance, a giant positive magnetocapacitance (MC), a remarkable difference of MC for the zero field cooling and field cooling processes, and a memory effect of magnetic field. The results can be understood in terms of phase separation. This work demonstrates the remarkable tunability of the capacitance for phase separated manganite heterojunctions, which may have potential applications.
TL;DR: In this paper, the capacitance in these heterostructures varies with the applied magnetic field Appearance of magnetocapacitance and its dependence on temperature and magnetic field strength strongly indicated the possibility of strain mediated magnetoelectric coupling.
TL;DR: A superconducting layer exposed to a perpendicular electric field and a parallel magnetic field is considered within the Ginzburg-Landau (GL) approach in this paper, where the GL equation is solved near the surface and the surface energy is calculated.
Abstract: A superconducting layer exposed to a perpendicular electric field and a parallel magnetic field is considered within the Ginzburg-Landau (GL) approach. The GL equation is solved near the surface and the surface energy is calculated. The nucleation critical field of superconducting state at the surface depends on the magnetic and electric fields. Special consideration is paid to the induced magnetic-field effect cause d by diamagnetic surface currents. The latter effect is strongly dependent on the thickness of the sample. The effective inverse capacitance determines the effective penetration depth. It is found that the capacitance exhibits a jump at the surface critical field. An experiment is suggested for determining the change in the effective capacitance of the layer.
TL;DR: In this paper, the magnetic and dielectric properties of BaCo 2 Si 2 O 7 single crystal with a quasi-one-dimensional structure were investigated to explore novel magnetoelectric functionality.
Abstract: We have investigated the magnetic and dielectric properties of BaCo 2 Si 2 O 7 single crystal with a quasi-one-dimensional structure to explore novel magnetoelectric functionality. The Weiss temperatures estimated in paramagnetic region are - 20 K ( H ∥ c ) and - 74 K ( H ⊥ c ) , indicating the large magnetic anisotropy due to the highly anisotropic structure. The weak ferromagnetic magnetization rises up at 21 K, where the dielectric constant perpendicular to the c-axis decreases concomitantly. In addition, we have observed the magnetocapacitance effect below 21 K. Δ e ( H ) / e ( 0 ) reaches 0.2% at 5.5 K. These results suggest that there exists a substantial coupling between magnetism and dielectricity.
TL;DR: In this article, the magnetocapacitance characteristics of an epitaxial p-n heterojunction between magnetic InMnAs and InAs are investigated, and a large positive magnetocAP is observed at room temperature, which increases with reverse bias.
Abstract: The magnetocapacitance characteristics of an epitaxial p-n heterojunction between magnetic InMnAs and InAs are investigated. A large positive magnetocapacitance is observed at room temperature, which increases with reverse bias. For high reverse bias, the magnetocapacitance is linearly dependent on magnetic field. From capacitance-voltage measurements, the junction built-in voltage was determined and was observed to increase with magnetic field. The magnetocapacitance measurements support a model for a magnetic semiconductor heterojunction where spin-split polarized valence and conduction bands form due to the giant Zeeman effect.
TL;DR: In this paper, a multiferroic p-n junction was fabricated by growing La0.1Bi0.9MnO3 films on Nb-SrTiO3 using pulsed laser deposition.
Abstract: Multiferroic p-n junctions were fabricated by growing La0.1Bi0.9MnO3 films on Nb–SrTiO3 using pulsed laser deposition. The current-voltage curves of the junction show good rectifying property. Both the ferroelectric transition and ferromagnetic transition of La0.1Bi0.9MnO3 have remarkable influence on the transport properties of the junction. A large positive magnetocapacitance was also observed in this junction. Analysis suggests that the property of La0.1Bi0.9MnO3∕Nb–SrTiO3 is dominated by the property of La0.1Bi0.9MnO3. This work demonstrates that multiferroic p-n junctions possess some interesting properties that may be useful for future applications.
TL;DR: In this article, the behaviour of a magnetic core under a magnetic field and connected with an ac signal has been investigated, and the field induced change of the equivalent capacitance, ac resistance and impedance caused by that in the coil have been observed.
Abstract: The behaviour of a coil with a magnetic core under a magnetic field and connected with an ac signal has been investigated. The field induced change of inductance and the field induced change of the equivalent capacitance, ac resistance and impedance caused by that in the coil have been observed. By means of adding a loss film, which is placed at one end and vertical to the centre axis of the coil, all of those field induced changes of the parameters can approach or exceed 40% under a field less than 1600 Oe and with a signal frequency of 10 kHz.
TL;DR: In this article, the authors show that interfaces are the right way of increasing a coupling provided free charges are localized on these two-dimensional defects, and that the only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials.
Abstract: Triggered by the revival of multiferroic materials, a lot of effort is presently undergoing as to find a coupling between a capacitance and a magnetic field. We show in this report that interfaces are the right way of increasing such a coupling provided free charges are localized on these two-dimensional defects. Starting from commercial diodes at room temperature and going to grain boundaries in giant permittivity materials and to ferroelectric domain walls, a clear magnetocapacitance is reported which is all the time more than a few percent for a magnetic field of 90kOe. The only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials.
TL;DR: In this paper, the magnetocapacitance between a 2DEG and a gate electrode was investigated in a selectively doped n-AlGaAs/GaAs heterojunction with embedded InGaAs quantum dots (QDs).
Abstract: The magnetocapacitance between a two-dimensional electron gas (2DEG) and a gate electrode was investigated in a selectively doped n-AlGaAs/GaAs heterojunction with embedded InGaAs quantum dots (QDs). The complex capacitance C was studied as a function of the modulation frequency f ranging from 60 to 12 kHz at the filling factor ν= 2 of a Landau level. The experiment was well explained by a resistive plate model, where the bulk conductance σxx of the 2DEG has a frequency-dependent component proportional to fS (S = 0.51). This result suggests that the QDs induce potential valleys in a 2DEG channel, in which electron transfers occur between the valleys with their relaxation times extended over a wide range.
TL;DR: In this paper, the spin polarization of electrons trapped in InAs self-assembled quantum dot ensembles is investigated, and a statistical approach for the population of the spin levels allows one to infer the spin polarities from the measured values of the addition energies.
Abstract: The spin polarization of electrons trapped in InAs self-assembled quantum dot ensembles is investigated. A statistical approach for the population of the spin levels allows one to infer the spin polarization from the measured values of the addition energies. From the magnetocapacitance spectroscopy data, the authors found a fully polarized ensemble of electronic spins above 10T when B∥[001] and at 2.8K. Finally, by including the g-tensor anisotropy, the angular dependence of the spin polarization with the magnetic field B orientation and strength could be determined.
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TL;DR: In this article, a theoretical study of magnetocapacitance in a graphene monolayer at finite temperature taking into account the effects of disorder is presented, and the magnetic oscillations in the two systems are compared to those found in standard 2DEG systems.
Abstract: We present a theoretical study of magnetocapacitance in a graphene monolayer at finite temperature taking into account the effects of disorder. The density of states (DOS) and magnetocapacitance found for graphene are compared to those found in standard two dimensional electron gas (2DEG) systems. The magnetic oscillations in DOS and magnetocapacitance are found to be enhanced and much more robust with respect to temperature damping in monolayer graphene in comparison with a 2DEG. Furthermore, we find that there is a $\pi$ phase shift between magnetic oscillations in the two systems which can be attributed to Dirac electrons in graphene acquiring a Berry's phase as they traverse a closed path in a magnetic field.
TL;DR: In this paper, two ternary systems, Ba−Co−O and Ca−Co −O, have been chosen, and it has been shown that new phases with a complex triangular structure can be discovered, for instance, by introducing Ga3+ into the Ba−co−O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3−δ]n[BaCo 8O11].
Abstract: The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba−Co−O and Ca−Co−O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga3+ into the Ba−Co−O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3−δ]n[BaCo8O11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca3Co2O6 crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a...