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The effect of structural stacking sequence on magnetocaloric, critical behavior and dielectric properties in the nanocrystalline Ba1-xSrxCo0.9Mn0.1O3-δ (0 ≤ x ≤ 0.5) system has been investigated. The parent BaCo0.9Mn0.1O3-δ compound exhibit 12H-hexagonal phase. With increase in Sr-doping, structure changes to 2H-phase (x = 0.5) through mixed 12H+2H-phase (x = 0.1 and 0.3) for the samples annealed at 1100 °C. The magnetocaloric properties shows promising results in the presence of 12H-phase, whereas, inclusion of 2H-phase suppresses magnetocaloric properties. The maximum entropy change for a field change of 5 T is found to be 2.50, 1.73, 0.50 and 0.12 Jkg-1K−1 for x = 0.0, 0.1, 0.3 and 0.5 respectively. The field dependence of maximum entropy change under different composition ratio is studied using phenomenological scaling behavior of magnetic entropy change model. The nature of magnetic phase transition and critical behavior of the nanocrystalline system are studied using Landau theory and Arrot plots. The obtained critical exponents show deviation from mean-field model with increase in Sr-doping. In addition, influence of structural changes on temperature and field dependent dielectric properties is studied. The temperature variation of dielectric constant (e′) shows subtle change in the vicinity of magnetic transition and the numerical value of e’ suppresses with 2H-phase. The value of magnetocapacitance (MC %) is also get suppressed while going mixed 12H+2H- to 2H-phase. The origin of magneto-dielectric properties in the present nanocrystalline system demonstrates the strong correlation among structural, magnetic, electrical and dielectric properties.

BiFeO3 is an attractive multiferroic ceramic for device application. The magnetoelectric coupling coefficient (αE ~ 2.2 mV/cm-Oe) of single-phase BiFeO3 ceramic is denominated here, which is calculated by theoretical method (by using the numerical value of capacitance) in place of direct measurement of voltage. An applied magnetic field raises the capacitance of the pellet of BiFeO3; analogous change in voltage gives the values of magnetoelectric coupling coefficient. Moreover, using the Ginzburg-Landau theory, the magnetoelectric interaction constant (γ) was calculated around ~ 9.3 × 10−1, which is numerically two times lower than the magnetoelectric coupling coefficient. This theoretical cum experimental study is very important in the view point of science and devices.

This communication presents the dielectric and magnetodielectric studies of Bi 3.7 Sm 0.3 Ti 2.7 Fe 0.3 O 12 ceramic samples synthesized by a conventional solid state reaction method. X-ray diffraction (XRD) patterns reveal the formation of single phase orthorhombic structure. Dielectric measurements have shown anomalous behavior around 150 °C. Dielectric modulus analysis confirms the non-Debye type relaxation behavior at higher temperature. Room temperature weak ferromagnetism has been observed for Sm/Fe modified bismuth titanate ceramic with 2 M r value of 5.4×10 −3 emu/g. Magnetodielectric measurement shows the variation in dielectric constant value with applied magnetic field of 5 T, which confirms the magnetodielectric coupling in the system. The present results suggest a new material for room temperature multiferroic applications.

Nanocrystalline samples of gallium orthoferrite (GaFeO3, GFO) and Zn doped GaFeO3 (Ga0.95Zn0.05FeO3, GZFO1 and Ga0.90Zn0.10FeO3, GZFO2) are prepared by sol–gel method. Crystallographic phase of each sample has been confirmed by analyzing the X-ray diffractogram using FULLPROF program and all the samples are grown in the distorted perovskite type structure. Magnetic measurements of all the samples are carried out in the temperature range of 300–4 K. Dielectric and ferroelectric measurements of the samples are also carried out at room temperature. Interestingly, the magnetization and electric polarization of the doped samples are enhanced compared to those of the pristine sample of GFO. The dielectric constant measured in presence and absence of a magnetic field confirmed that all the samples (GFO, GZFO1, and GZFO2) are type-II multiferroics and the magnetocapacitance is enhanced in the doped samples. The simultaneous enhancement of magnetization, polarization and magneto-capacitance co-efficient of the doped samples compared to that of GFO will be quite interesting for applications in electronic and memory devices.

The non-polar material SeCuO3, which contains Cu2+ with S = 1 / 2 spin and Se4+, has a highly distorted perovskite structure due to the small radii of Se4+ cations. The dielectric constant displays a critical decrease at 25 K, at which temperature the ferromagnetic ordering of the Cu2+ spin appears, suggesting a strong coupling between the magnetic and dielectric properties. Studies on SeCuO3 show that the magnetic and electrical subsystems reciprocally correlate via the hybridization of sp and pd. We conclude that the spin–pair correlation along the b-axis plays a significant role in the decrease of the dielectric constant around the magnetic transition temperature via the magnetoelectric coupling, and successfully explain the dielectric anomaly. The obtained dielectric constant and the magnetocapacitance for SeCuO3 are quantitative agreement with experimental results.

The mixed spinel–perovskite composites of x MnFe 2 O 4 –(1– x )BiFeO 3 with x =0, 0.1, 0.2, 0.3 and 0.4 were prepared by solid state reaction method. The structure and grain size were examined by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD results showed that the composites consisted of spinel MnFe 2 O 4 and perovskite BiFeO 3 phases after being calcined at the temperature 950 °C for 2 h. The grain size ranged from 0.8 to 1 μm. Magnetization was found to increase with increasing concentration of ferrite content. The variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Magnetocapacitance was also observed in the prepared composites, which may be the sign of magnetoelectric coupling in the synthesized composites at room temperature.

Multiferroic nanoceramics BiFe 1− x Ni x O 3 (where x =0, 0.15, 0.20, and 0.25) were prepared by the sol–gel method. XRD analysis of samples calcined at a low temperature of 400 °C for 2 h shows the formation of a single phase perovskite rhombohedral structure. Average particle size was observed to be ∼50 nm by TEM measurement. Magnetization was found to increase with increase in the concentration of Ni. Dielectric constant and dielectric loss were measured up to 1 MHz frequency. Variation of dielectric constant with temperature shows a peak at ∼395 °C (Neel temperature) for x =0.15 and the peak shifts towards lower temperature at a higher concentration of Ni with diffused type of phase transition. Magnetocapacitance was found to decrease with magnetic field. For BiFe 1− x Ni x O 3 (with x =0.15, 0.20, 0.25) nanoceramics, the fractional change of the magnetic field induced a change in the dielectric constant, which may well be approximated by Δ e / e = γM 2 , (where γ (magnetoelectric interaction ) is small and negative). A linear fit gave the value of γ of ∼−2.14×10 −3 , −2.11×10 −3 , and −2.09×10 −3 for BiFe 1− x Ni x O 3 nanoceramics, with x =0.15, 0.20, and 0.25, respectively.

Spinel-perovskite nanocomposites of xCrFe2O4–(1−x)BiFeO3 with x=0.0, 0.1, 0.2, 0.3, 0.4 were prepared by sol gel method. The XRD showed the phase formation of nanocomposites at 700 °C. Particle size was observed to be ∼100 nm by TEM. The variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Magnetization was found to increase with increasing concentration of ferrite content. Dielectric analysis showed the conducting behaviour at higher temperature. Magnetocapacitance was also observed in the prepared nanocomposites which may be the sign of magnetoelectric coupling in the synthesized nanocomposites at room temperature.

We have investigated the width of the compressible strips in the edge state by magnetocapacitance between two-dimensional electron gas and a metal gate. The detail of Landau level filling factor dependence of the width is measured around the quantum Hall plateaux, and the influence of confinement potential on the width has been studied by tuning the side gate voltage. It is confirmed that the width is mainly governed by the depletion region at the sample boundary; the spatially gentle confinement potential forms wider compressible and incompressible strips. The nonlocal resistance has been also studied in the samples with tunable confinement potential by side gate, which supports the result of the capacitance measurement.

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.

We have evaluated the width of edge channels in the fractional and integer quantum-Hall (QH) regime by the magnetocapacitance measurement between a gate and two-dimensional electron system in GaAs/AlGaAs heterostructures. The frequency dependence of the magnetocapacitance between 100 Hz and 1 MHz has been measured at temperatures between 35 mK and 0.4 K. At the fractional QH regime, the total width of the edge channels is found to be 2.5 and 9 μm at 35 mK at the QH plateaux of filling factor ν= 1 3 and 2 3 , respectively. In the integer QH regime, the temperature dependence of the edge channel width is almost flat in the range of 35 mK–0.4 K. At the QH plateau of ν=1 due to spin-splitting Landau level, the width of total edge channel is almost the same value with that at ν=2. The width at ν=3 is also comparable to that at ν=4, although the residual bulk conductivity of ν=3 is an order of magnitude larger than that of ν=4.

The stability of a two-dimensional electron system with negative compressibility is discussed and related to experimental data from magnetocapacitance measurements. A system with a single Landau level as well as one with several Landau levels is investigated.

We have investigated the bulk conductivity (σxx) of two-dimensional electron gas in GaAs/AlGaAs heterostructure in the quantum Hall regime by the magnetocapacitance measurement with Corbino geometry sample. The σxx at the Hall plateau down to 10−11 S is measured, and the temperature dependence of σxx is discussed. The experimental characteristics of the capacitance measurement is also discussed.

By measuring the magnetocapacitance of high-mobility Si-MOSFET's, we have found that the thermodynamic density of states of a two-dimensional electron gas may become negative in high magnetic fields and at low temperatures. The effect seems to be due to the interactions between electrons.