We report electrical, magnetic, magnetodielectric and magnetoabsorption properties of a polycrystalline GaFeO3. The resistivity measurement shows that the sample is highly insulating below 200 K and the resistivity above 200 K obey the Arrhenius law with an activation energy of Ea = 0.67 eV. An anomaly occurs in the temperature dependence of permittivity (e) near the ferrimagnetic transition temperature (TC = 228 K) in a zero magnetic field and it is suppressed under H = 60 mT which indicates a possible magnetoelectric coupling in GaFeO3 with a fractional change of de/e = -1.8% at 60 mT around TC. The coercivity (HC) of the sample increases dramatically with lowering temperature below 200 K from 0.1 T at 200 K to 0.9 T at 5 K. Magnetoabsorption was studied with a LC resonance technique and we found a close correlation between the shift in the resonance frequency due to applied magnetic field and the coercive field measured using dc magnetization measurements. Our results obtained with multiple techniques suggest that GaFeO3 is an interesting ferrimagnet with potential applications in future multiferroic devices.
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.
We report the results of detailed investigations of magnetization, heat-capacity, dielectric, pyrocurrent, and magneto(di)electric measurements on Tb2BaCoO5, belonging to a hither-to-unexplored spin-chain cobaltates family, R2BaCoO5 (R= Rare-earths). The magnetic measurements reveal that this compound exhibits an antiferromagnetic transition at (T_N=) 18.8 K and there is a spin-reorientation beyond 40 kOe below T_N. Dielectric and pyrocurrent data measured as a function of temperature and magnetic-field establish that this compound is a type-II multiferroic material. The most fascinating findi…
Multiferroicity and magnetodielectric coupling in metal-organic-frameworks (MOFs) is rare and so far restricted mainly to formate-based systems with perovskite structure. In the course of this work we designed a tetragonal framework [Co(C16H15N5O2)], exhibiting spin-chains of Co2+ ions, which are bridged by an organic linker containing a dipolar nitrobenzene moiety. This compound shows relaxor-like ferroelectricity at 100 K, which is followed by the onset of complex magnetic order at 15 K, indicative of weak ferromagnetism. The clear anomaly of the dielectric constant at the magnetic ordering …
We report the results of our investigation of magnetic, thermodynamic and dielectric properties of Ca substituted half-doped orthochromite, Dy0.6Ca0.4Fe0.5Cr0.5O3. Magnetic susceptibility and heat capacity data bring out that this compound undergoes two antiferromagnetic transitions, one at ~132 and the other at ~22 K. These values are higher than those of DyFe0.5Cr0.5O3. This finding highlights that non-magnetic hole doping in form of Ca+2 in the place of magnetic Dy+3 tends to enhance magnetic transition temperatures in this half-doped orthochromite. We attribute it to possible change in the…
BFO3 ceramics were investigated by means of infrared reflectivity and time domain THz transmission spectroscopy at temperatures 20 - 950 K, and the magnetodielectric effect was studied at 10 - 300 K, with the magnetic field up to 9 T. Below 175 K, the sum of polar phonon contributions into the permittivity corresponds to the value of measured permittivity below 1 MHz. At higher temperatures, a giant low-frequency permittivity was observed, obviously due to the enhanced conductivity and possible Maxwell-Wagner contribution. Above 200 K the observed magnetodielectric effect is caused essentially…
Magnetoelectric coupling in the polycrystalline antiferromagnets CuFe0.95Rh0.05O2 and CuFeO2 has been investigated. For both samples, electric polarization was observed in the absence of an applied external magnetic field demonstrating that for multiferroic research ceramics are worth to be studied. The observed magnetodielectric effect for CuFe0.95Rh0.05O2 in the electrically polar phase supports the existence of a noncollinear antiferromagnetic state. Interestingly, the electric polarization of this sample can be suppressed by a magnetic field. The temperature dependence of the relative magn…
In this paper the structural, magnetic, and dielectric properties of langasite compound Pb$_3$TeMn$_3$P$_2$O$_{14}$ have been investigated as a candidate of short-range magnetic correlations driven development of dielectric anomaly above N$\acute{e}$el temperature of ($T_N$=) 7 K. Presence of dielectric anomaly, structural phase transition and a short range magnetic correlation at the same temperature (at around 100 K) as well as magnetic field dependent capacitance clearly indicate that this compound shows magnetodielectric coupling at around 100 K. In addition, unusual behaviour is observed …
The Haldane spin-chain compound, Tb2BaNiO5, has been known to order antiferromagnetically below (T_N= ) 63 K. The present magnetic studies on the polycrystals bring out that there is another magnetic transition at a lower temperature (T_2= ) 25 K, with a pronounced magnetic-field induced metamagnetic and metaelectric behavior. Multiferroic features are found below T_2 only, and not at T_N. The most intriguing observation is that the observed change of dielectric constant is intrinsic and largest (e.g., about 18% at 15 K) within this Haldane spin-chain family, R2BaNiO5. Taking into account that…
Antiferromagnetic Bi_{2}Fe_{4}O_{9} (BFO), lightly substituted by cobalt is studied for magnetodielectricity. The substitution causes a substantial decrease in the Neel temperature (T_N) from 250 K (in parent sample, BFO) to 152 K (in 2% Co substituted sample). At the same time, the substituted samples display a pronounced irreversibility in the ZFC-FC magnetization data for T $<$ 370 K and opening of hysteresis in the M-H plot, thus signifying the onset of weak ferromagnetism (FM) and magnetic glassiness. The induced magnetic glassiness is found to slow down the dynamics such that the magneti…
The strong coupling between spin, lattice and electronic degrees of freedom in magnetic materials can produce interesting phenomena, including multiferroic and magnetodielectric (MD) behavior, and exotic coupled excitations, such as electromagnons. We present a temperature- and magnetic-field-dependent inelastic light (Raman) scattering study that reveals the emergence of vibronic modes, i.e., coupled vibrational and crystal-electric-field (CEF) electronic excitations, in the unconventional rare-earth MD material, $\text{Ce}_2\text{O}_3$. The energies and intensities of these emergent vibronic…
Magnetoelectric materials have generated wide technological and scientific interest because of the rich phenomena these materials exhibit, including the coexistence of magnetic and ferroelectric orders, magnetodielectric behavior, and exotic hybrid excitations such as electromagnons. The multiferroic spinel material, CoCr$_2$O$_4$, is a particularly interesting example of a multiferroic material, because evidence for magnetoelectric behavior in the ferrimagnetic phase seems to conflict with traditional noncollinear-spin-driven mechanisms for inducing a macroscopic polarization. This paper repo…
Magnetodielectric materials are characterized by a strong coupling of magnetic and dielectric properties and in rare cases simultaneously exhibit both, magnetic and polar order. Among other multiferroics, TbMnO3 and GdMnO3 reveal a strong magneto-dielectric (ME) coupling and as a consequence fundamentally new spin excitations exist: Electro-active magnons, or electromagnons, i. e. spin waves which can be excited by ac electric fields. Here we show that these excitations appear in the phase with an incommensurate (IC) magnetic structure of the manganese spins. In external magnetic fields this I…
The dielectric properties of Fe$_{3}$O$_{4}$ magnetic nanoparticles with an insulating coating layer of SiO$_{2}$ were investigated. At high temperatures, the changes of the dielectric constant and loss induced by the magnetic field are opposite in sign and strongly frequency-dependent, which originates from extrinsic magnetodielectric coupling-the Maxwell-Wagner effect combined with magnetoresistance. And the interface defects leads to the obvious hysteresis phenomena observed in the measurements. On the other hand, the strong coupling of dielectric and magnetic properties at low temperatures…
Ferroelectricity in the incommensurate helical magnetic phase (below TN, 43K) of alpha CaCr2O4 has been confirmed by pyroelectric measurements. Magnetoelectric and magnetodielectric coupling exist below TN and are proportional to the square of magnetic field. From symmetry analysis, we suggest that the presence of an external electric field destabilizes the symmetrical 2221' phase and stabilizes 21' symmetry. This provides a unique system in which polarization varies as the fourth-degree of the order-parameter amplitude and exhibit a vanishingly small value below the first-order transition at …
GaFeO3, AlFeO3 and related oxides are ferrimagnetic exhibiting magnetodielectric effect. There has been no evidence to date for ferroelectricity and hence multiferroicity in these oxides. We have investigated these oxides as well as oxides of the composition Al1-x-yGaxFe1+yO3 (x = 0.2, y = 0.2) for possible ferroelectricity by carrying out pyroelectric measurements. These measurements establish the occurrence of ferroelectricity at low temperatures below the Nèel temperature in these oxides. They also exhibit significant magnetoelectric effect. We have tried to understand the origin of ferroel…
Evidence for reentrant quantum paraelectric state preceded by a multiglass phase with non-classical exponent and magnetodielectric coupling in SrFe12O19
We have carried out dc magnetization (M), heat-capacity (C) and dielectric studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic Pbam structure, in which well-known multiferroics RMn2O5 (R= Rare-earths) form. The points of emphasis are: (i) The magnetic ordering temperature of Cr appears to be suppressed compared to that in isostructural Nd counterpart, NdCrTiO5, for which the Neel temperature is about 21 K. This finding on the Gd compound suggests that Nd 4f orbital plays a role on the magnetism of Cr in contrast to a proposal long ago. (ii) Dielectric constant does not …
The Haldane spin-chain (S=1) insulating compound, Sm2BaNiO5, which has been proposed to order antiferromagnetically around (T_N=) 55 K, was investigated for its complex dielectric permittivity, magnetodielectric and pyrocurrent behavior as a function of temperature (T). In order to enable meaningful discussions, the results of ac and dc magnetizatioin and heat-capacity studies are also reported. We emphasize on the following findings: (i) There is a pyrocurrent peak near T_N, but it is shown not to arise from ferroelectricity, but possibly due to 'thermally stimulated depolarization current', …
We report the evolution of structural, magnetic and dielectric properties due to partial substitution of Ba by Sr in the high temperature multiferroic YBaCuFeO5. This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the YBa1-xSrxCuFeO5 (x = 0.0, 0.25 and 0.5) show that substitution of Sr shifts magnetic transition towards higher temperature whereas dielectric transition to lower temperature. These results points to the fact that magnetic and die…
The research on multiferrocity and magnetoelectric coupling in metal-organic system is rare. Very few hybrid organic-inorganic frameworks (HOIF) exhibit direct magnetoelectric coupling (coupling between spins and dipoles) and also restricted to particular COOH-based system. We show how one can design a hybrid system to obtain such coupling based on the rational design of the organic ligands. The layered phosphonate, MnO3PC6H5.H2O, consisting of perovskite layers stacked with organic phenyl layers, is used as a starting potential candidate. To introduce dipole moment, a closely related metal-ph…
Multiferroics is a class of functional materials that simultaneously exhibit ferroelectricity and ferromagnetism in a single structure. We report here the integration of anti-ferroelectricity and ferromagnetism in a new M-type hexaferrite compound, in which 0.3 Sr ions was substituted by 0.2 La3+ ions in SrFe12O19 so as to keep the charge balance. This doped compound is expressed as a molecular formula of La0.2Sr0.7Fe12O19, which was confirmed by XRD to have the same structure as SrFe12O19 with a lattice contraction of 0.59%. Surprisingly, the doping effect turns La0.2Sr0.7Fe12O19 from ferroel…
The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveal that La rich (BF$_{0.50}$-LF$_{0.50}$)$_{0.50}$-(PT)$_{0.50}$ (BF-LF-PT) has ferroelectric rhombohedral crystal structure with space group \textit{$R3c$} at ambient conditions. The temperature dependence of lattice parameters, tilt angle, calculated polarization $(P_{s})$, volume, and integrated intensity of superlattice and magnetic reflections show an anomaly around 170 K. Impedance spectroscopy, dielectric and ac conductivity measurements were performed in temperature range…
