Magnetodielectric Effect Research Articles

Synthesis and ferroic and multiferroic studies on Bi1-xNdxFe0.99Co0.01O3 compositions

The magnetoelectric materials have been being studied due to the scientific chalenges and the very promissing possibility of applications in electronic devices. BiFeO3 is room temperature single-phase multiferroic material. However there are some issues regarding conductivity and undesired parasitic phases that cause the experimentally reduced electrical polarization and low or no net magnetization in this material. In order to solve these questions we studied the effect of partial replacement of Bi3+ by Nd3+ in the Bi1-xNdxFe0.99Co0.01O3 compositions. X-ray diffraction patterns confirmed single phased rhombohedrally distorted perovskite structure in obtained ceramics. Scanning electron microscopy images reveal that the ceramic grains are almost irregular spheres with a 2 μm in diameter, and samples present equal porosity. With the increasing of the Nd3+ substitution the real part of the dielectric constant increased in almost 10 times but decreases the magnetization. As a consequence, the Bi1-xNdxFe0.99Co0.01O3 ceramics presented an induced magnetoelectric voltage and magnetodielectric effects.

Two-dimensional triangular-lattice Cu(OH)Cl, belloite, as a magnetodielectric system

Quantum spins on a triangular lattice may bring out intriguing and exotic quantum ground states. Here we report a magnetodielectric system of CuOHCl wherein $S=1/2\mathrm{C}{\mathrm{u}}^{2+}$ spins constitute a two-dimensional triangular lattice with the layers weakly coupled via Cl-H-O bonding. Despite strong magnetic interactions, as expected from the relatively high value of ${\ensuremath{\theta}}_{\mathrm{CW}}=\ensuremath{-}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, antiferromagnetic transition occurred at ${T}_{N}=11\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, followed by an uprising turn of the magnetic susceptibility below \ensuremath{\sim}7 K. Neutron-diffraction experiment revealed a coplanar spin structure on the triangular lattice below the ${T}_{N}$, with each spin pointing toward the center of a triangle. Of the three spins on a triangle, two are antiparallel and the third one is angled ${120}^{\ensuremath{\circ}}$ to the antiparallel spins. A concerted effect of geometric frustration in the triangular lattice and superexchange interactions through a zig-zag path via double Cu-O-Cu and double Cu-Cl-Cu bridges counted for this spin arrangement. Further investigation using dielectric constant and heat capacity measurements, as well as a microscopic probe of muon spin rotation, revealed a magnetodielectric effect and the possibility of multiferroic transition at ${T}^{*}\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is suspected to be in close relation to geometric frustration in this triangular lattice. The present paper presents a magnetodielectric system on a two-dimensional triangular lattice with chemical stoichiometry. It can also serve as a rare reference to the hotly debated quantum spin-orbital liquid compound $\mathrm{LiNi}{\mathrm{O}}_{2}$.

Experimental and theoretical interpretation of magnetic ground state of FeMnO3

Magnetic structure of FeMnO3 has been studied using temperature dependent neutron diffraction measurements. The compound exhibits ferrimagnetic structure at room temperature and undergoes another long range antiferromagnetic order below 36 K. The evolution of the magnetic structure is tracked as a function of temperature and compared with the physical property measurements such as magnetization and dielectric constants. Mössbauer spectroscopy measurements at selected temperatures and different magnetic fields exhibit strong influence of the magnetic field on the hyperfine splitting in the magnetically ordered state. Neutron diffraction experiments used for studying the magnetic structure also reveals the presence of a strong magnetically disordered phase in addition to the long range ferrimagnetic phase, leading to magnetic anisotropy in the system. Theoretical calculations were carried out to study ordered and disordered FeMnO3 models by means of Density Functional Theory using PBE0 hybrid functional. The magnetic structure resolved from the refinement of neutron diffraction data is in good agreement with the theoretical model for FeMnO3 model, and the values obtained from the magnetization measurements are in good agreement with the theoretically calculated and experimentally refined magnetic structural model. Dielectric measurements on FeMnO3 exhibits phase transition at two temperatures, firstly around 36 K coinciding with the magnetic ordering temperature, and another around 100 K. The influence of magnetic field does not change these temperatures much, but there is slight change in the dielectric response under the applied magnetic field, which can be attributed to the change in magnetodielectric effect from positive to negative with increase in the temperature. The magnetodielectric study shows the presence of positive and negative magnetodielectric values in this system where the cross over takes placed around the magnetic ordering temperature. From a combined look at the theoretical and experimental work, it can be said that FeMnO3 exhibits complex magnetism with interesting, but tunable physical properties.

Synthesis, Structure, and Physical Properties of the Polar Magnet DyCrWO6.

It has recently been reported that the ordered aeschynite-type polar ( Pna21) magnets RFeWO6 (R = Eu, Tb, Dy, Y) exhibit type II multiferroic properties below TN ∼ 15-18 K. Herein, we report a comprehensive investigation of the isostructural oxide DyCrWO6 and compare the results with those of DyFeWO6. The cation-ordered oxide DyCrWO6 crystallizes in the same polar orthorhombic structure and undergoes antiferromagnetic ordering at TN = 25 K. Contrary to DyFeWO6, only a very weak dielectric anomaly and magnetodielectric effects are observed at the Néel temperature and, more importantly, there is no induced polarization at TN. Furthermore, analysis of the low-temperature neutron diffraction data reveals a collinear arrangement of Cr spins but a noncollinear Dy-spin configuration due to single-ion anisotropy. We suggest that the collinear arrangement of Cr spins may be responsible for the absence of electric polarization in DyCrWO6. A temperature-induced magnetization reversal and magnetocaloric effects are observed at low temperatures.

Electronic and Magnetic Field Dependent Dielectric Properties of Zn0.95Fe0.05O

We report a magneto-dielectric effect in Zn0.95Fe0.05O, which was synthesized by the microwave-assisted combustion method. The x-ray diffraction (XRD) pattern of Zn0.95Fe0.05O shows the shift in peaks towards lower theta values in comparison to the XRD pattern of ZnO. Rietveld analysis of XRD data shows the presence of 99.29% of Zn0.95Fe0.05O along with 0.71% ZnFe2O4 in Fe doped ZnO. Infrared spectroscopic studies show the shift in absorption peak towards lower wavenumber with Fe doping at Zn sites in ZnO. Soft x-ray absorption spectroscopy studies show the mixed valence states of Fe (Fe+2 and Fe+3). Magnetic properties show paramagnetic behaviour of Zn0.95Fe0.05O at room temperature. The magneto-dielectric effect is originated in Zn0.95Fe0.05O due to the decrease in space polarization effect in the presence of Fe+2 at the Zn site in a magnetic field. The dielectric constant er is found to be 4.09 × 105 in 1 Hz and 11.65 in 1 MHz frequency in the absence of a magnetic field for Zn0.95Fe0.05O. The dielectric constant er is found to be 2.88 × 105 in 1 Hz and 10.37 in 1 MHz frequency in the 500 Gauss magnetic field for Zn0.95Fe0.05O. Magnetic field sensitivity is found as ~ 16% in the 15 kG magnetic field and 30 MHz frequency for Zn0.95Fe0.05O.

Lorentz magneto-resonator model and colossal magnetodielectric effect of magnetoelectric heterostructures

In the vicinity of their resonance frequency, magnetoelectric heterostructures, which are laminated magnetostrictive material with a piezoelectric resonator, are highly sensitive to external magnetic field. At room temperature colossal magnetodielectric effect near to 30,000% close to the electromechanical resonance frequency was obtained in a magnetic field of about 400Oe. In this article we present a theoretical model for the magnetoelectric heterostructures based on the Lorentz magneto-resonator model. We show that the colossal magnetodielectric effect is related to the polarization direction of the piezoelectric resonator. When the direction of polarization is parallel to the direction of magnetostriction, the magnetodielectric effect of magnetoelectric heterostructures is much higher than that of the polarization direction perpendicular to the magnetostriction direction. The results of this model are in excellent agreement with experimental data. This modeling environment is found to be extremely useful for understanding how magnetoelectric heterostructures are working in various applications and how to design new magnetic-electric integrated resonant devices.

Effects of morphotropic phase boundary on the electric behavior of Er/Ti co-doped BiFeO3 ceramics

Morphotropic phase boundaries (MPB) consisting of rhombohedral and orthorhombic phases formed within the range of 0.1 ≤ x ≤ 0.15 in Bi1-xErxFe0.97Ti0.03O3 ceramics. Orthorhombic phase transition was verified by the appearance of a new mode at 310 cm−1 in Raman spectra. Bridging phases as intermedia phases of MPB were rare in Bi1-xErxFe0.97Ti0.03O3. Polarization and permittivity improved at MPB. Moreover, impedance spectroscopy revealed additional arcs with a distinct small polaron conduction mechanism. Er3+ ions enhanced magnetic properties and induced a permittivity change at Neel temperature. The magnetodielectric effect resulted in a permittivity change rate of ~1% at 10000 Oe.

Novel multiferroicity in orthorhombic SmCrO3

This paper reports the ferroelectricity in antiferromagnetic SmCrO3 with a reasonably large value of spontaneous electric polarization (70 μC/cm2 mC cm−2 at 50 K) based on the measurement of pyroelectric current. The experimental results showed that the temperature of the onset of polar order was evidently higher (about 220 K) than the Neel temperature (TN =197 K) in the magnetodielectric studies. The calculated magnetodielectric effect (MDE) value was explicitly negative with maximum | MDE | values of about 3.6% around 230 K. The absence of a convincing signature in MDE at antiferromagnetic ordering temperature TN indicated the absence of magnetoelectric coupling around this temperature regime. The results further confirmed that the onset of polar order can be attributed to the structural distortion, rather than the canted noncollinear magnetic structure.

Tutorial: Product properties in multiferroic nanocomposites

The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fibers can be assembled into superstructures with the aid of magnetic and electric fields and characterized for possible use in advanced technologies. Chemical-vapor deposition techniques have been shown to be effective for the preparation of heterostructures of ferrites and ferroelectrics. Exotic planar multiferroic structures with potential for enhancing ME coupling strengths are also considered. Scanning probe microscopy techniques are ideal for probing the nature of direct- and converse-ME coupling in individual nanostructures. Magnetoelectric characterization of assemblies of nanocomposites can be done by ME voltage coefficient, magnetic field induced polarization, and magneto-dielectric effects. We conclude with a brief discussion on possible avenues for strengthening the product properties in the nanocomposites.

Unveiling hidden structural instabilities and magnetodielectric effect in manganese fluoroperovskites AMnF3

Recent theoretical studies predict potential multiferroicity in $AB{\mathrm{F}}_{3}$ fluoroperovskites, challenging their experimental confirmations. Here, we show that magnetic manganese fluoroperovskites ${\mathrm{NaMnF}}_{3}$, ${\mathrm{RbMnF}}_{3}$, and ${\mathrm{CsMnF}}_{3}$ reveal clear evidence of intrinsic lattice instability via the temperature behavior of the dielectric permittivity ${\ensuremath{\varepsilon}}_{0}(T)$. Mechanisms of the instability closely correlate with the geometric tolerance factor $t$ and differ from those in oxide perovskites. In particular, a dramatic 170% growth of the permittivity ${\ensuremath{\varepsilon}}_{0}(T)$ takes place at low temperatures in ${\mathrm{NaMnF}}_{3}$ with the smallest tolerance factor $t=0.78$. Below ${T}_{N}$, this growth is accompanied by a huge magnetodielectric effect of about 25%. These findings allow us to call ${\mathrm{NaMnF}}_{3}$ an incipient multiferroic and open up opportunities for designing multiferroics on the basis of fluorides using chemical and strain engineering.

Asymmetry induced intrinsic magnetodielectric effects in manganite – Barium titanate solid solutions

Multiferroics, in which off-center magnetic ions induced ferroelectricity, are believed to exhibit enhanced magnetoelectric (ME) or magnetodielectric (MD) effects because their ferroelectricity and ferromagnetism are driven by the same originations. In this paper, multiferroics with off-center Mn ions were obtained in hexagonal manganite-barium titanate solid solutions. As an external magnetic field (H) was applied, intermediate and high frequency MD effects were observed. The MD (MD(%) = (ε(H = 3.5 kOe) − ε(H = 0 Oe)) × 100/ε(H = 0 Oe)) values at 10 MHz frequency were 3.37%, 3.21% and 2.65% for the three samples, respectively. The further discussion indicated that the MD effects did not originate from some extrinsic source such as grain boundary magnetoresistance (MR) and contributions from the electrode, but mainly attributed to the intrinsic ME coupling such as magnetic-field-induced variations of asymmetric hopping. The first-principles calculations also confirmed that the asymmetry of coplanar octahedrons aggravated when Mn ions occupied the off-center site in the hexagonal phases, especially in 0.1La0.7Ca0.3MnO3 − 0.9BaTiO3 solid solutions.

Magnetodielectric coupling in a Ru-based 6H-perovskite, Ba3NdRu2O9

A large spin-orbit coupling is a way to control strong magnetodielectric (MD) coupling in a higher d-orbital materials. However reports are rare on such compounds due to often leaky conductive behavior. Here, we demonstrate MD coupling in a Ru-based 6H-perovskite system, Ba3NdRu2O9. The rare-earth ion in a 6H-perovskite makes the system insulating enough to carry out MD investigation. The compound is ferromagnetically ordered below 24 K (TC), followed by another magnetic feature at T~ 17 K (T2). The dielectric constant clearly traces the magnetic ordering, manifesting a peak at the onset of TC, which is suppressed by the application of an external magnetic field (H). The results indicate the presence of MD coupling in this compound, which is further confirmed by the H-dependence of the dielectric constant. Interestingly, a cross-over of the sign of MD coupling is observed at T ~ T2. We conclude that two different mechanism controls the MD coupling which yields positive and negative coupling, respectively. Both mechanisms are competing as a function of temperature and magnetic field. This brings us a step closer to design and control the magnetodielectric effect in 6H-perovskites containing higher d-orbital elements.

Tailored tunneling magneto-dielectric effects in Co–MgF2 granular nanostructures by in-situ insertion of thin MgF2 layers

We report a Co–MgF/MgF heterostructure that comprises periodic layers of super-paramagnetic Co0.23–(MgF)0.77 and thin crystalline MgF, to tailor the frequency response of tunneling magneto-dielectric (TMD) effect. The results indicate that increasing MgF interlayer thickness (t) from 0 to 4 nm causes the position of peak dielectric change (Δε′/ε′0) at a specific frequency fTMD, to shift from 300 to 3 kHz, while also retaining a slight decrease in Δε′/ε′0 from 2.9% to 2.4%. The magnitude of Δε′/ε′0 can be controlled by varying the Co content in the granular layers. Theoretical curve fittings predict that the TMD effect in the heterostructure arises from both the granular layers and interlayers, and a change in inter-granular distance within the interlayers leads to a shift in the position of fTMD. This study may prove helpful for tailoring the magneto-dielectric response of granular nanocomposites to a particular frequency, with potential magnetoelectric applications over a wide frequency range.

Magnetic properties and enhanced magneto-dielectric effects in nanobased Bi2Fe4O9

The magnetic and magnetodielectric (MD) properties of nanobased Bi2Fe4O9 are investigated. 2 μm × 2 μm × 300 nm nano-crystals exhibit an anti-ferromagnetic (AFM) transition at 235 K and a weak ferromagnetism in the temperature range of 10–310 K, shown by the magnetic hysteresis loops. The samples show a large MD effect with Δε/ε being about −13% at 50 K and 0.45 T, as well as an anomaly of MD effect that increases with increasing magnetic field (H). This large MD effect indicates a strong coupling between the magnetic and dielectric properties in Bi2Fe4O9. Our studies provide strong evidence that both the AFM ordering and ferromagnetism contribute to the MD effects.

Multiferroicity in a spin-chain compound, Tb2BaCoO5, with exceptionally large magnetodielectric coupling in polycrystalline form

We report the results of detailed investigations of magnetization, heat-capacity, dielectric, pyrocurrent, and magneto(di)electric measurements on Tb2BaCoO5, belonging to a hitherto unexplored spin-chain cobaltate family, R2BaCoO5 (R = Rare-earths). The magnetic measurements reveal that this compound exhibits an antiferromagnetic transition at (TN=) 18.8 K and there is a spin reorientation beyond 40 kOe below TN. 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 finding which we would like to emphasize is that the observed value of the magneto-dielectric effect beyond the metamagnetic transition field is the largest (close to 55%, below 10 K, for H = ∼100 kOe) ever reported for polycrystals of a compound in the bulk form, thereby offering a hope to find a single-phase polycrystalline compound at room temperature to enable ease of applications.

Magnetodielectric effects in membranes based on magnetorheological bio-suspensions

Controlled release of bio-active components in systems based on magnetorheological suspensions (MRSs) can be achieved by exploiting the magnetodielectric effects aimed at investigating the time dependence of electrical conductivity in the presence of a magnetic field for similar membranes, and where membranes with stable physical properties in time have been manufactured. Here, magnetorheological bio-suspensions (MRBSs) are prepared using a microfiber cloth soaked with carbonyl iron and various concentrations of honey and turmeric powder. Plane capacitors are manufactured having MRSs as dielectric materials. We build and describe an experimental setup for measuring the electrical resistance and the quality factor of the capacitors in a static magnetic field superimposed on an alternating electric field. The measured quantities are then used to obtain the electrical conductivity and dispersion curves of MRSs-based membranes. The results show that the obtained quantities are sensibly influenced by the electric field frequency, magnetic flux density as well as by the ration between honey and turmeric powder concentrations.

Epitaxial growth and observation of the magnetodielectric effect in ferrimagnetic Lu3Fe5O12 films

The fact that a room temperature magnetodielectric effect is obtained in bulk Lu3Fe5O12 provides optimism for practical spintronic applications, but so far the magnetic and magnetodielectric properties of Lu3Fe5O12 film have rarely been studied. In this work, the epitaxial Lu3Fe5O12 films are grown on (1 1 1) Y3Al5O12 substrates by rf magnetron sputtering technique and subsequently annealed in O2 atmosphere. The magnetization and electron spin resonance (ESR) properties of these films are investigated, showing the ferrimagnetic behavior at the measured temperatures. Furthermore, the effect of the preparation procedures on these garnet films are also studied, and it is found that the quality of these epitaxial films are closely dependent on the sputtering and annealing conditions. More interestingly, the room-temperature magnetodielectric effect reaches up to 0.9% with a low magnetic field of 1000 Oe, and 12.5% under 9000 Oe for epitaxial Lu3Fe5O12/(1 1 1) Y3Al5O12 films. These results demonstrate the tunability of magnetic properties in Lu3Fe5O12 films, and furthermore open an alternative route to achieve a high magnetoelectric response and subsequently develop related devices.

Observation of Magnetodielectric Effect in a Dysprosium-Based Single-Molecule Magnet.

Materials that possess coupled magnetic and electric properties are of significant interest because of their potential use in next-generation magnetoelectric devices such as digital information storage. To date, the magnetoelectric materials that have been studied in-depth have been limited mainly to inorganic oxides such as perovskite oxides. Molecular materials are a promising alternative because their magnetic and electric elements can be combined together at the molecular level via relatively simple molecular designs. Here, we report the coupling of magnetic and electric properties through a magnetodielectric (MD) effect in a single-crystal sample, which is constructed from dysprosium(III) single-molecule magnets (SMMs). The MD effect originates from intrinsic spin-lattice coupling of the dysprosium(III) ion within the sample. This is the first observation of the MD effect in a SMM-based material, which could pave the way toward the synthesis of advanced materials that combine distinct magnetic and electric properties using molecular chemistry for use in molecular devices with nanoscale size.

Linear magnetic field dependence of the magnetodielectric effect in eutectic BaTiO3-CoFe2O4 multiferroic material fabricated by containerless processing

To maximize the formation of an anisotropic interface between the magnetostrictive phase and the electrostrictive phase, a eutectic BaTiO3-CoFe2O4 multiferroic material is fabricated by containerless processing. The composites in this process had a fine eutectic structure, especially at a eutectic composition of BaTiO3:CoFe2O4 = 62:38. TEM observations revealed that the (1 0 0) plane of tetragonal BaTiO3 and the (1 0 0) plane of CoFe2O4 were oriented in parallel. In addition to the largest magnetodielectric effect in the eutectic-composition samples, we confirmed the permittivity is controlled linearly by applying a high magnetic field through forced magnetostriction. So far, the peak of the magnetodielectric effect around 0.25 T has been only found in the sintered CoFe2O4 polycrystalline sample. Thus, the containerless processing provides us a route to produce an ideal microstructure without accompanying 90° domain wall process and rotational magnetization process, which enhances the magnetodielectric effect.

Studies on magnetocapacitance, dielectric, ferroelectric, and magnetic properties of microwave sintered (1-x) (Ba0.8Sr0.2TiO3) - x (Co0.9Ni0.1Fe2O4) multiferroic composite

Present paper reports the synthesis of multiferroic composite (1-x) [Ba0.8Sr0.2Ti)O3]-x[Co0.9Ni0.1Fe2O4] were x = 0.1, 0.2, 0.3 and 0.4. Both phases of the composite i.e. ferroelectric (BST) and ferrite (CNFO) are synthesized via hydroxide co-precipitation method followed by microwave sintering technique at 1100 °C. These composites were characterized for their structural, microstructural, dielectric analysis, magnetodielectric (MD) effect and ferroelectric properties. Presence of both the phases ferroelectric (BST) and ferromagnetic (CNFO) are confirmed by the x-ray diffraction and scanning electron microscopic analysis. Maxwell-Wagner type dielectric dispersion is observed in frequency dependent dielectric measurement. Temperature-dependent dielectric properties were measured from 25 °C to 500 °C at various applied frequencies. Ferroelectric behavior in the composites was confirmed by the polarization vs. Electric field analysis. The magnetodielectric effect was studied in the presence of applied magnetic field from 0 to 1 Tesla. Magnetocapacitance (%) increases with increase in the ferrite concentration in the ferroelectric phase. The maximum percentage of magnetocapacitance is observed in 60BST-40CNFO composite which is MC = 30% at the frequency 1 KHz with the applied magnetic field is 1-Tesla. Room temperature magnetic hysteresis loops show an increase in saturation magnetization (Ms) with an increase in ferrite concentration.