Magnetodielectric Effect Research Articles

Deciphering the Structural Characterization, Hirshfeld Surface Analysis, Raman Studies, and Temperature-Dependent Magnetodielectric Properties of BiMn2O5

We investigate the structural, Hirshfeld surface, magnetic, and magnetodielectric properties of BiMn2O5. The sample can be indexed with an orthorhombic phase associated with space group Pbam, with crystallographic parameters a = 7.54946 Å, b = 8.54962 Å and c = 5.753627 Å. The Hirshfeld surface analysis, associated with 2D fingerprint plots, was used to visualize and explore the significant intermolecular interactions in the crystal structure quantitatively. The Raman spectra, measured from 6 to 300 K in a frequency range between 250 and 750 cm−1, exhibit good agreement between the SHELL model calculations and the experimental measurement of the proximity of the phonon frequencies for our sample. Furthermore, magnetic measurements show that BiMn2O5 becomes antiferromagnetic below the Néel temperature (TN)—the temperature above which an antiferromagnetic material becomes paramagnetic (TN = 31 K). The relaxation at intermediate temperatures (200–300 K) can be attributed to the polar jump process at two charge transfer sites between the Mn3+ and Mn4+ ions, which, in combination with the special arrangement of the Mn3+/Mn4+ ions, is likely to produce the strong intrinsic magnetodielectric effect (MD) in the same temperature range.

Electronic band structures of NdFe3(BO3)4 and NdGa3(BO3)4 crystals: ab initio calculations

NdFe3(BO3)4 and NdGa3(BO3)4 crystals are of great interest due to their physical properties. For example, NdFe3(BO3)4 crystal demonstrates magnetodielectric and magnetopiezoelectric effects, and NdGa3(BO3)4 crystal possesses luminescent and nonlinear optical properties. In this work, the properties of these materials are calculated by the plane-wave pseudo-potential method based on density functional theory. The structures of the crystals are optimized. The electronic structure of NdFe3(BO3)4 and NdGa3(BO3)4 are calculated.

Impedance spectroscopy and magneto-dielectric analysis of La3+ substituted Co2Z hexaferrite

Single phase Ba3Co2Fe24O41 (Co2Z) and Ba2.8La0.2Co2Fe24O41 (La-Z) were prepared by solid state ceramic method. The dielectric, impedance and electric modulus were systematically investigated as a function of temperature from 50 °C–250 °C and in the frequency range of 1 Hz–1 MHz. Frequency dependent imaginary impedance and electric modulus implies that La3+ substitution significantly affect hopping and relaxation mechanism of charge carriers. Cole-Cole plots (Z" vs Z') has been fitted with suitable equivalent circuit for both Co2Z & La-Z. The obtained grain and grain boundary resistances confirmed that charge carriers experienced lower resistance in La-Z. Arrhenius plots of relaxation time (τ) vs 1/T showed parallel conduction mechanism in system. Complex electric modulus spectrum distinguished the capacitive contribution of grain, grain boundary and electric effect. A very high magnetodielectric effect at low frequencies has been observed for La-Z.

High temperature spin-driven multiferroicity in ludwigite chromocuprate Cu2CrBO5

We report spin-driven multiferroicity above 100 K in the ludwigite Cu(II) oxyborate Cu2CrBO5. Spontaneous polarization, which reaches 35 μC m−2 at 5 K, appears below 120 K, concomitantly with an incommensurate antiferromagnetic order and complex magnetodielectric effects. In magnetically induced ferroelectrics, multiferroicity usually appears at low temperature because of the competing magnetic exchanges needed to stabilize a magnetic spiral. The remarkably high transition temperature observed in Cu2CrBO5 originates from the presence of strong Cu–O–Cu magnetic super-exchange interactions, which are not weakened by Cu/Cr cationic disorder. Our result provides an important contribution to the search for high temperature spin-driven multiferroics among low-dimensional cuprates.

Probing magnetic symmetry in antiferromagnetic Fe4Nb2O9 single crystals by linear magnetoelectric tensor

In the present study, we investigated magnetodielectric, magnetoelectric (ME), and angular-dependent polarization in single-crystal Fe4Nb2O9. The magnetodielectric effects in epsilon(x) (x//[100]), epsilon(y) (y//[120]), and epsilon(z) (z//[001]) are found to be significant only around T-N approximate to 95 K when magnetic fields are applied along three orthogonal x-, y- (y//[120]), and z directions. The finite polarization P-x, P-y, and P-z of 70, 100, and 30 mu C/m(2), respectively, can be induced in the antiferromagnetic phase when a finite magnetic field up to 9 T is applied along the three orthogonal directions. The angular-dependent polarization measurements verify the dominating linear ME effects below T-N. From the above experimental results, a linear ME tensor a(ij) with all nine nonzero components can be inferred, demonstrating a much lower magnetic point group of -1' for the canted antiferromagnetic configuration.

Anisotropic spin-driven ferroelectricity and magnetoelectric effect in a Y-type hexaferrite

We report a systematic study on the magnetic, dielectric, and magnetoelectric (ME) properties of the Y-type hexaferrite (Ba0.4Sr1.6)Zn2(Fe11.3Al0.7)O22 single crystal. The phase diagrams were established by the observed magnetic anomalies under magnetic field and temperature scans for the in-plane and out-of-plane cases. Intrinsic large anisotropy in the magnetodielectric and converse ME effects was revealed. The spin-driven electric polarizations induced in the ab-plane and out-of-plane were found to be closely related to the transverse conical and alternating longitudinal conical spin structures, respectively. The amplitudes of varied magnetization ΔM are about ∼0.128 μB/f.u and ∼0.0178 μB/f.u. in the E oscillating between ±1 MV/m at 100 K, corresponding to the converse ME effect coefficient of ∼3500 ps/m and ∼480 ps/m for the in-plane and out-of-plane cases, respectively. All these results demonstrate the essential and unique spin-order-induced anisotropic ferroelectricity and ME properties in these Y-type hexaferrites.

Magnetodielectric effect in ceramics based on PbFe1/2Nb1/2O3

The results of X-ray diffraction analysis of solid solutions (SS) of the system (1−x)Pb(Fe1/2Nb1/2)O3–xPb(Fe2/3W1/3)O3 with x = 0.0 ÷ 0.8, study of their microstructure and measurements of magnetodielectric characteristics are presented in this work. It is shown that all obtained SS have a perovskite-type structure without extraneous phases. The critical influence of the resulting liquid phase on the sintering process and microstructure of SS is established. A magnetodielectric effect in all the SS is detected. The shift on the temperature dependences of dielectric spectra of SS to a higher temperature region under the effect of a magnetic field is revealed.

High-resolution magnetic sensors in ferrite/piezoelectric heterostructure with giant magnetodielectric effect at zero bias field

A dielectric AC magnetic sensor in layered ferrites/piezoelectric composites was fabricated and developed, whereby its high magnetodielectric (MDE) effects, the typical magnetic-sensing parameters, were systematically characterized at zero bias. Polycrystalline ferrites were synthesized by the solid-state sintering technique with a composition of Ni0.7Zn0.3Tb0.02Fe1.98O4, and the desired spinel structure and soft magnetic properties were confirmed by x-ray diffraction and VSM, respectively. The field-induced charge order insulating state in piezoelectric ceramics accounts for the suppressed permittivity, which enables the possibility of a highly sensitive magnetic sensor at zero bias field. Experimental results exhibit that a small variation in H as low as 100 mOe can be clearly distinguished with a favorable nonlinearity of 2.24%. Meanwhile, the output stability of the presented sensor under 2h of constant and continuous excitation was tested within a favorable fluctuating tolerance range of 6.14-6.28 nF, and the estimated uncertainty of ∼0.063 038 nF was verified by statistical analysis. The presented ferrite/piezoelectric magnetic sensors exhibiting a high MDE response without the requirement for an external magnetic bias are of importance for use in bio-magnetic field detection due to metrics of miniaturization, high sensitivity, and favorable stabilities.

Remarkable effects of dopant valency – a comparative study of CaBaCo3.96Cr0.04O7 and CaBaCo3.96Ni0.04O7

Distinctive effects of dopant valency is discussed using an impurity level 1% doping each of Cr3+ and Ni2+ in CaBaCo4O7. Through a comparative study of the magnetic and dielectric properties of magnetoelectric CaBaCo3.96Cr0.04O7 and CaBaCo3.96Ni0.04O7, we highlight that Cr doping does not significantly alter the properties in spite of differences in magnetic spin and ionic radius compared to Co3+ and Co2+ while Ni doping induces spectacular changes. Particularly, about 4 times larger electric polarization change (~650 μC/m2 at 5.6 kV/cm) is observed in CaBaCo3.96Ni0.04O7 compared to CaBaCo3.96Cr0.04O7 and a stronger magnetoelectric coupling leading to a polarization change of ~12% in 15 T magnetic field, below 40 K. Further, magnetodielectric effects hint to competing magnetic phases over the temperature range of magnetic transitions. The article discusses the observed disparity in the light of a possible site selective doping of Cr3+ and Ni2+ in the triangular and kagomé layers, respectively, of the parent compound.

Magnetodielectric Response in a Layered Mixed-Valence Ferrimagnetic Molecular Compound.

The magnetodielectric effect is closely related to multiferroic or magnetoelectric coupling; thus, it can be used to predict magnetoelectric coupling, especially in compounds with special magnetic properties. The magnetodielectric response can often be used to predict many interesting and meaningful physical coupling mechanisms. Therefore, fabricating magnetodielectric materials is an effective step toward the development of magnetoelectric materials. Herein, we synthesize the mixed-valence layered ferrimagnetic molecular compound (C6N2H14)FeIII2FeIIF8(HCOO)2 (1) and demonstrate that it exhibits both slow magnetic relaxation behavior and long-range magnetic order. This long-range order occurs because of the coexistence and competition between two typical magnetic interactions, namely, an FeIII-F-FeII superexchange and a long-distance superexchange FeII-O-C-O-FeIII-F-FeIII path in the interlayer and interchain spin frustration. Notably, this compound also demonstrates two abnormal dielectric relaxation processes: the first process is dominated by dynamic guest cations, while the other process is related to the increasing magnetic correlation. Over a wide temperature range below 170 K, the magnetodielectric effect reveals that the magnetic correlation maybe promotes electron dynamics and leads to magnetodielectric coupling. These findings pave a novel path for designing magnetodielectric molecular materials.

Exotic magnetic behavior with intrinsic and extrinsic magnetodielectric effects in Pr2CuMnO6

We present a systematic exploration of structural, electrical transport, thermomagnetic, and magneto–dielectric properties of polycrystalline perovskite, Pr2CuMnO6. Powder X-ray diffraction confirms the orthorhombic crystal structure with the Pbnm space group. The electrical transport studies reveal high resistivity (1.34 ×104 ohm–meter at 123 K) of the compound with semiconducting type temperature variation, and the conduction process follows the variable range hopping of polarons. Magnetization measurements reveal the magnetic ordering at 55 K followed by a cluster glass phase below 22 K. Frozen magnetic phase at lower temperature results from competing short-range FM/AFM interactions due to atomically disordered mixed valent B-site ions (Cu2+/3+ and Mn3+/4+). Inverse DC susceptibility reveals the observation of Griffiths phase above the glassy transition, extending up to 66 K. Magnetodielectric (MD) analysis reveals intrinsic MD effect (20 – 100 K) due to spin-lattice coupling followed by extrinsic MD effect (100 – 180 K) due to Maxwell–Wagner contribution.

Composition-graded multilayer nanogranular films enabling broadband tunneling magneto-dielectric effect: Role of the granular distribution

The tunneling magneto-dielectric (TMD) effect, which causes a magnetic field-induced increase in the dielectric permittivity (ε′0) of nanogranular films, is promising for use in multifunctional devices. However, the frequency response of the TMD effect features a peak dielectric change (the TMD ratio, Δε′/ε′0) at a specific frequency, which inevitably limits the utility of the effect to within a narrow frequency range. To achieve the high TMD effect over a wider frequency band, we experimentally and theoretically report composition-graded multilayer (CGM) Co-MgF2 nanogranular films (i.e., with a step-varied granular Co content) with still high TMD ratios beyond this particular frequency range. Theoretical fittings of the experimental dielectric and TMD results indicate that the wide inter-granular spacing distribution in CGM films represents the origin of the broadband TMD effect. This study clarifies the critical role of the granular distribution in regulating the frequency response of the TMD properties. The proposed CGM structure, which can go beyond the limitations of conventional uniform nanogranular materials, will enable broadband magnetoelectric device applications of the TMD effect.

Electric, dielectric and magnetic properties of Ga, Er and Zn ion doped Fe2O3 thin films

Using a microscopic model we have investigated the electric, dielectric and magnetic properties of Ga, Er and Zn doped α-Fe2O3 thin films. The polarization P in Ga doped α-Fe2O3 decreases with increasing Ga content x, and increases with enhancing magnetic field h and decreasing film thickness N. In Ga doped hematite the dielectric constant ϵ shows a peak at TC. ϵ decreases with increasing h, indicating a strong magneto-dielectric effect. The contributions of the spin-phonon and phonon-phonon interactions below and above TC are considered. The dielectric constant in Ga, Er and Zn ion doped Fe2O3 can increase or decrease for different ions and different ion doping concentration. The ion doping dependence of the magnetization is also calculated.

Magnetic Properties and Magnetodielectric Effect in (C6H5CH2NH3)2[CuCl4] with Organic-Inorganic Hybrid Layered Structure

Metal Organic Frameworks (MOFs) are a group of multiferroic candidates that exhibit various optical, electrical, magnetic, and structural properties depending on the type of organic cations, transition metals and halogen elements, and their molar ratio. (C6H5CH2NH3)2[CuCl4] (BZACC), one of the MOF materials, has a special hybrid layered structure of organic and inorganic layers. Magnetic property measurement showed that BZACC exhibits weak in-plane ferromagnetism below the Curie point (TC) of 10.25 K and the saturated magnetic moment of 1 µB per formula unit at 2 K. When the magnetic field is less than 0.1 T along the c axis, it exhibits weak antiferromagnetism below 8 K. From the measurement of the dielectric constant with external magnetic field, we observed a maximum magnetodielectric (MD) effect of 0.4% at 2 K. Furthermore, it was found that the magnetic-field dependence of the MD effect is similar to that of the second derivative of magnetization with respect to magnetic field. We suggest that the observed MD effect is the consequence of the magnetic-field-induced spin structure change in the inorganic layer, which induces the change in the interlayer magnetic coupling and, as a result, induces the change in the dielectric constant by the applied magnetic field.

Effect of Ca dopant on magnetic and magnetodielectric properties of Y3Fe5O12

A series of Ca-doped yttrium iron garnet ceramics (Y3-xCaxFe5O12 (x = 0, 0.05, 0.1, 0.15, 0.2)) were prepared by the solid state method. The structure, morphology, valence fluctuation, thermal analysis, magnetization, magnetodielectric and Mössbauer spectrum of Y3-xCaxFe5O12 ceramics were systematically studied. All of the samples crystalized as single phase of garnet structure with the grain sizes of 2–3 μm. The temperature dependent percentage weight loss and heat flow were investigated by thermogravimetric (TG) and differential scanning caborimetry (DSC). The structure of Y3-xCaxFe5O12 ceramics was studied by XRD, Raman and Infrared (IR) spectra. The results indicated that Ca2+ substitution leads to lattice expansion and presence of Ca–O octahedron, which causes the concentration of Fe2+ decrease and Fe4+ increase. As a result, the saturation magnetization first increases and then decreases with the increase of Ca concentration. A six lines asymmetry of magnetic components were observed in Mössbauer spectrum, which was fitted by two hyperfine magnetic sextets corresponding to tetrahedral and octahedral sites, respectively. With the increase of Ca concentration, the intrinsic magnetodielectric (MD) effect disappears completely due to the dramatic decrease of Fe2+-Fe3+ dipoles. Fe3+-Fe4+ dipoles do not contribute to the MD properties of Y3-xCaxFe5O12 ceramics due to the lack of the defects such as electrons or holes being used as media.

Lattice dynamics and spontaneous magnetodielectric effect in ilmenite CoTiO3

Ilmenite-type crystals find a variety of technological applications due to their intriguing physical properties. We present the results of the lattice dynamics studies of honeycomb antiferromagnetic ilmenite CoTiO3 single crystal by the complementary polarized infrared, Raman, and dielectric spectroscopic techniques that are supplemented by the DFT calculations. The symmetries and frequencies of all predicted infrared- and Raman-active phonons were uniquely identified. Furthermore, it was found that the dielectric permittivity demonstrates distinct changes below antiferromagnetic ordering temperature in zero magnetic field due to the spontaneous magnetodielectric effect. Our results establish the solid basis for further investigations and more deep understanding of the coupling of phonons with spins and magnetic excitations, as well as their involvement in other physical phenomena in this promising material.

Multiple dielectric relaxations and superior sonocatalysis of bismuth iron niobate pyrochlores via high-level Co-doping

Manipulating the structure of Bi-based pyrochlores can produce excellent physicochemical properties and novel phenomena due to lattice disorders and distortions. Herein, bismuth iron niobate pyrochlores via high-level Co-doping were successfully fabricated by a sol-gel auto-combustion method and the doping effects on their structural, magnetic, dielectric and sonocatalytic properties were systematically investigated. Rietveld refinements revealed substituting Fe sites with Co ions (at a ratio of 30%–80%) can maintain the pyrochlore phase and induce larger lattice distortion. New dielectric relaxation and outstanding magneto-dielectric effect with a maximal 4% coefficient were clearly observed in the heavily Co-doped sample at low temperatures, which correlate with structural disorder and magnetic state transitions. New types of dielectric anomalies that gradually change the relative permittivity but maintain the dielectric loss almost constant with increasing temperature or frequency and can be tuneable at different doping levels were first observed above room temperature. The activation of ultrasonic vibration-driven degradation in the specimens was evaluated by the catalytic oxidation of dye, and the Fe/Co-coexisting catalysts exhibited superior sonocatalytic activity with magnetic recyclability, opening up a new pathway of developing feature-rich pyrochlores in the catalytic field.

Magnetodielectric coupling tuning through domain wall charge accumulation in co-doped BiFeO3 with Sr2+ and Mn3+

We report the effect of Sr2+ and Mn3+ co-doping BiFeO3 on the crystal structure and the multiferroic properties of Bi0.95Sr0.05Fe1-xMnxO3 (0.0 = x ≤ 0.4, Δx = 0.1) powders, synthesized by assisted high-energy ball milling of stoichiometric mixtures of Bi2O3, Fe2O3, SrO, and Mn2O3; the powders were pressed at 900 MPa and sintered at 800 °C. X-ray diffraction and Rietveld refinement reveal the effect of Sr2+ and Mn3+ on the crystal structure. These elements act as inhibitors of secondary phases. Magnetic behavior, obtained using vibrating sample magnetometry shows antiferromagnetic order and an increase in magnetic susceptibility, due to slight differences in ionic radii and low crystal structure distortion. All the samples show high relative permittivity values, which is augmented by doping with Sr2+ and Mn3+ ions furthermore, the doping increases dielectric dissipation factor; it is attributed to their interaction with different oxidation state cations like Fe3+, Fe2+, Mn3+, Mn2+, Bi3+, and Sr2+, into the crystal structure of BiFeO3. Additionally, it was found increments of the electrical conductivity, due to the domain-wall charge accumulation phenomenon. In the same way, the relative permittivity improves as an effect of domain-walls conductivity, induced by Sr and Mn co-doping. The magnetodielectric effect presents a change in mechanism origin, from core-dominated (grain) to interface-dominated (electrode-dielectric, and grain-grain boundary), as a result of domain-wall charge accumulation.

Large magnetodielectric effect based on spin-dependent charge transfer in metal–insulator type Co-(BaF2) nanogranular films

Cobalt-metal-fluoride nanogranular films exhibit high electrical resistivity (ρ) and high permittivity (ɛ′) as well as high magnetic moments, making them potentially suitable for applications in low power magnetoelectronic devices at a high-frequency range. Here, we present the DC/AC magnetoelectric effect of high-ρ Cox-(BaF2)1 − x nanogranular films that are constituted of Co nanogranules of about 2 nm in diameter in an insulating BaF2 crystal. Under the application of magnetic field (H), we observed the ρ variations (Δρ/ρ0) of 2.0%–5.9% for x ranging 0.19–0.54 and the ɛ′ variations (Δɛ/ε0′) of 0.7%–6.0% for x ranging 0.19–0.42, respectively. These magnetically controllable ρ and ɛ′ are realized based on the spin-dependent quantum-mechanical charge transfer. The Cox-(BaF2)1 − x film for x = 0.42 possesses high ρ, while remaining in a notably high Δɛ/ε0′ of 6% at a megahertz frequency range. This study demonstrates a candidate of high-resistive magnetoelectric nanogranular films, which may bring prosperous applications in high-frequency magnetoelectric devices with low power consumption.

Magnetodielectric effect and spin state of iron ions in iron-substituted bismuth pyrostannate

The magnetic and magnetodielectric properties of bismuth pyrostannate $$\hbox {Bi}_{{2}}(\hbox {Sn}_{1-{x}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ ( $$x = 0.1$$ and 0.2) have been examined. Using the Mossbauer spectroscopy and electron paramagnetic resonance, the high-spin state and crystallographic positions of iron ions have been established. The coexistence of triclinic symmetry domains in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}(x = 0.1)$$ compound with the monoclinic symmetry below 140 K has been found. For the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ composition with $$x = 0.2$$ , the nonlinear field dependence of magnetization in the paramagnetic region up to room temperatures has been observed. The electric polarization hysteresis and the magnetoelectric effect in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ compound have been disclosed. The magnetic field-dependent anomalous behavior of magnetization has been explained by the magnetoelectric effect.