Magnetoelectric Properties Research Articles

Positional-Fe-doping-induced spin polarization effects on magnetoelectric properties and spin texture of 2D-SiC

Abstract The electronic structure and magnetic properties of positional-Fe-doped 2D-SiC were systematically studied using the first-principles plane wave pseudopotential based on the generalized gradient approximation(GGA) +U scheme. We found that d electrons with small-polaron behavior acted as itinerate conductive particles in the electron band structure of Fe-substituted Si-doped system, leading to its magnetic anisotropy. Additionally, the spin-up of Fe-d electrons was split as a result of the crystal field effect. The t2g and eg electron levels were risen, while the dz2 levels were lowered, as a deep impurity level was observed at −0.24 eV lower than the nearest d-orbital level. The spin texture of the doped matrix demonstrated that both Rashba–Dresselhaus-type SOC coexist in the polar system. Rashba–Dresselhaus SOC mainly induced the interaction between spin and charge, motivated the spin pumping in the polar matrix. These results confirmed that Fe-doped 2D-SiC is a potential next-generation spintronics material.

Enhancement in magnetoelectric properties of lead-free multiferroic composite through high-energy mechanical milling

Ferrite-Ferroelectric composites with the generic formula y(Mn0.5Cu0.5Fe2O4)1 − y[Ca0.1Ba0.9Zr0.1Ti0.9] (y = 25%, 50% and 75%) are prepared by solid-state reaction. One of the prepared samples of the composites 25%Mn0.5Cu0.5Fe2O4–75%Ca0.1Ba0.9Zr0.1Ti0.9O3 (MCF-CBZT) is subjected to high-energy mechanical milling for different durations (12 h, 18 h and 30 h). The compositional stoichiometry of all the samples is checked by Energy Dispersive Spectroscopy. All the un-milled and milled samples are characterized by X-ray diffraction, scanning electron microscopy, FTIR, magnetometry, and dielectric and magnetoelectric coefficient measurements. Magnetoelectric composite possesses biphasic surrounding to exhibit complex behavior of ME effect. The present study reveals influence of mechanical milling on MCF-CBZT magnetoelectric composite. The XRD confirms the presence of ferrite and ferroelectric phases for all the samples and microstructural changes appear in SEM images of milled specimens. FTIR spectra show four characteristic bands in 400–800 cm−1 range. Saturation magnetization and Curie temperature decrease as milling duration increases. Relaxed broad doublet with the distribution of nuclear hyperfine fields is found in Mossbauer spectra indicating good coupling between ferrite-ferroelectric phases caused by mechanical milling for the multiferroic composite. The frequency response of dielectric constant and loss tangent is recorded in the frequency range from 100 Hz to 1 MHz. The static value of magnetoelectric factor has been studied as a function of magnetic field for un-milled and milled MCF-CBZT samples. The maximum value 382 μV/cm·Oe of (ME)H is observed for the 18 h milled MCF-CBZT sample.

Enhancement of magnetoelectric coupling in Cr doped Mn2O3

The effect of Cr doping has been undertaken to investigate its effect on the structural, magnetic, dielectric and magnetoelectric properties of newly discovered multiferroics material α-Mn2O3. The Cr doping modifies the room temperature crystal symmetry i.e. transforms from orthorhombic to cubic symmetry. Similar to α-Mn2O3, two magnetic transitions have been observed in all Cr doped samples. The effect of Cr doping manifested on the low temperature transition. The lower magnetic transition shifted toward higher temperature (25 K for pristine to 40 K for Cr = 10%) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in temperature dependent complex dielectric measurements for Mn2−xCrxO3 (0 ⩽ x ⩽ 0.10) samples around high temperature magnetic ordering ∼80 K which corroborate the magnetoelectric coupling in these samples. Interestingly, the magnetodielectric value enhanced significantly with Cr doping and a maximum increase of ∼21% is observed for 10% Cr doped sample at 5 K around 70 kOe magnetic field.

Magneto-electric coupling and transport properties of LaFeO3–Pb(Zr0.58Ti0.42)O3–organic poly(vinylidene fluoride) nanocomposite

The magneto-electric material of LaFeO3–Pb(Zr0.58Ti0.42)O–poly(vinylidene fluoride) has been prepared by a chemical “pyrophoric reaction technique” and followed by “solid state route”. The formation of LaFeO3, Pb(Zr0.58Ti0.42)O3 and poly(vinylidene fluoride) phases is confirmed by X-ray diffraction technique. The magneto-electric coupling and electrical response have been carried out at room temperature (300 K). The prepared composite reveals the strain mediated magnetoelectric effect at room temperature with longitudinal and transverse configurations at lower frequency region under an external magnetic field. The impedance spectroscopy is used to study the complex electrical modulus and electrical transport properties of the prepared composites at room temperature. The complex modulus and impedance spectra study also helps to understand the mechanism of the electrical transport process, which depicts a non-Debye type of conduction mechanism of the system.

Magnetoelectric Properties of Co1−xNixFe2O4/BaTiO3 Heterostructures with 3–3 Connectivity Obtained by Eutectic Crystallization

Multiferroic composites consisting of 62 mol% ferroelectric Ba0.97Sr0.03TiO3 and 38 mol% ferrimagnetic Co1–xNixFe2O4 with Ni substitution levels of x = 0, 0.25, 0.50, 0.75, and 1.00 are obtained from eutectic crystallization in a floating zone furnace. Scanning electron microscopy reveals the self‐organized formation of a 3–3 network. Epitaxy of the two phases is confirmed by single‐crystal X‐ray diffraction. All samples, except the one containing pure NiFe2O4, are free of impurity phases. The influence of the substitution level x on the unit cell parameters of both materials is investigated by Rietveld refinement before and after a reoxidation process in flowing oxygen at 1173 K. The amount of oxide defects is determined by thermal analysis, showing a nearly constant value throughout the whole Co1–xNixFe2O4 series. The effect of Ni substitution on the magnetic properties (saturation magnetization and magnetic transition temperature) of the eutectics is investigated. The magnetoelectric (ME) properties of the samples are studied in dependence on the DC field (HDC), the frequency of the AC field (HAC), and temperature. The Ni content has a strong influence on the absolute value of the ME coefficient (αME), but only a slight effect on the general behavior of the ME properties.

Structural transformation induced enhanced multiferroicity in Al3+ and Ti4+ co-doped LaFeO3

In order to enhance the magnetoelectric property of LaFeO3, we have considered co-substitution of Al3+ and Ti4+ in La3+ and Fe3+ sites. Rietveld refinement of the observed XRD patterns confirms that the pristine (LaFeO3, LFO) crystallizes in orthorhombic Pbnm (centrosymmetric) space group whereas the doped samples (La0.9Al0.1Fe0.9Ti0.1O3, LAFTO) crystallizes in orthorhombic Pna21 (non-centrosymmetric) space group due to co-doping of Al3+- Ti4+ in LFO. Analysis of magnetic data confirms the antiferromagnetic phase of LFO and LAFTO possess ferrimagnetic spin structure with enhanced magnetization. Besides this ferroelectric polarization at room temperature is also improved in the co-doped sample of LAFTO (Pmax = 0.25 µC/cm2). Spontaneous polarization is predicted from first principle calculation for LAFTO to be ~ 12.31 µC/cm2. The dielectric loss factor of LAFTO reduces significantly and the dielectric strength is also enhanced compared to that of LFO. Experimental results are in agreement with these findings extracted from ab initio calculations using density functional theory. The present doped sample LAFTO has improved magnetic, dielectric, ferroelectric properties and magnetoelectric coupling compared to that of LFO, would have the high potential for applications in multiferroic devices.

Dielectric response and magneto-electric interaction of La1.67Sr0.33NiO4 single crystal

The dielectric response of La1.67Sr0.33NiO4 single crystal varies with the frequency, temperature and magnetic field has been investigated. Experimental results show that the dielectric constant reaches 104 at high temperature region, and the low temperature dielectric behavior confirms that the electrical transport behavior follows a variable-range-hopping (VRH) model. The dielectric behavior varies with the external magnetic field where the magnetic field induced phase transition of charge order (CO) is companied with the change of the dielectric behavior, indicating a magnetoelectric properties of the charge ordered compound of La1.67Sr0.33NiO4. Therefore, the coexistence of Ni3+ and Ni2+ ions makes the CO, which responds orderly at high temperature under the action of external magnetic field may contributed to the observed magnetodielectric behavior.

Magnetic Domain-Wall Induced Electric Polarization in NdCrO3 Polycrystalline Ceramic.

We reported the magnetic, dielectric and magnetoelectric properties of NdCrO3 polycrystalline ceramics. Magnetization curves revealed two magnetic transitions at 227 K and 38 K, which corresponded to Cr3+ canted antiferromagnetic ordering and Cr3+ spin reorientation phase transition, respectively. At 11.5 K, a Schottky-type anomaly was observed, caused by Nd3+ ground doublet Zeeman splitting. High-temperature dielectric relaxation exhibited a type of thermally activated relaxation process, which mainly resulted from the Maxwell–Wagner effect. The spin-reorientation of Cr3+ ions and the Nd3+ ground doublet splitting were observed to be accompanied by an electric polarization. The polarization could be induced by the presence of the antiferromagnetic-type domain walls, which led to spatial inversion symmetry breaking.

Multiferroic polymer composite based on Heusler-type magnetic microwires with combined magnetocaloric and magnetoelectric effects

We have studied the magnetocaloric and magnetoelectric properties of a new type of the magnetoelectric composite that consisted of Heusler-type magnetic microwires embedded in a polyvinylidene fluoride piezoelectric polymer matrix fabricated using a modified solvent casting technique. The maximum of the adiabatic temperature change ΔT of ~ 0.04 K was observed around 276 K with narrow hysteresis accompanied with a maximum of magnetoelectric effect. Observed temperature dependences of the magnetocaloric and magnetoelectric effects can be associated with magnetic (paramagnetic-ferromagnetic) phase transition. The measurements of the magnetocaloric effect in modes with different frequencies (0.5–20 Hz) of the modulated magnetic field exhibit a reduction of ΔT about 38%.

Born effective charges and electric polarization in bulk ε-Fe2O3: An ab-initio approach

Limitation in the synthesis of single-crystal has restricted the complete understanding of the magnetoelectric properties of bulk ε-Fe2O3. In order to understand the electric polarization of bulk ε-Fe2O3, we have employed a first-principles Berry-phase method and the density functional perturbation theory to calculate the spontaneous electric polarization and Born effective charges (BECs) of ε-Fe2O3. The polarization quanta of the ferroelectric bulk ε-Fe2O3 and its polarization lattice are also reported. The polarization switching through a paraelectric transition phase of a low barrier is found to be favorable. The polarization and BECs calculated by both methods are in good agreement.

Structural, morphological and magnetoelectric properties of (Bi0.6Ni0.2Ba0.2)(Fe0.6Ti0.4)O3 electronic material

In this work, (Bi0.6Ni0.2Ba0.2)(Fe0.6Ti0.4)O3 magnetoelectric composite has been synthesized using conventional solid state reaction procedure. Form its powder x-ray diffraction investigation the orthorhombic crystal system has been identified. The micrograph shows unique grain growth with different size and shapes. With the help of ferroelectric hysteresis, magnetic hysteresis and magneto electric coefficient has been deliberated. From the ferroelectric hysteresis (P-E loop) the obtained saturation polarization (PS) and remnant polarization (Pr) values are 5.90 µc/cm2 and 1.14 µc/cm2 respectively. From the magnetic hysteresis (M-E Loop) the obtained magnetization saturation (MS) and remnant polarization (Mr) values are 5.45 emu/gm and 1.23 emu/gm respectively. A magnetoelectric coupling coefficient of 55 mv/cm.Oe has been obtained using ME coefficient measurement setup. These studied properties can be useful for developing magnetic and electric field sensor applications.

Low magnetic field induced strong magnetoelectric coupling in three phase composite films with ferroelectric domain switchability

We report the dielectric, ferroelectric, magnetic and magnetoelectric properties of three-phase composite thick films (thickness~0.25 mm) of BaFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as BaFBT60) and SrFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as SrFBT60). A very strong magnetoelectric voltage coefficient (α33) of about 60 mV/cmOe and 40 mV/cmOe was observed at a small magnetic field of 300 Oe for the BaFBT60 and SrFBT60 films, respectively. The nature of the zero field cooling as well as the field cooling curves of composite films was suggested as a spin-glass type behavior. A remarkable value of magnetocapacitance (MC) of about 7.2% was observed for BaFBT60 composite film. The switchability phenomena of the ferroelectric domains were observed in the presence of the magnetic field of about 700 Oe. In addition, very significant information about the domain wall mobility was obtained from the irreversible (α) and reversible (ϵre) coefficients as calculated from the Rayleigh analysis.

Structural and multiferroic properties of trilayer green magnetoelectric Co0.8Ni0.2Fe2O4/K0.25Na0.75NbO3/Co0.8Ni0.2Fe2O4 composite structure

We have investigated the structural, dielectric, magnetic-magnetostrictive, ferroelectric-piezoelectric and magnetoelectric (ME) properties of green (Pb-free) Co0.8Ni0.2Fe2O4/K0.25Na0.75NbO3/Co0.8Ni0.2Fe2O4 (CNFO/KNN/CNFO) trilayer laminate (2-2) multiferroic composite structure. Magnetostrictive Co0.8Ni0.2Fe2O4phase was synthesized by the solution combustion technique and the piezoelectric K0.25Na0.75NbO3 phase was synthesized by a solid-state method. The trilayer ME laminate composite structure of CNFO-KNN phases fabricated by silver epoxy adhesive bonding technique. The magnetostrictive Co0.8Ni0.2Fe2O4 phase exhibits a piezomagnetic coefficient of −0.029 ppm/Oe at 1500 Oe magnetic field. The piezoelectric K0.25Na0.75NbO3 showed a piezoelectric charge coefficient of d33 ~57 pC/N. The trilayer CNFO/KNN/CNFO laminate structure reveals the ME coefficient (αME) of 3.06 mV/Oe·cm which is relatively higher than the 0–3 connectivity composite structures. Here, we have discussed the fabrication technique for multiferroic laminate structures for the green magnetoelectric device having αME ~3.06 mV/Oe·cm with their magnetic/magnetostrictive and ferroelectric/piezoelectric properties.

A comparison of converse magnetoelectric coupling effect of YIG film on FE and AFE ceramic substrates

The magnetoelectric properties of laminated heterostructures consisting of ferromagnetic yttrium iron garnet (YIG) films deposited on antiferroelectric (AFE) (Pb0.97La0.02)(Zr0.6Sn0.3Ti0.1)O3 (PLZST) and on ferroelectric (FE) 0.75Pb(Mg1/3Nb2/3)O3-0.25Pb(Zr0.48Ti0.52)O3 (PMN-PZT) ceramics are compared in this work. In particular, the Converse Magneto Electric (CME) coefficient is evaluated for these two types of structures. When the electric field is applied on an AFE ceramic, the CME coefficient peaks at the switching field and, without bias magnetic field, the maximum value is 11.6 × 10−8 s/m. In case of a FE ceramic, at the electric coercive field, the CME coefficient can reach 17 × 10−8 s/m at 0 Oe. Each structure has advantages and disadvantages depending on the applications.

Temperature dependent crossover between positive and negative magnetoresistance in graphene nanocrystallines embedded carbon film

Monitoring magnetoelectric transport behavior of graphene material is critical in establishing a foundation for engineering next-generation spintronic devices. Here we report a temperature-dependent crossover between positive and negative magnetoresistance (MR) in graphene nanocrystallines embedded carbon film (GNC film), two sign changes of MRTotal (where MRTotal presents the measured MR value) value from positive MRTotal(+) to negative MRTotal(−) and then back to MRTotal(+) are observed as temperature varies from 2 K to 400 K. The crossover can be ascribed to the competitions among different origins including wave function shrinkage, spin-dependent Coulomb blockade effect and Lorentz force, which play dominant roles in low, medium and high temperatures, respectively. Moreover, it is revealed that GNC film with smaller GNs has larger positive contribution to MRTotal behavior, resulting in maximum MRTotal(+) of ∼8.1%. In contrast, GNC film with larger GNs dramatically contributes to negative MRTotal behavior, which obtains maximum MRTotal(−) of ∼ -1.1%. This work deepens understanding about the origin of MR of nanometer-sized graphene, which provides guidance for further magnetoelectric property improvement, and paves a way towards specific design of graphene derived spintronic devices with controllable MR behavior.

Correlation of octahedral distortion with vibrational and electronic properties of LaFe1-xTixO3 nanoparticles

LaFeO3 is a multiferroic with multiple functionalities. It demonstrates room-temperature magnetism. A prime interest in this material is to introduce formidable ferroelectricity in LaFeO3 that may improve its functionalities with magnetoelectric properties. Ti4+ has a higher charge and smaller ionic radii. Such changes may modify bond lengths, bond angles, octahedral tilting and oxygen content. As a result, the nature of crystallinity can be modified. As a consequence, the electronic properties like the band gap, transport properties may get influenced. Titanate perovskites are known to be ferroelectric materials. Intending to strengthen the ferroelectric properties of a magnetic LaFeO3, this work investigates the structural, vibrational and electronic properties of LaFe1-xTixO3 (0 ≤ x ≤ 0.50). The novelty of this work is on an in-depth study of the bond lengths and bond angles correlated with BO6 octahedra and La8O6 cage distortion. Ti substitution affects the entire perovskite structure by introducing a vertical flattening of the BO6 octahedra as well as the La8O6 cage. The strong hybridization of Ti4+ with O2− may be responsible for such modifications. The locus of octahedral apical oxygen fluctuates, influencing the tilting angle of the BO6 octahedra. This may be a result of the nature of the substituted cations and the oxygen acceptability limit of the lattice. The phonon modes and their modification have been correlated. The transport properties are modified with an external magnetic field.

Ferromagnetic behaviors in monolayer MoS2 introduced by nitrogen-doping

Effective functionalization of magnetic properties through substitutional doping may extend the spintronic applications of two-dimensional (2D) semiconductor MoS2. Here, the magnetoelectric properties of nitrogen-doped monolayer MoS2 are investigated by first-principles calculations, revealing that the N-p and S-p states are strongly hybridized with the Mo-d states, thus leading to the appearance of magnetism as verified experimentally. We demonstrate in situ doping of monolayer MoS2 with nitrogen via a convenient chemical vapor deposition method. Incorporation of nitrogen into MoS2, leading to the evolution of magnetism, is evidenced by combining x-ray photoelectron spectroscopy and vibrating sample magnetometer measurements. By comparison with pristine monolayer MoS2, the distinct ferromagnetism behaviors of nitrogen-doped monolayer MoS2 are observed up to room temperature, while the semiconducting nature persists. Our work introduces an efficient and feasible approach to realize magnetism in the 2D limit and explores potential applications in semiconductor spintronics.

New insights on the structural and optical-vibration properties of noncentrosymmetric lanthanides pyrogermanates

A complete series of noncentrosymmetric Ln2Ge2O7 materials (Ln = lanthanides) were obtained by the molten-salts processing route. Triclinic (P1 space group) as well as tetragonal (P41212 space group) structures were observed, respectively, for the La–Eu compounds (larger ions) and for the Gd–Lu ones (smaller ions). The optical-vibration properties of both groups of samples were well investigated by Raman spectroscopy besides group-theory calculations. All the predicted phonon modes were discerned for the triclinic polar phase, while the most significant phonon modes of the tetragonal phase were determined. Beside the well-known classical dependence of the phonon wavenumbers with the ionic radii of the lanthanide (hardening of the higher-frequency modes from La to Lu), it was observed an opposite softening of the low-frequency modes within the triclinic phase (La–Eu samples). This result could be related to the contribution of the increasing lanthanide masses, added to the high lattice anharmonicity near the phase boundary between the triclinic and tetragonal phases, which can be a consequence of the strong changes in the coordination numbers of the Ln-polyhedra. Once the polar triclinic phase and the noncentrosymmetric tetragonal structure are thermally stable, and owing to the low-temperature magnetic features already shown by of non-cubic Ln2Ge2O7 compounds, we believe that some of these materials could present magnetoelectric or related properties.

Lack of linear magnetoelectric effect in ferrimagnetic distorted honeycomb Ni4Nb2O9

M 4 A 2O9 transition metal oxides, with M a divalent cation and A Nb or Ta, that exhibit a structure derived from corundum constitute an interesting class of materials due to their possible magnetoelectric properties. The lack of a linear magnetoelectric effect in Ni4Nb2O9, unlike Mn4Nb2O9 or Co4Nb2O9, is explained by a comprehensive investigation, combining synchrotron x-ray and neutron diffraction with magnetization, dielectric, and polarization measurements. The m′m′m magnetic point group associated with the Pb′cn′ ferrimagnetic structure induced below 76 K by the orthorhombic Pbcn structure of Ni4Nb2O9 forbids indeed such an effect. The crystal structure and magnetic ground state of Ni4Nb2O9 are discussed and compared with those of magnetoelectric P3¯c1M4A2O9 compounds whose structure derives from corundum.

Suppression of magnetoelectric effects in DyCrO4 by chemical doping

The scheelite-type DyCrO4 shows a large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity. In this article, we investigate the Bi-doping effects on the crystal structure, magnetism, dielectric constant, and electric polarization for a Dy1−xBixCrO4 (x = 0, 0.05, 0.1) solid solution. The substitution of Bi for Dy up to 10% does not change the structure and antiferromagnetic ordering temperature very much. However, it remarkably suppresses the magnetodielectric effect from 14% in the parent phase to 3.2% in the x = 0.1 sample. More sharply, the maximum field-induced electric polarization is reduced from 320 μC/m2 (x = 0) to 10 μC/m2 (x = 0.1). The results reveal that Dy plays a crucial role in the origin of the large linear magnetoelectric effect of DyCrO4, so chemical doping on this site provides an effective method to manipulate the magnetodielectric and magnetoelectric properties.