Room Temperature Multiferroic Properties Research Articles

Effect of nano-size on magnetostriction of BiFeO3 and exceptional magnetoelectric coupling properties of BiFeO3_P(VDF-TrFE) polymer composite films for magnetic field sensor application

The existence of magnetostriction in bulk BiFeO3 is still a matter of investigation and it is also an issue to investigate the magnetostriction effect in nano BiFeO3. Present work demonstrates the existence of magnetostrictive strain in superparamagnetic (SPM) BiFeO3 nanoparticles at room temperature and the magnetoelectric (ME) coupling properties in composite form with P(VDF-TrFE). Despite few reports on the magnetostriction effect in bulk BiFeO3 evidenced by the indirect method, the direct method (strain gauge) was employed in this work to examine the magnetostriction of SPM BiFeO3. In addition, a high ME coupling coefficient was observed by the lock-in technique for optimized BiFeO3_P(VDF-TrFE) nanocomposite film. These nanocomposite films also exhibit room-temperature multiferroic properties. These results provide aspects of material with immense potential for practical applications in spintronics and magneto-electronics applications. We report a ME sensor using SPM BiFeO3_P(VDF-TrFE) nanocomposite film for detection of ac magnetic field.

Investigations of room temperature multiferroic and magneto-electric properties of (1-Φ) PZTFT-Φ CZFMO particulate composites

Multiferroic composites consisting of a single-phase multiferroic [0.6(PbZr0.53Ti0.47O3)-0.4(PbFe0.5Ta0.5)O3] as a matrix and a magnetostrictive phase (Co0.6Zn0.4Fe1.7Mn0.3O4) dispersed in the matrix are fabricated via hybrid synthesis technique. The structure and surface morphology studies using x-ray diffraction and field emission scanning electron microscopy techniques indicate the formation of 3-0 type particulate composites. Coexistence of soft-magnetic behavior and ferroelectric characteristics are confirmed for composites from magnetization vs magnetic field (M–H) and polarization vs electric field (P–E) measurements, respectively. Magneto-dielectric (MD) measurement shows significant changes in the dielectric properties with the application of a magnetic field, indicating the existence of strong MD behavior. The biquadratic nature of magneto-electric (ME) coupling is described by the Landau free energy equation arising from the strain transfer at the interfaces between the constituent phases. The direct magneto-electric voltage coefficient measurement also confirms very strong coupling between ferroelectricity and magnetism and supports the strain-mediated magneto-electric effect in composites. The Φ = 0.3 composite exhibits the maximum ME coefficient of 20.72 mV/cm Oe with MS = 24.62 emu/g, HC = 59.66 Oe, and piezoelectric coefficient value d33 = 19 pC/N. The strong magneto-electric effect along with low dielectric loss at room temperature in these composites suggests their suitability for multifunctional magneto-electric device applications such as magnetic sensors, etc.

Evidence of direct and converse magnetoelectric coupling in eco-friendly 0.75(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)–0.25(CoFe2O4) particulate composite

Magnetoelectric (ME) multiferroic composite exhibits the ME effect, and their interaction between piezoelectric and magnetic phase is measured in terms of ME coupling (α). ME coupling is an interesting and characteristic property of ME materials and can be evaluated by direct and indirect methods. In this work, the solid-state sintering technique has been adopted to synthesize the lead-free 0.75(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)–0.25CoFe2O4 (NBBT-CFO) composite. The X-ray diffraction patterns and uniform distribution of closely packed grains reveal the coexistence of constituent phases in the composite. This composite reveals room-temperature multiferroic properties. The room temperature dielectric constant (ε′) of the poled sample displays the resonance and anti-resonance peaks at a particular frequency ∼ 455 kHz and 450 kHz, respectively. The estimated value of the electromechanical coupling coefficient (kP) is 16.69%. The direct ME and converse ME coupling study has been done through the Polarization (P) vs Electric field (E) and Magnetization (M) vs Magnetic field (H) hysteresis loop measurements of magnetically and electrically poled and unpoled samples, respectively. The variation in the polarization and magnetization value reveals the presence of direct and converse ME coupling in the composite.

Technological Peculiarities of Epsilon Ferrite Epitaxial Stabilization by PLD

The present paper describes the technological peculiarities relevant to the nucleation and further epitaxial growth of the metastable epsilon phase of iron oxide by means of pulsed laser deposition (PLD). The orthorhombic epsilon ferrite ε-Fe2O3 is an exotic member of a large family of iron oxide polymorphs, which attracts extensive attention nowadays due to its ultra-high magneto-crystalline anisotropy and room temperature multiferroic properties. Continuing the series of previous publications dedicated to the fabrication of ε-Fe2O3 films on GaN, this present work addresses a number of important requirements for the growing conditions of these films. Among the most sensitive technological parameters, the growth temperature must be high enough to aid the nucleation of the orthorhombic phase and, at the same time, low enough to prevent the thermal degradation of an overheated ε-Fe2O3/GaN interface. Overcoming the contradicting growth temperature requirements, an alternative substrate-independent technique to stabilize the orthorhombic phase by mild aluminum substitution is proposed. The advantages of this technique are demonstrated by the example of ε-Fe2O3 films PLD growth carried out on sapphire—the substrate that possesses a trigonal lattice structure and would normally drive the nucleation of the isostructural and energetically more favorable trigonal α-Fe2O3 phase. The real-time profiling of high-energy electron diffraction patterns has been extensively utilized throughout this work to keep track of the orthorhombic-to-trigonal balance being the most important feed-back parameter at the growth optimization stage.

Effect of pH value on multiferroic properties of barium ferrite ceramics prepared by sol–gel method

In this paper, BaFe12O19 (BaM) ceramics at different pH values were prepared by sol–gel method. Effects of pH value on the microstructure, electrical as well as magnetic properties were systematically studied. XRD indicate that the ceramics were mainly BaM. However, with the pH value increasing further, the BaFe2O4 impurity phase appears gradually in both powders and ceramics due to the degree of complexation between citric acid and metal cations and other reasons. SEM results show that the grain size of ceramics decreases from 2.28 μm to 1.35 μm with the pH value increase from 4 to 8. It is found that room temperature dielectric constant, residual polarization, and saturation magnetization of the ceramics is the largest when the pH value of the solution is 4, which are 0.108 μC/cm2 and 32.829 emu/g, respectively. The dielectric constant and residual polarization of ceramics decrease with the increase of pH value. The ferroelectric and magnetic hysteresis loops have confirmed room-temperature multiferroic properties of the prepared ceramics. It laid the foundation for the further development of new room temperature single-phase multi-iron materials.

Multiferroic and Magnetodielectric Effects in Multiferroic Pr2FeAlO6 Double Perovskite.

Single-phase multiferroics that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, and offer a fundamental platform for novel functionality. In this work, a double perovskite multiferroic Pr2FeAlO6 ceramic is prepared using a sol-gel process followed by a quenching treatment. The well-crystallized and purified Pr2FeAlO6 in trigonal structure with space group R3c is confirmed. A combination of the ferroelectric (2Pr = 0.84 μC/cm2, Ec = 7.78 kV/cm at an applied electric field of 20 kV/cm) and magnetic (2Mr = 433 memu/g, Hc = 3.3 kOe at an applied magnetic field of 1.0 T) hysteresis loops reveals the room-temperature multiferroic properties. Further, the magnetoelectric effect is observed from the measurements of magnetically induced dielectric response and polarization. The present results suggest a new complex oxide candidate for room-temperature multiferroic applications.

Enhancement of ferromagnetism in a multiferroic La–Co co-doped BiFeO3 thin films

BiFeO3-based materials have attracted considerable attention owing to their room-temperature multiferroic properties and ultrahigh ferroelectric polarization. In this study, La and Co co-doped BiFeO3 (BLFCO) thin films were fabricated on Pt (111)/Ti/SiO2/Si substrate buffered by Nb-doped (0.7 wt.%) SrTiO3 via pulsed laser deposition. Experiments revealed that the film deposited at 0.2 Pa comprised the predominant orientation of BiFeO3 (BFO) (111), and its surface root-mean-square roughness was 0.96 nm. The saturation magnetization of the film reached 25.3 emu cm3, which was an order of magnitude higher than that of the pure BFO film, as well as the remanent magnetization reached 1.8 emu cm−3. The result was attributed to the predominant orientation and small grain size of BLFCO films. The piezo-response force microscopy measurements revealed the co-doped film possesses well repeatable performance of polarization reversal, and the presence of ferroelectric orders with an asymmetric ‘butterfly’ structure. These results are helpful for further improving the performance of BFO multifunctional devices.

Room-temperature multiferroic properties of Al-doped hexaferrites sintered at high oxygen atmospheric concentrations

The room-temperature magnetoelectric effects of Al-doped polycrystalline hexaferrites Sr3Co2(Fe1-xAlx)24O41(x = 0.00, 0.02, and 0.04) sintered under high oxygen atmospheric concentrations were comprehensively investigated. The magnetic phases and magnetic structures were modulated by high sintering oxygen atmospheric concentrations as demonstrated by M-T tests and magnetic hysteresis loops. Compared with previous specimens sintered under low oxygen atmospheric concentrations, the transverse conical spin structures of the Sr3Co2(Fe1-xAlx)24O41(x = 0.00, 0.02, and 0.04) were obviously strengthened by high sintering oxygen atmospheric concentrations, exhibiting magnetoelectric effects in high magnetic field ranges (>1 T).

Correlation between crystal structure and magnetism in PLD grown epitaxial films of ε-Fe2O3 on GaN

ABSTRACT In the present paper we discuss correlations between crystal structure and magnetic properties of epitaxial ε-Fe2O3 films grown on GaN. The large magnetocrystalline anisotropy and room temperature multiferroic properties of this exotic iron oxide polymorph, make it a perspective material for the development of low power consumption magnetic media storage devices. Extending our recent progress in PLD growth of ε-Fe2O3 on the surface of technologically important nitride semiconductors, we apply reciprocal space tomography by electron and x-ray diffraction to investigate the break of crystallographic symmetry occurring at the oxide-nitride interface resulting in the appearance of anisotropic crystallographic disorder in the sub-100 nm ε-Fe2O3 films. The orthorhombic-on-hexagonal nucleation scenario is shown responsible for the development of a peculiar columnar structure observed in ε-Fe2O3 by means of HRTEM and AFM. The complementary information on the direct and reciprocal space structure of the columnar ε-Fe2O3 films is obtained by various techniques and correlated to their magnetic properties. The peculiar temperature dependence of magnetization studied by the small-field magnetization derivative method and by neutron diffraction reveals the existence of a magnetic softening below 150 K, similar to the one observed earlier solely in nanoparticles. The magnetization reversal in ε-Fe2O3 films probed by X-ray magnetic circular dichroism is found different from the behavior of the bulk averaged magnetization measured by conventional magnetometry. The presented results fill the gap between the numerous studies performed on randomly oriented ε-Fe2O3 nanoparticles and much less frequent investigations of epitaxial epsilon ferrite films with lattice orientation fixed by the substrate.

Coexistence of two ferroelectric phases and improved room-temperature multiferroic properties in the (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3 system

In the present time, the focus of many researchers is to enhance the multiferroic properties of pure and doped BiFeO3 (BFO) based materials. However, the materials community has not yet achieved the desired multiferroic properties in single doped BiFeO3. Therefore, we decided to start with the well known system BiFeO3–PbTiO3, with good ferroelectric properties, as compared to undoped BFO and Co2+ as dopant, to obtain the (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3 system. In this paper, the structural, magnetic, and ferroelectric properties of (0.70)BiFe1 − xCoxO3–(0.30)PbTiO3, with 0.00 ≤ × ≤ 0.12, prepared by a simple solgel route is presented. The inclusion of Co2+ leads to notable changes in the structural and magnetic properties. X-ray diffraction studies revealed that the samples crystallize into two ferroelectric phases: rhombohedral (R3c) and tetragonal (P4mm) up to x = 0.06; afterward, it leads to nearly a single phase tetragonal structure for x = 0.09 and 0.12. The magnetic properties are enhanced in a significant manner with Co2+ doping and are ascribed to structural changes (change in Fe–O–Fe bond length) and the suppression of the spiral spin structure characteristic of BiFeO3. The theoretical analysis of the magnetic data shows that the ferromagnetic part also increases with Co2+ doping. Ferroelectric properties are also enhanced with Co doping due to a decrease in the DC current density. The observed room temperature multiferroic properties of this compound foresee great potential for magnetoelectric devices.

Room temperature multiferroic properties and polymorphic phase transition-induced noticeable magnetodielectric anomalies in Fe/Co co-doped (K0.52Na0.48)NbO3 ceramics

Abstract Polycrystalline ceramics of (K0.52Na0.48)Nb1-x(FeCo)xO3 (0 ≤ x ≤ 0.02) are synthesized using solid-state reaction method. Appropriate Fe/Co doping (x = 0.010 and 0.015) not only optimizes room temperature ferroelectricity of KNNFC ceramics, but also effectively introduces room temperature ferromagnetism and large magnetodielectric effects. The Fe2+/3+-O-Co2+/3+ ferromagnetic double exchange is considered the main reason for the enhancement in ferromagnetic. Moreover, magnetic anomalies and noticeable magnetodielectric (MD) peaks are found near the ferroelectric rhombohedral-orthorhombic (R–O) polymorphic phase transition, indicating the presence of spin-lattice coupling in these samples. Meanwhile, the Fe2+-Fe3+, Co2+-Co3+, and/or Fe2+/3+-Co2+/3+ local dipoles that begin to appear near the R–O phase transition temperature can also contribute to the MD effect. When x = 0.015, the MD peak is as large as +12% (0.9 T, 106 Hz, 120 K), and the room temperature MD value reaches −7% (0.9 T, 106 Hz).

Structural, strong magnetic exchange, and room temperature multiferroic properties of single-phase 0.75BiFeO3–BaFe1/2Nb1/2O3 bulk ceramics

The ceramic 0.75BiFeO3–BaFe1/2Nb1/2O3 (0.75BF–BaFN) exhibits enhanced magnetisation and polar order regions at room temperature. This study investigated the microscopic structure and the magnetic, ferroelectric, magneto-ferroelectric, and optical properties of 0.75BF–BaFN by conducting experiments and performing density functional theory (DFT) calculations. Evidence of weak amplitude R-type octahedral rotations was observed using transmission electron microscopy (TEM). X-ray diffraction (XRD) refinement revealed that the P1 space group more appropriately described the structure of 0.75BF–BaFN. The weak influence of the magnetic field H on the polarisation of 0.7BF–BaFN and 0.75BF–BaFN ceramics was investigated. A notable magnetic enhancement was observed in 0.75BF–BaFN ceramics with a saturation magnetisation of 0.19 μB per Fe. DFT calculations predicted that the stable magnetic configuration of 0.75BF–BaFN is a G-type antiferromagnetic (AFM) structure. This study found stronger magnetic interactions between first-neighbour Fe ions (Ja = 12 meV) compared to pure BiFeO3. With a significant remanent moment, strong exchange coupling, and magnetic field control of polarisation, 0.75BF–BaFN may facilitate the development of room temperature single-phase magnetoelectric components.

Synthesis and room-temperature multiferroic properties of lead-free Bi4Ti3O12/NiFe2O4 nanocomposite films

Lead-free Bi4Ti3O12/NiFe2O4 nanocomposite films have been prepared via sol-gel spin-coating route. The successful phase formation of orthorhombic Bi4Ti3O12 and cubic NiFe2O4 has been confirmed using x-ray diffraction without any detectable extra phase. The scanning electron microscopy with EDS measurement reveals homogeneous and dense growth of both phases accompanied by clear interface between the two layers. The loop of magnetization versus magnetic field indicates the ferromagnetic properties at room temperature with saturation magnetization of ~257.48 emu/cm3, coercive field of ~121 Oe and remnant magnetization of ~57.03 emu/cm3. Room-temperature ferroelectric behavior is also obtained along with the good fatigue endurance properties and low leakage current density. The frequency dependence of dielectric constant displays the monotonous decreasing tendency with low dielectric loss. Moreover, evident magnetodielectric behavior is achieved in the nanocomposite films at room temperature. The coexistence of ferromagnetic and ferroelectric behavior including the appearance of magnetodielectric effect proves the room-temperature multiferroic properties in Bi4Ti3O12/NiFe2O4 nanocomposite films, which makes the films meaningful as the lead-free multiferroic systems for device applications at room temperature.

Investigation of room temperature multiferroic properties in sol-gel derived gadolinium, cobalt doped BiFeO3 nanoceramics

Detailed studies of structural, dielectric, magnetic, ferroelectric, and optical properties of a chemically sol-gel synthesized series of Bi1 − xGdxFe1 − yCoyO3 (x = 0, 0.1 and y= 0, 0.1) nanoceramics are presented. These nanoceramics attract attention as promising candidates for application as room temperature multiferroics in spintronics devices, exhibiting an optimistic set of properties. The average particle sizes of all the samples are calculated, and it was found to be ∼45 nm from the Scanning Electron Microscopy image. The dielectric behavior of the prepared nanoceramics was investigated over a wide frequency (100 Hz–103 kHz) and a temperature (35–350 °C) range. Interestingly, a low temperature dielectric anomaly is observed at around 170 °C for Bi0.9Gd0.1Fe0.9Co0.1O3 due to the magnetoelectric coupling. A noticeably large value of dielectric constant (∼990) and a low tan δ loss have also been observed for this nanoceramic at room temperature. The complex impedance spectroscopic analysis was also performed by plotting Nyquist plots, and the corresponding activation energies are evaluated from the Arrhenius fittings. Magnetization measurements of the samples reveal the presence of weak ferromagnetism due to surface spins as well as a noticeable improvement in the magnetic properties with Gd and Co doping. Ferroelectric properties have also been observed to be slightly improved because of doping, though it becomes somewhat lossy for Gd and Co doped samples. All the promising improved properties directly depend on the subsequent increase in the bandgap from 2.29 eV to 2.45 eV, with doping in the parent BiFeO3 compound confirmed from UV–Vis spectroscopy.

Enhanced magnetoelectric coupling and dielectric constant in flexible ternary composite electrospun fibers of PVDF-HFP loaded with nanoclay and NiFe2O4 nanoparticles

Magnetoelectric flexible composite fiber mats with superior room temperature magnetoelectric properties.

Structural and Magnetic properties of Room Temperature Multiferroic Lu0.9Ho0.1FeO3

In recent times, LuFeO3 is found to be an interesting material exhibiting room temperature multiferroic properties both in its stable orthorhombic and meta-stable hexagonal phase [1, 2]. To stabilize the single phase and also to enhance the magnetic and ferroelectric properties rare earth doping is a possibility [3, 4]. In this work, magnetic rare earth atom, Holmium is doped in place of Lu, the structural, magnetic and ferroelectric properties are investigated. Bulk nanocrystallineLu0.9Ho0.1FeO3 compound is synthesized by hydrothermal method. Doping with ionic radius larger than Lu, helps to stabilize the structure in a stable orthorhombic- Pnma phase. Rietveld refinement of structural data is carried out on the synthesized sample and the lattice parameters are found to be increasing as expected. Also, Ho being an element with a large magnetic moment, the effect of doping on magnetic properties is investigated. M-H isotherms didn’t saturate even at magnetic field, H= 9T reflecting a strong antiferromagnetic interaction that arises from the super exchange Fe3+-O-Fe3+ interactions. Finite remnant and coercivity values obtained from the M-H loop measured at 300 K confirms that the TN lies above room temperature (RT). Observation of P-E loop at 300 K confirms ferroelectric ordering at RT.

Dielectric and ferroelectric properties of Nd3Fe5O12

Multiferroics have attracted research interest for decades due to their potential applications. Multiferroics are relatively scarce due to the mutual exclusivity between magnetic and ferroelectric properties. New room-temperature multiferroics are looking forward to be exploited. Room-temperature multiferroic properties have been observed in a new rare-earth iron garnet (REIG), Nd3Fe5O12 (NdIG). The dielectric properties of NdIG over a wide temperature range (300 K–650 K) at different frequencies (100 Hz–1 MHz) and in the temperature range from 70 K to 300 K at 100 Hz are investigated herein. The results show that this material has two dielectric relaxations in the temperature range from 290 K to 525 K and a dielectric anomaly around the magnetic ordering temperature (565 K). The first dielectric relaxation in the temperature range from 290 K to 500 K is attributed to the conduction with an activation energy of 0.75 eV. The other dielectric relaxation in an elevated temperature range has an activation energy of 0.87 eV, which originates from the inhomogeneous structure. Furthermore, the ferroelectric polarization of approximately 28 μC/m2 at 77 K is determined by the positive-up-negative-down method and induced by the effective magnetic field created by the iron sublattice magnetic ordering and electric-dipole moments of the neodymium ions.

Influences of annealing temperature on dielectric, magnetic and magnetoelectric coupling properties of 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 ceramics

Multiferroic 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 ceramics were prepared by sol-gel method with various temperatures ranging from 950 to 1100 °C. The influence of annealing temperature on structure, morphology, dielectric, magnetic and magnetoelectric coupling effect was investigated. The refinement of x-ray diffraction data and the thermogravimetric-differential thermal analysis indicated the coexistence of perovskite and spinel phases with annealing temperature above 950 °C. Increasing grain size in surface morphology measurement was closely related to the increasing annealing temperature. Enhancement in dielectric properties was observed with increasing annealing temperature. The room-temperature ferromagnetic properties were also detected with saturated magnetic hysteresis loops under different annealing temperatures. Finally, magnetoelectric coupling effect was confirmed in the samples. The possible factors for room-temperature multiferroic properties were discussed with increasing annealing temperature. This study showed that annealing temperature could evidently affect the multiferroic properties in 0.7Bi0.5Na0.5TiO3-0.3NiFe2O4 solid solution.

Two-Phase Room-Temperature Multiferroic Nanocomposite with BiMnO3-Tilted Nanopillars in the Bi2W1-xMnxO6 Matrix.

Single-phase multiferroics are scarce because of the fact that the coexistence of magnetism (spin order) and ferroelectricity (electric dipole order) in a single-phase material may be limited. Taking advantage of the nanocomposite design, combining a ferroelectric phase and a ferromagnetic phase presents enormous opportunities in multiferroic material exploration. In this work, a new 2D-layered framework of Bi2W1-xMnxO6-BiMnO3 (BWMO-BMO) in the nanocomposite thin-film form has been demonstrated and shows obvious room-temperature multiferroic properties, that is, ferroelectric and ferromagnetic at room temperature. The BMO phase forms a unique tilted domain structure in the BWMO matrix, and both phases are of excellent epitaxial quality. The ferroelectric response originates from the layered Aurivillius phase of the BWMO matrix, and the ferromagnetic properties mainly arise from the BMO nanodomains. Moreover, the band gap of the BWMO-BMO nanocomposite is effectively tuned to 3.10 eV from its original 3.75 eV of BWO. This study demonstrates a new design of nanocomposite using layered oxides toward future multifunctional oxides for nanoscale devices.

Room-temperature multiferroicity in CeFeO3 ceramics

The cerium orthoferrite (CeFeO3) ceramics were synthesized successfully by solid-state method and the room-temperature multiferroic properties of CeFeO3 annealed under different atmospheres were investigated. A clear ferroelectric hysteresis loop with Pr = 0.8 μC/cm2 measured under 10 kV/cm is observed at room temperature in the CeFeO3 annealed under oxygen, implying the nature of ferroelectricity existing in the material which is ascribed to the crystal structure change and local lattice distortion closely related to the mixed valences of Ce and Fe ions, as revealed by X-ray diffraction, Raman spectra, and XPS analysis. Besides, Magnetic study reveals that CeFeO3 is a weak ferromagnetic material and the saturation magnetization increases with oxygen vacancies decreasing. The coexistence of the induced ferroelectricity and the improved ferromagnetism confirms that the better multiferroic property exists in CeFeO3 ceramics and the oxygen content (Ce valence) has a critical role in the ferroelectric property.