Multiferroic Nanocomposite Research Articles

Vertically Aligned Nanocomposite BaTiO3:YMnO3 Thin Films with Room Temperature Multiferroic Properties toward Nanoscale Memory Devices

Self-assembled epitaxial BaTiO3:YMnO3 (BTO:YMO) vertically aligned nanocomposite thin films have been fabricated on SrTiO3 (001) substrates using pulsed-laser deposition. A room temperature multiferroic response has been demonstrated in the thin films. Enormous strain has been generated in both phases (e.g., 1.4% compressive strain in BTO and 6.8% tensile strain in YMO out-of-plane) because of the large lattice mismatch. By tuning the deposition frequency, the microstructure and strain of the nanocomposite films are tailored, which leads to the property tuning in the nanocomposite films. It is found that strain plays an important role on the magnetic ordering of YMO and thus results in the room temperature ferromagnetic response. Combined with the ferroelectric response in the BTO:YMO nanocomposite thin films, a new room temperature multiferroic two-phase nanocomposite has been demonstrated. The room temperature magnetoelectric coupling has been demonstrated for this new system. Overall, the BTO:YMO thin ...

Design of a Vertical Composite Thin Film System with Ultralow Leakage To Yield Large Converse Magnetoelectric Effect.

Electric field control of magnetism is a critical future technology for low-power, ultrahigh density memory. However, despite intensive research efforts, no practical material systems have emerged. Interface-coupled, composite systems containing ferroelectric and ferri-/ferromagnetic elements have been widely explored, but they have a range of problems, for example, substrate clamping, large leakage, and inability to miniaturize. In this work, through careful material selection, design, and nanoengineering, a high-performance room-temperature magnetoelectric system is demonstrated. The clamping problem is overcome by using a vertically aligned nanocomposite structure in which the strain coupling is independent of the substrate. To overcome the leakage problem, three key novel advances are introduced: a low leakage ferroelectric, Na0.5Bi0.5TiO3; ferroelectric-ferrimagnetic vertical interfaces which are not conducting; and current blockage via a rectifying interface between the film and the Nb-doped SrTiO3 substrate. The new multiferroic nanocomposite (Na0.5Bi0.5TiO3-CoFe2O4) thin-film system enables, for the first time, large-scale in situ electric field control of magnetic anisotropy at room temperature in a system applicable for magnetoelectric random access memory, with a magnetoelectric coefficient of 1.25 × 10-9 s m-1.

FEM‐analysis of a multiferroic nanocomposite – comparison of experiment and numerical simulation

AbstractThe combination of electric and magnetic materials opens new possibilities in the field of sensor technologies and data storage [1]. These magneto‐electric (ME) materials have the property to change a physical ferroic quantity into another, i.e. a magnetic field can change the electric polarization and vice versa. The combination of multiple ferroic characteristics within materials is called multiferroic. Since magneto‐electric single‐phase materials are rare in nature and typically operate only at very low temperature, they are not favorable in technical applications. However, ME composites, consisting of ferroelectric and ferromagnetic phases, produce a strain‐induced magneto‐electric product property at room temperature [2]. In these composites, two different effects can be differentiated, the direct and the converse ME effect. The first one describes a polarization which is magnetically caused. In detail, a magnetic field is applied which produces a deformation of the magneto‐active phase which is transferred to the electro‐active phase and as a consequence this phase exhibits a polarization. Therefore, one can discover a strain‐induced polarization. The second effect to observe is a magnetization caused by an electric field. In our contribution, we focus on a (1‐3) composite, where cobalt ferrite nanopillars are embedded in a barium titanate matrix, see the experiments described in [3]. In the numerical simulations we compare the changes of the strain‐induced inplane polarizations of the ferroelectric matrix with experimental measurements. Furthermore, we analyze the magneto‐electric coupling coefficient. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetoelastoelectric coupling in core-shell nanoparticles enabling directional and mode-selective magnetic control of THz beam propagation.

Magnetoelastoelectric coupling in an engineered biphasic multiferroic nanocomposite enables a novel magnetic field direction-defined propagation control of terahertz (THz) waves. These core-shell nanoparticles are comprised of a ferromagnetic cobalt ferrite core and a ferroelectric barium titanate shell. An assembly of these nanoparticles, when operated in external magnetic fields, exhibits a controllable amplitude modulation when the magnetic field is applied antiparallel to the THz wave propagation direction; yet the same assembly displays an additional phase modulation when the magnetic field is applied along the propagation direction. While field-induced magnetostriction of the core leads to amplitude modulation, phase modulation is a result of stress-mediated piezoelectricity of the outer ferroelectric shell.

Comparative studies of the dielectric properties of (1−x)BiFeO3-xNi0.8Zn0.2Fe2O4 (x=0.0, 0.2, 0.5, 0.8, 1.0) multiferroic nanocomposite with their single phase BiFeO3 and Ni0.8Zn0.2Fe2O4

BiFeO3 (BFO) and nickel zinc ferrite Ni0.8Zn0.2Fe2O4 (NZFO) were prepared by sol gel and auto combustion route respectively. Stoichiometric proportions were mixed to obtain the multiferroic nanocomposites having the compositional formula (1−x)BiFeO3-x Ni0.8Zn0.2Fe2O4 (x=0.0, 0.2, 0.5, 0.8, 1.0). The phases were confirmed by XRD analyses. SEM micrographs showed the agglomerated nature of the particles with continuous grain growth in all directions. Elemental compositions were confirmed from EDAX studies. FTIR studies showed the stretching and bending vibrations of the various bonds present in the samples. The dielectric properties such as dielectric constant, ε′ and dielectric loss tangent, tanδ were studied for the spinel, perovskite and nanocomposite ferrites. Experimental result shows an increasing trend in the value of dielectric constant in going from spinel to perovskite phase. The frequency dependence of tanδ showed minimum loss for x=0.5 nanocomposite. Possible mechanisms explaining the above results were being discussed.

Development of multiferroic polymer nanocomposite from PVDF and (Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3

Thin films of some polymer–ceramics multiferroic nanocomposites (in 0–3 connectivity) of compositions (1 − x)PVDF–x((Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3 (x = 0.05,0.1,0.15)) have been prepared using a standard solution casting method. The basic structure and surface morphology of the materials were studied using X-ray diffraction and scanning electron microscopy technique respectively. Structural investigation confirms the presence of polymeric electro active β-phase of matrix (PVDF) and nano filler perovskite phase of the incorporated nano-ceramics. The high resolution transmission electron micrograph of the prepared nano-ceramic thin film composite has shown distinct and uniformly distributed particles (with less agglomeration). This has been observed in SEM micrographs also. The flexible nano-composites fabricated with polymer (PVDF), bismuth ferrite (BiFeO3) and ferroelectric (BST) exhibit high dielectric constant and low tangent loss. The electric response investigated by impedance spectroscopy technique in terms of electric circuit has provided some interesting results on contributions of grain and grain boundary in the restive characteristics of the composites. The study of ac conductivity as a function of frequency obeys Jonscher’s power law. The experimentally obtained first order magnetoelectric coefficient (αME) is found to encouraging for multifunctional application. The improved conductivity and dielectric properties suggest some promising applications in the embedded capacitors.

Various properties of the 0.6BaTiO 3 –0.4Ni 0 . 5 Zn 0 . 5 Fe 2 O 4 multiferroic nanocomposite

Structural, magnetic and ferroelectric properties of 0.6BaTiO3–0.4(Ni0.5Zn0.5Fe2O4) multiferroic nanocomposite are presented here. The structural properties of the samples were studied by XRD and Raman spectroscopy which confirm the formation of BaTiO3 (BTO) phase with a tetragonal perovskite structure and a small secondary spinel phase due to the ferrite content. The magnetic and electric orderings were investigated by vibrating sample magnetometer (VSM) and ferroelectric (P–E) loop tracer at room temperature. The inception of ferroelectric properties is due to barium titanate. The remnant polarization increases ∼5 times for the composite with Ni0.5Zn0.5Fe2O4 (NZFO) substitution compared to BTO. The remnant polarization is conducive for switching applications of multiferroic composite.

Synthesis and characterization of low density polyethylene with multiferroic bismuth ferrite nanocomposite

A novel low density polyethylene (LDPE) with multiferroic bismuth ferrite (BiFeO3) nano-dielectric was successfully prepared via a solution-melt blending method. The structure, thermal, magnetic, as well as dielectric properties of the nano-dielectric were examined. The microstructures of LDPE/BiFeO3 were characterized by Fourier transform infrared, X-ray diffraction, and scanning electron microscopy. Microstructural analysis indicated that BiFeO3 nanoparticles were well dispersed in the LDPE matrix and the structure of LDPE was unchanged even after doping with BiFeO3 nanoparticles. The differential scanning calorimetry data of the thermal properties revealed that melting temperature has decreased and crystallinity has increased. The reason was that amount of nucleation agents was increased and crystal propagation rate was changed. The corresponding magnetic and dielectric properties were measured using vibrating sample magnetometer and broadband dielectric spectrometer. The results showed that the magnetization behaviour of diamagnetic LDPE was transformed due to the antiferromagnetism of BiFeO3. In addition, the dielectric permittivity and loss of LDPE/BiFeO3 increased with increasing BiFeO3 filler concentrations in the LDPE matrix due to different response mechanisms.

Magnetoelectric polymer nanocomposite for flexible electronics

This paper reports the fabrication and characterization of a new type of magnetoelectric polymer nanocomposite that exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature. The multiferroic nanocomposite consists of high aspect ratio ferromagnetic iron nanowires embedded inside a ferroelectric co-polymer poly(vinylindene fluoride-trifluoroethylene), P(VDF-TrFE). The nanocomposite has been fabricated via a simple low temperature spin coating technique. Structural, ferromagnetic, ferroelectric, and magnetoelectric properties of the developed nanocomposite have been characterized. The nanocomposite films showed isotropic magnetic properties due to the random orientation of the iron nanowires inside the film. In addition, the embedded nanowires did not hinder the ferroelectric phase development of the nanocomposite. The developed nanocomposite showed a high magnetoelectric coupling response of 156 mV/cmOe measured at 3.1 kOe DC bias field. This value is among the highest reported magnetoelectric coupling in two phase particulate polymer nanocomposites.

Fabrication and Properties of Multiferroic Nanocomposite Films

A new type of multiferroic polymer nanocomposite is presented, which exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature. The multiferroic nanocomposite consists of a ferroelectric copolymer poly(vinylindene fluoride-trifluoroethylene) [P(VDF-TrFE)] and high aspect ratio ferromagnetic nickel (Ni) nanowires (NWs), which were grown inside anodic aluminum oxide membranes. The fabrication of nanocomposite films with Ni NWs embedded in P(VDF-TrFE) has been successfully carried out via a simple low-temperature spin-coating technique. Structural, ferromagnetic, and ferroelectric properties of the developed nanocomposite have been investigated. The remanent and saturation polarization as well as the coercive field of the ferroelectric phase are slightly affected by the incorporation of the NWs as well as the thickness of the films. While the former two decrease, the last increases by adding the NWs or increasing the thickness. The ferromagnetic properties of the nanocomposite films are found to be isotropic.

Adjustable magnetoelectric effect of self-assembled vertical multiferroic nanocomposite films by the in-plane misfit strain and ferromagnetic volume fraction

The strain-mediated magnetoelectric (ME) property of self-assembled vertical multiferroic nanocomposite films epitaxially grown on cubic substrates was calculated by a nonlinear thermodynamic theory combined with the elastic theory. The dependent relations of phase state of ferroelectric films with the in-plane misfit strain, out-of-plane misfit strain, temperature, and volume fraction of ferromagnetic phase were confirmed. The effects of in-plane misfit strain and ferromagnetic volume fraction on the polarization and dielectric constant of ferroelectric films at room temperature were elaborately analyzed for the vertical BaTiO3-CoFe2O4 and PbTiO3-CoFe2O4 nanocomposite films. Our calculated results confirmed the relationship among ME effect and in-plane misfit strain and ferromagnetic volume fraction in the nanocomposite films. The ME voltage coefficients of vertical BaTiO3-CoFe2O4 and PbTiO3-CoFe2O4 nanocomposite films displayed various maximums and abrupt points at special phases and phase transition boundaries. The ME voltage coefficients of lead-free BaTiO3-CoFe2O4 nanocomposite films epitaxially grown on different substrates could reach a comparative value of ∼2 V·cm−1·Oe−1 under the controllable in-plane misfit strain induced by substrate clamping. Our results provided an available method for the optimal design of vertical multiferroic nanocomposites with adjustable ME effect by optimizing the ferromagnetic volume fraction and substrate type.

Thin Film Multiferroic Nanocomposites by Ion Implantation

Thin film multiferroic nanocomposites might enable a range of potentially disruptive integrated magnetoelectric devices for information storage, spintronics, microwave telecommunications, and magnetic sensing. With this aim, we have investigated ion implantation of magnetic species into ferroelectric single crystal targets as a radically novel approach to prepare film nanoparticulate magnetic-metal ferroelectric-oxide composites. These materials are an alternative to multiferroic oxide epitaxial columnar nanostructures that are under intensive research, but whose magnetoelectric response is far from expectations. Here, we unambiguously demonstrate the preparation of such a thin film multiferroic nanocomposite of Co and BaTiO3 by ion implantation of a high dose of the magnetic species, followed by rapid thermal processing under tailored conditions. Results thus constitute a proof of concept for the feasibility of obtaining the materials by this alternative approach. Ion implantation is a standard technique for the microelectronic industry in combination with well-established patterning procedures.

Advanced imaging techniques for characterization of 0.5BaTiO3/0.5Ni0.5Zn0.5Fe2O4 multiferroic nanocomposite

New techniques are used to synthesis and characterize 0.5BaTiO3/0.5Ni0.5Zn0.5Fe2O4; (BTO/NZF) multiferroic nanocomposite. Improved citrate autocombustion preparation technique is used to synthesis ferromagnetic and ferroelectric phases of the investigated nanocomposite. Atomic force microscope (AFM) is one of the important tools for imaging, measuring, and manipulating matter at the nanoscale. AFM is used at different sample areas to confirm the data obtained from scanning electron microscope (SEM) and transmission electron microscope (TEM). Moreover AFM gives 3D visualization for the surface texture and roughness showing the morphology of the two distinguishes phases. The traditional characterizations techniques have been used such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) to identify the formation of the two individual phases separately and to study the chemical composition of the prepared nanocomposite respectively.

Preparation and Studies on (1-x) BiFeO3–x Li0.5Fe2.5O4 (x=0.25 And 0.5) multiferroic nano-composites

Multiferroic nano-composite (1-x) BiFeO3–x Li0.5Fe2.5O4 (x=0.25 and 0.5) have been successfully synthesized by mixing the two phases, prepared independently by two different methods followed by annealing at 600 0 C. Existence of the two phases in the composite is confirmed by x-ray diffraction pattern. Average particle size is calculated to be about 45 nm for both of these phases. The saturation magnetization, remnant magnetization and coercive field increases linearly with increasing ferromagnetic phase (Li0.5Fe2.5O4) as investigated by VSM measurement. Local magnetic behaviors have been investigated by 57 Fe Mossbauer spectroscopic studies. Large dielectric constant of the order of 10 3 -10 4 has been observed in these composites. Copyright © 2013 VBRI press

Enhancement of magnetoelectric effect in multiferroic fibrous nanocomposites via size-dependent material properties

We investigate the effective material properties of a multiferroic fibrous nanocomposite with size effects along its interface. The closed-form expression of the effective moduli of the nanocomposite shows that its response with interface effects depends on the size of the embedded fibers in the composite, a phenomenon different from the result based on the classical theory. We further demonstrate that the magnetoelectric effect can be substantially enhanced via proper design of the interface, providing an alternative avenue for controlling and, in particularly, increasing the magnetoelectric effect.

Microstructure and phase control in Bi–Fe–O multiferroic nanocomposite thin films

We report on the controlled multiphase thin film growth in the Bi–Fe–O system. By varying the deposition oxygen pressure, the dominant phase formed in the film continuously changes from ferroelectric BiFeO3 to a mixture of α-Fe2O3 and ferromagnetic γ-Fe2O3. X-ray diffraction and high-resolution transmission electron microscopy have revealed that epitaxial multiferroic nanocomposites consisting of BiFeO3 and Fe2O3 are formed when the deposition pressure is ≈5mTorr. In order to investigate the previously reported anomalous enhancement in magnetization in BiFeO3, we have fabricated a thickness gradient pure BiFeO3 film. The out-of-plane lattice constant was found to increase continuously as the thickness is decreased from 300 to 5nm, but no significant enhancement in magnetization was observed.

A least-squares spectral curve fitting routine for strongly overlapping Lorentzians or Gaussians

A new multiferroic nanocomposite resulting from a subtile mixture of Ni0.5Zn0.5Fe2O4 and TiO2 nanocrystalline grains was synthesized by bottom-up approach. The structural, nanostructural and morphological characteristics of the nanocomposite were carefully evaluated from the X-ray patterns, from fringe patterns and selected area electron diffraction (SAED) patterns obtained by High Resolution Transmission Electron Microscope. The dielectric permittivity of the NZFO-TO nanocomposite is characterized by a phase transition from the ferroelectric to paraelectric order at ∼390 K while the corresponding spectrum reveals a non-Debye type of relaxation phenomenon. It is concluded that this nanocomposite is suitable to be applied in magnetoelectric devices.