Direct Magnetoelectric Coupling Research Articles

Large room temperature magnetoelectric response in quasi 1–2 nanocomposite films on mica substrate

AbstractA novel quasi 1–2 type magnetoelectric (ME) nanocomposite films composted of one‐dimensional CoFe2O4 nanofibers and two‐dimensional PbZr0.2Ti0.8O3 films on flexible mica substrate have been designed and fabricated. The ME coupling effects have been greatly enhanced due to the release of the clamping effect and the high strain transfer efficiency between the large aspect ratio of the nanofibers and ferroelectric thin films. The release of the clamping effect was confirmed by reducing the thickness of the mica substrate, in which the piezoelectric coefficient and ME coupling coefficient of the nanocomposite films have been greatly boosted by the decrease in the mica thickness. A large direct ME coupling coefficient of 630 mV/(cm Oe) and a converse ME coupling coefficient of 1.43 × 10−8 s/m have been achieved in the quasi 1–2 nanocomposite film with a substrate thickness of 25 µm. Furthermore, the stain‐mediated ME coupling was revealed by magnetic field/electric field‐induced local ferroelectric/magnetic domain switching dynamics.

Phosphate bonded CoFe2O4–BaTiO3 layered structures: Dielectric relaxations and magnetoelectric coupling

Multilayered phosphate bonded CoFe2O4–BaTiO3–CoFe2O4 (CBC) and BaTiO3–CoFe2O4–BaTiO3 (BCB) multiferroic structures were formed by means of uniaxial pressing. The dielectric properties were studied in 20 Hz – 1 GHz frequency and 120–500 K temperature ranges. The complex dielectric permittivity is 15–0.17i for CBC and 22–0.04i for BCB, it is temperature- and frequency-independent below 250 K. At higher temperatures, strong dispersion appeared governed by the Maxwell–Wagner relaxation. Such behaviour is determined by the 2–2 connectivity of the sample. The highest direct magnetoelectric coupling coefficient was found for the BaTiO3–CoFe2O4–BaTiO3 structure of 0.2 mVOe–1cm–1.

Magnetodielectric and TMR effects in P(VDF-HFP)/SrFe12O19 composite films for magnetic field – Tuned photodetector application

Magnetoelectric (ME) multiferroic materials possess extensive research interest as a result of their use in a variety of sectors. In this work, the optical properties of plain P(VDF-HFP) film and P(VDF-HFP)/SrFe12O19 composite films are investigated through UV-Vis absorption spectroscopy. In addition, the ME coupling of SrFe12O19 nanofibers reinforced P(VDF-HFP) composite films is investigated though magnetodielectric (MD) measurements. The parameters such as dielectric constant, capacitance, dielectric loss and impedance of the composite films are found to change with the applied magnetic field which is attributed to the direct ME coupling of the composite films. The prepared ME films show a negative tunneling magnetoresistance (TMR) effect with maximum TMR% of 14 % for the film (PSNF20) with 20 wt% of SrFe12O19 nanofiber loading. Photodetectors are fabricated using the films as active elements and the performance of the photodetectors is studied under various intensities of visible light radiation. All the devices exhibit good photosensitivity, responsivity and specific detectivity at an illumination intensity of 20 mW/cm2. The photodetector (PD20) fabricated using PSNF20 as an active element has the maximum rise/decay time, photosensitivity, responsivity and specific detectivity values as 468 /553 ms, 2.7 × 103, 22 mA/W and 6.77 × 1013 Jones, respectively at 20 mW/cm2. In addition, the performance of the devices is analyzed by subjecting the active element to external magnetic field. The photosensitivity, responsivity and specific detectivity all improve, showing that the magnetic field has an effect on the photodetector. The above parameters are maximum for PD20 device and the values are 4.3 × 103, 26 mA/W and, 8.01 × 1013 Jones, respectively at 4000 Oe and 20 mW/cm2. Thus, the prepared flexible magnetoelectric films of P(VDF-HFP)/SrFe12O19 nanofiber composites have been shown to be good options for the magnetic field tuned photodetector applications such as environmental sensing monitor, safety and security, optical communication systems, magnetic sensors, piezoelectric sensors and spintronics devices.

Magnetoelectric coupling in nonsintered bulk BaTiO3 -- xCoFe2O4 multiferroic composites

Bulk BaTiO3-xCoFe2O4, x = 0.1 – 0.6 magnetoelectric composites were prepared using the phosphate bonded ceramics approach. XRD analysis proved the purity of both phases. The dielectric properties are governed by a series of composition-dependent Maxwell-Wagner relaxations and conductivity at lower frequencies and a phase transition-related anomaly at higher frequencies. A dielectric constant as high as 616 – 9387i is observed at 500 K for BaTiO3-0.6CoFe2O4. The magnetic hysteresis demonstrates a high Ms/Mr ratio of 0.46, which is related to the around 30 nm size of the CoFe2O4 particles. The measured direct magnetoelectric coupling coefficient of 1.1 mV Oe−1 cm−1 is higher than that of the conventionally sintered ceramics and compatible with that of core-shell structures.

The involvement of Pna21 phase in the multiferroic characteristics of La/Lu co-substituted BiFeO3 ceramics

Rare earth ion (RE)-substitution has been recognized as an effective way for improving multiferroic properties especially for realizing the electric field-controlled magnetism in BiFeO3 ceramics, where the symmetry modulation of R3c-Pna21-Pbnm and unlocking ferromagnetism by destroying the cycloidal spin structure are the key points. In Lu-substituted BiFeO3 ceramics, however, the Pna21 phase is not involved. In the present work, La/Lu co-substitution was investigated to involve the Pna21 phase in BiFeO3 ceramics. The phase transition from R3c to Pna21 occurred with an increase in x, and the mixed structure of R3c, Pna21, and Pbnm phases was determined in Bi0.82−xLaxLu0.18FeO3 ceramics. The greatly enhanced ferroelectric polarization and the switching from antiferromagnetic to the weak ferromagnetic state through the destruction of the cycloidal spin structure were achieved. Subsequently, the direct magnetoelectric coupling coefficient αME up to 2.02 mV/cm Oe was obtained. The increased effective ionic radius of RE in the present ceramics played a key role in involving Pna21 phase in RE-substituted BiFeO3 ceramics, and the critical value was about 0.104 23(2) nm.

Demagnetization Effect on the Magnetoelectric Response of Composite Multiferroic Cylinders

Strain-mediated multiferroic composite structures are gaining scientific and technological attention because of the promise of low power consumption and greater flexibility in material and geometry choices. In this study, the direct magnetoelectric coupling coefficient (DME) of composite multiferroic cylinders, consisting of two mechanically bonded concentric cylinders, was analytically modeled under the influence of a radially emanating magnetic field. The analysis framework emphasized the effect of demagnetization on the overall performance. The demagnetization effect was thoroughly considered as a function of the imposed mechanical boundary conditions, the geometrical dimensions of the composite cylinder, and the introduction of a thin elastic layer at the interface between the inner piezomagnetic and outer piezoelectric cylinders. The results indicate that the demagnetization effect adversely impacted the DME coefficient. In a trial to compensate for the reduction in peak DME coefficient due to demagnetization, a non-dimensional geometrical analysis was carried out to identify the geometrical attributes corresponding to the maximum DME. It was observed that the peak DME coefficient was nearly unaffected by varying the inner radius of the composite cylinder, while it approached its maximum value when the thickness of the piezoelectric cylinder was almost 60% of the total thickness of the composite cylinder. The latter conclusion was true for all of the considered boundary conditions.

Magnetoelectric Coupling Triggered by Noncollinear Magnetic Structure in M‐Type Hexaferrite

AbstractDirect magnetoelectric (ME) coupling between magnetic and ferroelectric orders, which can be realized in spiral magnets, is vital in technological applications of multifunctional materials. Multisusceptible BaFe12O19 is noteworthy for its excellent magnetic, dielectric properties and thus the application in high‐density information storage, while its collinear spin structure limits the emergence of ferroelectrics and ME coupling. In this work, nonzero Dzyaloshinskii–Moriya (DM) interaction is created by partial substitution of the spin‐down Fe3+ sites to induce conical spin structure in BaFe12O19. Larger In3+ ions are introduced and prefer to occupy the spin‐down 4f1 and 4f2 lattice sites. The evolution of magnetization versus temperature adduces evidence of conical magnetic structure. As a result, direct ME and magnetodielectric coupling are obtained in In‐doped BaFe12O19 ceramics. An interlayer DM interaction model is built to discuss the intrinsic relationship among crystal structure, noncollinear magnetic structure, and ionic substitution. Moreover, BaZn0.9Zr0.9Fe10.2O19 ceramics are also prepared, and exhibit noncollinear magnetic structure and direct ME coupling since Zn2+ and Zr4+ also possess larger radii than Fe3+ and prefer to enter the spin‐down sites. The present result provides a feasible avenue to develop multiferroic and magnetoelectric coupling in ubiquitous M‐type hexaferrite.

New approach for designing bulk multiferroic composites made of two perovskite oxides with enhanced direct magnetoelectric coupling

The scarcity of single-phase magnetoelectric multiferroics has motivated active research towards the design of composites where polarization and magnetization are coupled through elastic strain at their interfaces. Up to now, most of bulk multiferroic composites are made of immiscible constituents that thus suffer from weak interface connectivity between them. Here, we propose an approach for designing particulate composites with constituents of perovskite ABO3 structure that exhibit solid solubility, by acting on the lowering of the sintering temperature. We show that a BiFe0.95Co0.05O3–PbZr0.52Ti0.48O3 multiferroic composite with improved magnetoelectric coupling can be formed before a solid solution is reached. A Bi-rich interface promotes elastic strain transfer between the two constituents resulting in twice stronger direct magnetoelectric coefficient compared to pure BiFe0.95Co0.05O3. These findings provide an easy and effective strategy for producing upgraded and original multiferroic composites made of constituents with the perovskite structure, known to host a wide variety of functionalities.

Room temperature magnetoelectric coupling in Fe-doped sodium bismuth titanate ceramics

Multiferroic ceramics with switchable magnetization as well as high polarization at room temperature have remarkable technological impact. Herein, we report that a small concentration of Fe doping in the B-site of sodium bismuth titanate (NBT) lead to room temperature multiferroic nature with fascinating properties. The key factor responsible for the embellished multiferroic behavior at room temperature was electric field induced non-180° domain alignment bridged with dynamic exchange interaction of trapped electrons in ordered polarons. The optimum doping of 0.02 mole fractions Fe in NBT favored ferromagnetic loop with highest remanence of 198 memu/g and coercive field 133 Oe along with improved ferroelectric polarization of 31.8 μC/cm2 and a strong self-biased direct magnetoelectric coupling coefficient of 7.38 mV/cmOe. Strong coupling at low ac field, high reliability, easy control by an electric signal and fast switching behavior add importance to this lead-free Fe-doped sodium bismuth titanate ceramic as potential material, applicable in biocompatible magnetic sensors.

Engineering Resonance Modes for Enhanced Magnetoelectric Coupling in Bilayer Laminate Composites for Energy Harvesting Applications

The magnetoelectric (ME) effect in composites, a strain-mediated coupling phenomenon between piezoelectric and magnetostrictive phases, has a wide range of technological applications. Here, ME coupling phenomena are explored in $\mathrm{Pb}$-free piezoelectric, $0.5\mathrm{Ba}({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}){\mathrm{O}}_{3}\text{\ensuremath{-}}0.5({\mathrm{Ba}}_{0.7}{\mathrm{Ca}}_{0.3}){\mathrm{Ti}\mathrm{O}}_{3}$ and piezomagnetic ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ bilayer laminate composites. The direct and converse ME coupling strengths are found to be enhanced at the electromechanical resonance modes, rather than at the off-resonance frequencies. Here, it is proposed to further enhance the ME coupling strength at electromechanical resonance modes by the in-phase superimposition of the radial and second bending modes via varying the bilayer thickness, which, in turn, varies the volume fraction of the bilayer. The proposed enhanced ME coupling is experimentally demonstrated at a theoretically envisaged bilayer thickness of about 1.8 mm. This results in a large direct ME coupling coefficient of $22.5\phantom{\rule{0.1em}{0ex}}\mathrm{V}\phantom{\rule{0.1em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}\mathrm{O}{\mathrm{e}}^{\ensuremath{-}1}$, which is around 100% more than the values observed at individual resonance modes. The results are further validated by calculations from theoretical models. The method adopted in this work gives a roadmap to the significant enhancement of the ME effect in laminate composites.

Anomalous Magnetoelectric Coupling Effect of CoFe2O4–BaTiO3 Binary Mixed Fluids

We report an anomalous magnetoelectric coupling effect of CoFe2O4–BaTiO3 binary mixed fluids, which were prepared by distributing surfactant treated (oleic acid) magnetic CoFe2O4 and ferroelectric BaTiO3 nanoparticles into highly insulating base fluid (silicone oil). A strong coupling effect in this mixed fluid has been observed, in which both the remnant polarization/magnetization and coercive electric/magnetic field are found to be enhanced visibly in the presence of an external magnetic/electric field. Colossal converse and direct magnetoelectric coupling coefficients are estimated to be αH = 1.22 × 10–4Oe·cm/V and αE = 2.52 × 104 V/(cm·Oe), respectively. Moreover, this coefficient clearly depends on the volume fraction of the two kinds of particles and the applied external magnetic/electric field. Even more amazing, CoFe2O4 also shows a strong magnetoelectric coupling effect with a coefficient as high as 4.2 × 10–5 Oe·cm/V. Further analysis indicates that the aggregated, chain-like structure of the pa...

Tailoring the magnetic properties of cobalt ferrite nanoparticles using the polyol process.

Background: In extrinsically magnetoelectric materials made of two components, the direct magnetoelectric coupling arises from a mechanical strain transmission at the interface due to the shape change of the magnetostrictive component under an external magnetic field. Here, the size of the interface between the two components plays a crucial role. Therefore, the development of nanomaterials exhibiting large surface-to-volume ratios can help to respond to such a requirement. However, the magnetic nanoparticles (NPs) must be highly magnetostrictive and magnetically blocked at room temperature despite their nanometer-size. We describe here the use of the polyol process to synthesize cobalt ferrite (CoxFe3−xO4) nanoparticles with controlled size and composition and the study of the relationship between size and composition and the magnetic behavior.Methods: We used an improved synthesis of magnetostrictive CoxFe3−xO4 NPs based on the forced hydrolysis of metallic salts in a polyol solvent, varying the fraction x. Stoichiometric NPs (x = 1) are expected to be highly magnetostrictive while the sub-stoichiometric NPs (particularly for x ≈ 0.7) are expected to be less magnetostrictive but to present a higher magnetocrystalline anisotropy constant, as previously observed in bulk cobalt ferrites. To control the size of the NPs, in order to overcome the superparamagnetic limit, as well as their chemical composition, in order to get the desired magnetomechanic properties, we carried out the reactions for two nominal precursor contents (x = 1 and 0.67), using two different solvents, i.e., triethylene glycol (TriEG) and tetraethylene glycol (TetEG), and three different durations of refluxing (3, 6 and 15 h). The structure, microstructure and composition of the resulting NPs were then investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray fluorescence spectroscopy (XRF), respectively. The magnetic properties were also evaluated using standard magnetometry. To measure the magnetostrictive response of the particles, the particles were sintered to dense pellets on which strain gauges were bonded, measuring the size variation radially, as a function of a dc magnetic field.Findings: We found two samples, the first one being stoichiometric and magnetostrictive, and the second one being sub-stoichiometric and presenting a higher magnetization, that are appropriate to be used as ferromagnetic building blocks in nanostructured magnetoelectric materials, particularly materials based on polymers. We show that the polyol solvent and the reaction time are two key parameters to control the size and the magnetic properties of the resulting nanoparticles. We believe that these results provide relevant insights to the design of efficient magnetic and magnetostrictive nanoparticles that can be further functionalized by coupling agents, to be contacted with piezoelectric polymers.

Tunability of Bandgap and Magnetism in K and Pb Codoped BiFeO3 Nanoparticles for Multiferroic Applications: The Role of Structural Transition and Fe Deficiency

BiFeO3 is the most well-known single-phase material for multiferroic and photovoltaic applications because of its large ferroelectric polarization and high operating temperature. However, direct magnetoelectric coupling between ferroelectricity and magnetic order in bulk BiFeO3 is exceedingly weak, resulting from its intrinsic cycloidal spin structure. Fortunately, nanostructured BiFeO3 could exhibit multiferroism due to superficial uncompensated spins, thereby altering the magnetic order of the bulk phase. Here, the optical property and magnetism of Bi1–x(KPb)xFeO3 (0 ≤ x ≤ 0.1) nanoparticles are studied. X-ray powder diffraction and Raman spectroscopy reveal the apparent increase of cubic crystal phase (Pm-3m) and the emergence of Fe deficiency with the increase of K and Pb codoping content in BiFeO3 nanoparticles. Fe deficiency and its change in Bi1–x(KPb)xFeO3 nanoparticles are further confirmed by EDX and XPS spectra, besides the presence of Bi3+, Fe3+, and Pb4+ ions. The optical bandgap is narrowed gradually in the samples with the increase of K and Pb codoping content, and the corresponding phenomenological model is proposed. Magnetic hysteresis and magnetization versus temperature curves indicate the coexistence of antiferromagnetic and ferromagnetic orderings in Bi1–x(KPb)xFeO3 nanoparticles. The saturation magnetization first decreases and then increases with K and Pb codoping concentration increasing. A correlation among the structural transition, Fe deficiency, and magnetic property has been established in detail, which provides a possibility to further understand the cycloidal spin magnetic structure of BiFeO3 and improve its magnetic property for multiferroic applications.

Magnetoelectric coupling in strained strontium titanate and Metglas based magnetoelectric trilayer

Direct magneto electric coupling is observed with a magnetoelectric coupling coefficient (MECC) of 806 mV cm−1 Oe−1 at 750 Hz in strontium titanate (STO) - Metglas - strontium titanate (STO-Metglas-STO) trilayer thin films with a total thickness of 600 nm. The piezoelectricity in the strained STO layer, which is otherwise a paraelectric material, enabled the sandwiched magneto electric structure to exhibit a fair sub resonant magneto electric coupling. Theoretical models proposed by Bichurin et al. and Hasanyan et al. are employed to calculate the values of MECC at sub resonant condition for the system, which is noted as 853 mV cm−1 Oe−1. The frequency dependence of MECC coefficient is also calculated and the resonance frequency is estimated as 706 Hz.

Magnetic Field Sensors Based on the Direct Magneto-Electric Effect in Hexaferrite Thin Films and the Equivalent Circuit Model

We propose the design, fabrication, experimental implementation, and equivalent circuit model of a magneto-electric (ME) sensing device for determining the magnitude and direction of low-frequency ac magnetic fields. The device consists of two capacitive ME thin-film sensors fabricated by means of the laser ablation technique inside a pulsed laser deposition (PLD) chamber. The films are grown on a 500-nm thick indium tin oxide layer on $1.5\times 1.5$ cm2 silicon substrates using two deposition methods, namely, single target (ST) and multiple target (MT). The proposed setup is used to detect ac magnetic fields generated from a solenoid coil located at a distance of 10 mm. The experimental results demonstrate that the proposed magnetic field sensing approach using the MT method can establish the magnitude and direction of external magnetic fields with detection errors below 8%. Based on the experimental observations, we also establish a mathematical expression describing the direct ME coupling effect observed in M-type strontium hexaferrite thin films. Subsequently, we develop an electrical circuit model that can accurately predict device behavior using circuit simulations. The differential output voltages at different field strengths are predicted for both ST and MT films by simulating this equivalent circuit using the LTspice software from Linear Technology. The simulation results are in good agreement with the experimental data both qualitatively and quantitatively, and the average difference between the two ranges from 5% to 19% in the worst case.

A comparative study on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 composite ceramics

High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the structural, dielectric and multiferroic properties of Co0.6Cu0.3Zn0.1Fe2O4/Ba0.9Sr0.1Zr0.1Ti0.9O3 (CCZFO/BSZTO) composite ceramics prepared by sol-gel method. The XRD results confirm successful formation of the CCZFO/BSZTO composites without presence of any impurity phase. The mean grain size is about 1.5 mm and it shows double dispersing behavior, the larger grains belong to CCZFO while the smaller ones are ascribed to BSZTO. The maximum dielectric constant and loss appear with the molar ratio is 1:1 due to its more grain boundaries. Two peaks appear in the ε∼T curves, the peak corresponding to the lower temperature corresponds to the Curie temperature of BSZTO, while the other one is resulted by the relaxation polarization. The height of the relaxation peak decreases and the position shifts to higher temperature range with the increase of molar ratio. The maximal remanent polarization is 3.76 μC/cm2, obtained at 1 kHz when the molar ratio is 1:1. An enhanced magnetic properties are observed when the molar ratio is 1:1 due to the stronger interface interaction effect between the two phases. Strong direct magnetoelectric coupling coefficient of 1.53 V/(cm.Oe) is obtained at the field of 8000 Oe for the sample 1:4. These results may provide valuable information for improving the multiferroic properties of composite multiferroic materials.

Large modulation of perpendicular magnetic anisotropy in a BiFeO3/Al2O3/Pt/Co/Pt multiferroic heterostructure via spontaneous polarizations

Magnetism control has a variety of applications in magnetic storage and spintronic devices. Instead of the control of direct magnetoelectric coupling via strain, voltage, and Dzyaloshinskii-Moriya interaction, the polarization-dependent coupling in multiferroic materials such as BiFeO3 is employed for the electric-field control of magnetizations in this work. A perpendicular magnetic anisotropy (PMA) has been realized in a BiFeO3/Al2O3/Pt/Co/Pt multiferroic structure at room temperature. Interestingly, a distinct change of coercivity field (∼400%) has been observed in the structure with opposite polarization directions, which can be attributed to the different oxidation degree at the Pt/Co interface. This spontaneous polarization-controlled switching not only provides us a platform to study the interfacial effect in multiferroic heterostructures but also paves the way to manipulate PMA or even spin orbit torque through oxygen vacancies.

Influence of composition ratio on ferroelectric, magnetic and magnetoelectric properties of PMN–PT/CFO composite thin films

Multiferroic 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3/CoFe2O4 (PMN–PT/CFO) composite films have been grown on Pt/Ti/SiO2/Si substrate via sol–gel spin-coating technique. PMN–PT and CFO precursor solutions were mixed before the spin-coating process to optimize the interface interaction. We investigated the influence of the composition ratio and annealing process on the property of the multiferroic PMN–PT/CFO composite films. The films which entirely consist of PMN–PT and CFO phases have a good performance in the ferroelectric, ferromagnetic property and direct magnetoelectric coupling effect when they were annealed at 730 °C and air atmosphere. It was obviously noticed that the composition ratio between PMN–PT and CFO has an effect on the properties of PMN–PT/CFO multiferroic composites.

Strong magnetoelectric coupling effect in BaTiO3@CoFe2O4 magnetoelectric multiferroic fluids.

Magnetoelectric multiferroic fluids composed of BaTiO3@CoFe2O4 composite nanoparticles dispersed in a highly insulating nonpolar oleic acid/silicone oil mixture have been developed. The effects of the particle volume fraction and a magnetic field, as well as an electric field, on the ferroelectric and magnetic properties, as well as the magnetoelectric coupling effect, have been systematically studied and discussed in this paper. Magnetic characterization shows an approximation to superparamagnetism, and both the remanent magnetization (Mr) and the coercive field (Hc) increase with increases in the volume fraction and applied electric field. Similarly, a superparaelectric state has been observed in the multiferroic fluids, in which both the remanent polarization (Pr) and the coercive field (Ec) are near zero, whereas they increase with increases in the applied magnetic field and volume fraction. High converse and direct magnetoelectric coupling coefficients are estimated to be αH = 8.16 × 10-4 (Oe cm) V-1 and αE = 1.58 × 104 V (cm Oe)-1, respectively. Further analysis indicates that the composite particles can be aligned under an external magnetic/electric field so that their magnetic/electric moments can be parallel to the external field, which in turn results in changes in the magnetization/polarization directions. These results imply that besides magnetoelectric fluids that consist of core/shell-structured nanoparticles, conventional multiferroic fluids based on composite particles may provide an opportunity to gain electrical control of magnetization and vice versa, which implies potential applications.

Anomalous Nonlocal Resistance and Spin-Charge Conversion Mechanisms in Two-Dimensional Metals.

We uncover two anomalous features in the nonlocal transport behavior of two-dimensional metallic materials with spin-orbit coupling. First, the nonlocal resistance can have negative values and oscillate with distance, even in the absence of a magnetic field. Second, the oscillations of the nonlocal resistance under an applied in-plane magnetic field (the Hanle effect) can be asymmetric under field reversal. Both features are produced by direct magnetoelectric coupling, which is possible in materials with broken inversion symmetry but was not included in previous spin-diffusion theories of nonlocal transport. These effects can be used to identify the relative contributions of different spin-charge conversion mechanisms. They should be observable in adatom-functionalized graphene, and they may provide the reason for discrepancies in recent nonlocal transport experiments on graphene.