Magnetic Sensor Applications Research Articles

Multifunctional solution blow spun NiFe–NiFe2O4 composite nanofibers: Structure, magnetic properties and OER activity

Multifunctional nanomaterials are of great technological interest due to a wide range of applications. This study reports the structure, magnetic properties and electrocatalytic activity to oxygen evolution reaction (OER) of NiFe–NiFe2O4 composite nanofibers prepared by solution blow spinning (SBS) with an average diameter of 133.4 nm. X-ray diffraction (XRD) analysis revealed that NiFe alloy crystallites have an average size of 26.3 nm. The magnetization versus temperature (MxT) and magnetization versus magnetic field (MxH) measurements show saturation magnetization of 123 emu g−1 and thermal blocking temperature of 117 K. The MxT measurements show a quick response of the composite sample to magnetic field variations of ±0.3 Oe, indicating that the solution blow spun material has great potential for magnetic sensor applications. From an electrocatalytic point of view, nanofibers show a low overpotential of 316 mV vs RHE at J = 10 mA cm−2, and a significant turnover frequency (TOF) of 4.03 s−1 at only 400 mV. NiFe–NiFe2O4 nanofibers have an excellent chemical stability as revealed by chronopotentiometry analysis along 15 h. These results stand solution blow spun NiFe–NiFe2O4 composite nanofibers in line with the best NiFe-based catalysts reported in the literature.

Structural, magnetic and ferroelectric properties of lead free piezoelectric 0.9(0.45Ba0.7Ca0.3TiO3-0.55BaTi0.8Zr0.2O3) and magnetostrictive 0.1(Co0.7Mn0.3Fe1.95Dy0.05O4) magnetoelectric particulate composite

The structural, magnetic, ferroelectric, and magnetoelectric (ME) properties of lead-free ferroelectric phase (0.45)Ba0.7Ca0.3TiO3-(0.55)BaTi0.8Zr0.2O3 (BCZT) and rare earth modified Co-Mn ferrite phase Co0.7Mn0.3Fe1.95Dy0.05O4 (CMFDO) magnetoelectric (ME) composites are reported. X-ray diffraction confirms the presence of a crystal structure corresponding to both the ferroelectric and ferrite phases, which was further confirmed by Raman spectroscopic measurements. Scanning electron micrograph imaging along with the elemental mapping reveals the distribution of CMFDO grains in a BCZT matrix. The variation of dc resistivity with temperature indicates a semiconducting nature of the ME composite. The ME composite shows usual dielectric dispersion behavior with a higher dielectric constant value in the low frequency region compared to the individual ferroic phases, due to the space charge effects. Frequency dependent ac conductivity reveals that the conduction process in the ME composite is due to the small polaron hopping mechanism. Also, the variation of dielectric constant with temperature reveals the presence of two dielectric anomalies corresponding to ferroelectric phase transitions, i.e., from orthorhombic (O) to tetragonal (T) phases (∼298–323 K) and tetragonal (T) to cubic (C) phases (∼400 K). The ME composite exhibits both the ferroelectric [i.e., polarization (P) vs electric field (E)] and ferrimagnetic [i.e., magnetization (M) vs magnetic field (H)] hysteresis loops that confirm its multiferroic nature. The P-E hysteresis loop indicates the significant changes in remanent polarization (ΔPr ∼ 54%) after magnetic poling, confirming the presence of strong magnetoelectric coupling in the ME composite. Further, the strength of the ME coupling calculated was ∼54%, which is remarkable. Thus, the ME composite prepared in the present study may be a suitable candidate for applications in magnetic field sensors and multistate memory devices and may be suitable alternatives for single phase multiferroics.

Magnetization behavior of NiMnGa alloy nanowires prepared by DC electrodeposition

NiMnGa have potential applications for magnetic field sensors, strain sensors, actuators and solid-state refrigeration, due to their unique microstructures and crystalline phases at various temperatures. Synthesis of Heusler type NiMnGa nanowires (diameter ~200 nm) has been done by low cost DC electrodeposition method using AAO templates. This method was employed due to its cost effectiveness, simplicity, and precise control over composition, diameter and length of nanotubes/nanowires. It has been observed that Ga concentration decreases as Mn concentration increases with the rise in potential. Magnetic properties have been studied at room temperature as well as at low temperatures. It has been found that coercivity (Hc) increases as temperature decreases. The nanowires have maintained ferromagnetic behavior from 10 K to RT.

Controlling Magnetization of Gr/Ni Composite for Application in High-Performance Magnetic Sensors

Graphene (Gr), a well-known 2D material, has been under intensive investigation in the last decade due to its high potential applications in industry and advanced technological elements. The Gr, while composed with magnetic materials, has opened new opportunities for further developments of magnetic based devices. Here, we report a mass production of Gr/Ni composite powders using electrochemical exfoliation/deposition method with different magnetic strengths of the final composite material. We applied the magnetic composite materials in a magnetoimpedance (MI) based sensor and observed significant enhancement in the MI effect and its field sensitivity. Such magnetic composites with controlled magnetization strengths are coated on the MI-ribbon sensor surface and different MI responses are observed. The MI response of a ribbon coated with a Gr/Ni layer is theoretically determined based on an electrodynamic model with a qualitative consistency between the experimental results and the theoretical model. Our comprehensive study can be applied in high performance functionalized MI based magnetic sensors and devices.

Development of Magnetic Microwires for Magnetic Sensor Applications.

Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m), Giant Magneto-impedance effect, GMI, or rectangular hysteresis loops combined with quite fast domain wall, DW, propagation. In this paper we overview the magnetic properties of thin magnetic wires and post-processing allowing optimization of their magnetic properties for magnetic sensor applications. We concluded that the GMI effect, magnetic softness or DW dynamics of microwires can be tailored by controlling the magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and domain structure by appropriate thermal treatment.

Electric-field controlled magnetic reorientation in exchange coupled CoFeB/Ni bilayer microstructures

A novel strain-mediated composite multiferroic system is investigated in this work. The system is composed of magnetostrictive microstructures made of a ferromagnetic bilayer of negative magnetostrictive Ni and positive magnetostrictive CoFeB fabricated on a ferroelectric Pb(Mg1/3Nb2/3)0.69Ti0.31O3 (PMN-PT) single crystal substrate. When an electric field is applied across the PMN-PT substrate, magnetization reorientation occurs in the microstructures that are predominantly initialized into flux-closure states. An x-ray magnetic circular dichroism-photoemission electron microscope is used to experimentally visualize the electrically induced changes of the magnetization state of the individual layers as well as the exchange coupling between the two layers. Such heterostructures with tunable magnetoelectric properties have potential for new magnetic memory and sensor applications.

Magnetic Scattering in Ni Wires Fabricated on Ferroelectric LiNbO3 Substrate for Magnetic Sensor Application

Magnetic Scattering in Ni Wires Fabricated on Ferroelectric LiNbO3 Substrate for Magnetic Sensor Application

Huge local magnetic field enhancement at optical frequencies in metamaterials through coupling with photonic band gap

We theoretically study the coupling of magnetic plasmon polaritons (MPPs) with photonic band gap (PBG) in a system composed of a one-dimensional (1D) silver nanowire pair array lying on a one-dimensional photonic crystal (1D PC). The near-field plasmon interactions in individual silver nanowire pairs induce MPPs. The 1D PC consisting of dielectric multilayer stacks with alternating refractive indices forms a PBG in the reflection spectrum. When the position of the PBG of the 1D PC is tuned to be close to the MPPs, the MPPs and the PBG can couple together to lead to a hybrid mode within the PBG. At the hybrid mode resonance, the magnetic fields in the center of Ag nanowire pairs are enhanced to nearly 4.3 times larger than those in the nanowire pair array directly lying on a substrate. Our numerical results hold important applications in magnetic sensors and magnetic nonlinearity.

Surface-vacancy-induced metallicity and layer-dependent magnetic anisotropy energy in Cr2Ge2Te6

Two-dimensional van der Waals materials have attracted considerable attention because of their promising applications in spintronic devices. This paper reports on first-principles calculations of the electronic structure and ferromagnetism of Cr2Ge2Te6 with surface Ge vacancies. These vacancies are found to remove the bandgap and induce metallicity in Cr2Ge2Te6 that persists with decreasing Ge-vacancy concentration. Meanwhile, the Ge vacancies cause an unexpected sharp increase in the magnetic anisotropy energy compared to that of perfect Cr2Ge2Te6. More importantly, how thickness affects the magnetic anisotropy energy is studied to show that the latter oscillates upon increasing the number of layers, thereby switching between the out-of-plane and in-plane magnetization directions. The present findings regarding a surface-vacancy-tuned bandgap and magnetism controlled by the layer thickness in a two-dimensional van der Waals magnet could lead to potential applications in next-generation magnetic memory storage, sensors, and spintronics.

Manetoresistance of Ultralow-Hole-Density Monolayer Epitaxial Graphene Grown on SiC.

Silicon carbide (SiC) has already found useful applications in high-power electronic devices and light-emitting diodes (LEDs). Interestingly, SiC is a suitable substrate for growing monolayer epitaxial graphene and GaN-based devices. Therefore, it provides the opportunity for integration of high-power devices, LEDs, atomically thin electronics, and high-frequency devices, all of which can be prepared on the same SiC substrate. In this paper, we concentrate on detailed measurements on ultralow-density p-type monolayer epitaxial graphene, which has yet to be extensively studied. The measured resistivity ρxx shows insulating behavior in the sense that ρxx decreases with increasing temperature T over a wide range of T (1.5 K ≤ T ≤ 300 K). The crossover from negative magnetoresistivity (MR) to positive magnetoresistivity at T = 40 K in the low-field regime is ascribed to a transition from low-T quantum transport to high-T classical transport. For T ≥ 120 K, the measured positive MR ratio [ρxx(B) − ρxx(B = 0)]/ρxx(B = 0) at B = 2 T decreases with increasing T, but the positive MR persists up to room temperature. Our experimental results suggest that the large MR ratio (~100% at B = 9 T) is an intrinsic property of ultralow-charge-density graphene, regardless of the carrier type. This effect may find applications in magnetic sensors and magnetoresistance devices.

La0·7Ca0.3−xSrxMnO3:Ag0.2 (0.0165 ≤ x ≤ 0.1) ceramics with large and stable TCR in different magnetic field environments

La0·7Ca0.3−xSrxMnO3:Ag0.2 (LCSMO:Ag) ceramics with varying strontium (Sr) content (x = 0.0165, 0.03, 0.05, 0.07, and 0.1) were synthesized using a combination of sol–gel and solid-state doping methods and studied as colossal magnetoresistance materials. Significant improvements in the peak temperature coefficient of resistivity (TCR) and resistivity (ρ) were observed across all ceramic samples when the mol% of Sr was adjusted. The low ρ and large TCR values resulted from a combination of two factors. First, the presence of Sr led to the increase in the grain size and decrease in the number of boundaries, which improved the electrical transport and reduced the boundary scattering effects. This resulted in additional improvement in the grain arrangement order. Second, the cell volume (Vcell) and octahedron volume (Voct) both decreased first and then increased. The MnO6 octahedron underwent gradual deformation into a flattened shape, which facilitated carrier migration and increased electrical sensitivity of the material. The ceramic with x = 0.03 maintained high and stable TCR values in different working environments, both without a magnetic field (TCRo, 54.76% K−1) and in the presence of a vertical field (TCR⊥, 33.33% K−1). Furthermore, the material exhibited a low resistivity and a higher insulator–metal transition temperature (Tp). Performance differences among the samples were comprehensively and systematically explained by conducting cross magnetic field tests with field directions parallel and perpendicular to the flat surface of the bulk material, respectively. Overall, the findings of this study indicate that these ceramics act as promising candidates for future applications in information storage devices and magnetic sensors.

Oil-medium current annealing enhanced giant magneto-impedance properties of Co-based metallic microfibers for magnetic sensor applications

Herein, the effect of oil-medium current annealing on GMI characteristics of rotated-dipping Co-based metallic microfibers was investigated systematically. Based on thermophysical parameters of the metallic microfibers (containing glass transition temperature Tg and initial crystallization temperature Tx1), we constructed a steady-state heat conduction model by ANSYS to simulate the temperature field distribution during its oil-medium current annealing process, and further to determine the annealing current intensity range: 50 mA˜300 mA, according to the crystallization degree of cores of microfibers. The experimental results indicated that, in comparison to as-cast Co-based microfibers, the maximum GMI ratio [ΔZ/Zmax]max and the maximum magnetic field response sensitivity ξmax of oil-medium current annealed microfibers were both significantly improved. Among which, [ΔZ/Zmax]max and ξmax of the microfibers annealed at 225 mA can reach 303.1% and 50.6%/Oe, respectively, at the excitation current frequency f =5 MHz, and the maximum response field Hp increased from 1 Oe to 3 Oe. Meanwhile, the magnetic domain arrangement of oil-medium current annealed microfibers became denser, the width of which got smaller, and the transition regions of domain changed into clearer. This improvement of GMI characteristics is closely related to magnetic domain distribution regulated by high-intensity toroidal magnetic field, which was generated during the medium current annealing process. That is, the atomic magnetic moment tends to be closely and orderly adjusted by the combined action of both the magnetic field energy and thermal activation energy.

Current-perpendicular-to-plane giant magnetoresistance effects using Heusler alloys

A half-metal is an ideal spin source to realize extremely large magnetoresistance effects because of the completely spin-polarized density of states at the Fermi level, and Heusler alloy is a material class for which several compositions are known to exhibit half-metallic properties. Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effect is a resistance change that depends upon the relative angle of the magnetization vectors in magnetic layers separated by thin non-magnetic layer(s), which can be utilized for magnetic sensor applications. Over the last decade, the resistance change of CPP-GMR has been found to enhance greatly when using half-metallic Heusler alloys. In this article, the history of Heusler alloy based CPP-GMR is briefly reviewed, including the authors’ recent results on the analysis of the spin asymmetry coefficients based on the Valet-Fert model. Finally, the degradation of half-metallic spin polarization at interfaces is discussed and a future prospect is described.

Fabrication of FM/NM/FM Hetero-Structure Multilayers and Investigation on Structural and Magnetic Properties: Application in GMI Magnetic Sensors

Magnetic thin films of Fe/Cu/Fe and Fe/Cu/Ni multilayers on glass substrates were deposited by thermal evaporation route. The structure and morphology of multilayers were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). Amorphous formation of the Fe and Ni in multilayer structures and the maximum surface roughness of about 6.11 nm for the Fe/Cu/Fe and 4.8 nm for the Fe/Cu/Ni thin films were observed. Also, magnetization behaviors in perpendicular and parallel fields to the surface were investigated. The behavior of the magnetization indicates a low 5-mT coercive field, the easy in-plane magnetization, and the formation of soft ferromagnetic structure. The giant magneto-impedance response (GMI) to the applied longitudinal magnetic field at 5-MHz frequency was obtained 70% for three-layer Fe/Cu/Fe. Also, the measurements for the Fe/Cu/Ni film show a peak in the external field of about Hext = 14 Oe and the GMI response of about 95% at 5-MHz frequency. This work provides a preliminary investigation into the high performance of multilayer-based GMI devices for sensor applications.

Magnetoelectric Zn0.2Co0.8Fe2O4-PbZr0.58Ti0.42O3 nanocomposite for bistable memory and magnetic field sensor applications

Abstract The spinel ferrite based nanocomposite (Zn0.2Co0.8Fe2O4-PbZr0.58Ti0.42O3) has been prepared through a chemical process to observe the magnetoelectric and memory effect at room temperature. The structural and surface characterization of the nanoparticles reveal the presence of both the phases having crystallites size in nanometric regime, which are uniformly distributed. The observed nonlinear behaviour of the current of magnetic field dependent current-voltage characteristic may be due to the oxygen vacancy and defect states at the grain boundaries of the granular system. The sharp increased in nature of current is attributed to the space charge polarization and the space charge limited current determining through Child’s law. The maximum value of current is found to ~60 μA in presence of 15 V at ~2 kOe. Moreover, the change of open circuit current is found to ~71% in magnetic field. The DC electrical property of the nanocomposite shows two separate resistance states. Furthermore, the magnetic field dependent resistance is varying with an applied electric field and vice-versa. These features are a demonstration of good magnetoelectric coupling between the piezoelectric and piezomagnetic order parameters. The magnetoelectric coupling coefficient of the nanocomposite may be attributed to the magnetostriction properties of the piezomagnetic phase. The magnetoelectric coupling coefficient is largely depending on the direction of an applied magnetic field for the directional dependent magnetostriction properties of the piezomagnetic phase. The maximum value of the coupling coefficient has been found to ~4.5 mV/cm-Oe at room temperature. Furthermore, an applied AC magnetic field dependent magnetoelectric voltage coefficients of the nanocomposite have been estimated, which is completely matched with an observed value. This nanocomposite demonstrates the presence of memory effect, resistive switching behaviour, magnetoelectric coupling, etc.

Tunable band gap and enhanced ferromagnetism by surface adsorption in monolayer Cr2Ge2Te6

Two-dimensional (2D) van der Waals (vdW) materials have attracted significant attention for their promising applications in spintronic devices. Here, using first-principles calculations and renormalized spin-wave theory, we investigate the influence of surface adsorption (H and alkali metals) on the bandgap and ferromagnetism of monolayer ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$. We find that H-atom adsorption maintains the bandgap of ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$ around 0.95 eV but leads to a nearly indirect-to-direct band gap transition, while alkali-metal adsorption removes the bandgap and induces metallicity. More importantly, both H and alkali-metal adsorption surprisingly make the magnetic anisotropy energy four times larger than that of pristine ${\mathrm{Cr}}_{2}{\mathrm{Ge}}_{2}{\mathrm{Te}}_{6}$, leading to an increase of ${T}_{\mathrm{c}}$ by about 33%. Our findings of adsorption-controlled bandgap and magnetism in a 2D vdW magnet may open up opportunities for potential applications for new-generation magnetic memory storage, sensors, and spintronics.

The Phase Diagram and Exotic Magnetostrictive Behaviors in Spinel Oxide Co(Fe1-xAlx)2O4 System.

We report the magnetic and magnetostrictive behaviors of the pseudobinary ferrimagnetic spinel oxide system (1−x)CoFe2O4–xCoAl2O4 [Co(Fe1−xAlx)2O4], with one end-member being the ferrimagnetic CoFe2O4 and the other end-member being CoAl2O4 that is paramagnetic above 9.8 K. The temperature spectra of magnetization and magnetic susceptibility were employed to detect the magnetic transition temperatures and to determine the phase diagram of this system. Composition dependent and temperature dependent magnetostrictive behaviors reveal an exotic phase boundary that separates two ferrimagnetic states: At room temperature and under small magnetic fields (∼500 Oe), Fe-rich compositions exhibit negative magnetostriction while the Al-rich compositions exhibit positive magnetostriction though the values are small (<10 ppm). Moreover, the compositions around this phase boundary at room temperature (x = 0.35, 0.4, 0.45, 0.5) exhibit near-zero magnetostriction and enhanced magnetic susceptibility, which may be promising in the applications for magnetic cores, current sensors, or magnetic shielding materials.

Magnetic field induced martensitic transition in Fe doped Ni-Mn-Sn-B shape memory ribbons

In this study, effect of the Fe-doping on the microstructural evolution, phase transformation and magnetoresistance properties of the Ni-Mn-Sn-B magnetic shape memory ribbons fabricated by melt-spinning technique were investigated. While the phase transition temperatures from austenite to martensite in the undoped ribbon was very close to room temperature, it was found that they decreased by the Fe-doping, which was attributed to decrease in the e/a value with the Fe-content. A voltage change of 5 μV at a constant current of 1 mA and at 283 K and in the magnetic range of 0–10 kOe was obtained, which is good value obtained for the Heusler alloys. The resistivity data measured in the martensitic − austenite transition region was overlapped at ∼90 kOe, which is clear evidence for the magnetic field-induced one way martensitic transition. The ribbons showed an antiferromagnetic behavior at low magnetic field and a ferromagnetic behavior at high magnetic fields. The Fe-doping to the Ni-Mn-Sn system caused a significant increase in the magnitude of the magnetization. The results showed that the melt-spinning technique used in the production of magnetic shape memory strips is very promising for magnetic sensor applications.

MgO based specular spin valve with reversible minor loop and higher exchange bias for futuristic linear magnetic field sensor

Specular spin valves (SVs) containing ultrathin MgO, structured as substrate/seed/AF/PL1/MgO/PL2/Cu/FL/MgO/cap, have been fabricated. Both structural and magnetic characterizations of MgO based specular spin valve (SSV) have been performed and compared them with the measured data on naturally oxidized (NO) and conventional spin valves (CSV), grown under optimised condition. Reversible minor loop characteristics, highest exchange bias of 625 G and 10% magnetoresistive (MR) ratio were important observations in MgO based system. Zero hysteresis behavior was confirmed due to the reduction of grain growth of the stacks above the fine-textured MgO layer, through X-ray diffraction measurements. Interestingly, at 10 K, above 100% enhancement in MR ratio was observed in MgO based system with marginal increase in coercivity of the order 1 G. On the other hand, NO based structure has 10% MR, minor loop hysteresis of ∼2 G and exchange bias of ∼560 G at room temperature; however at 10 K, only 75% enhancement in MR ratio with large anomalies in magnetic measurements attributes due to the AFM nature of oxide materials. The above studies reflects the superior performance of MgO based SSV over a wide range of temperature in comparison to other SV structures and may lead to futuristic linear magnetic field sensor applications.

An Electrochemical Approach for Development of Novel Magnetic Multicomponent Alloy Thin Films for Sensor Applications

Magnetic multi-component alloys (MCAs) are the new class of multicomponent alloys where, combination of magnetic properties can be tuned with the composition. Due to their significant performance, MCAs have been proposed as the most appropriate choice of materials for several magnetic based sensor applications such as magnetoresistive sensors, etc. At times, for each application, multilayers with specific combination of magnetic properties or morphology throughout the material is required. In such cases, composition of alloying elements plays a significant role in the magnetic behaviour. Electrochemical approach in aqueous media is the most cost-effective method and favours better control over the composition with the help of pulse parameters. Therefore, major focus of the present work is to replace the non-aqueous/organic electrolytes with aqueous electrolytes for synthesizing the MCAs with five and/or six elements through electrodeposition. To the best of our knowledge, there haven’t been any reports on deposition of five principle alloying elements by an electrochemical approach in a single step using an aqueous media. The present study reveals the details on electrochemical deposition of multicomponent alloy thin films (Fe, Co, Ni, X, Y) for magnetic sensor applications. Firstly, a single step approach to develop nanocrystalline Fe-Co-Ni-X-Y (X, Y: Transition elements) MCA thin films is presented. Subsequently, the control over composition of MCA thin films and preliminary studies on their magnetic behaviour will be discussed. Finally, tuning of the magnetic properties of MCAs, such as saturation magnetization, magnetic permeability, and coercivity with respect to composition will be discussed. Based on the performance, these MCA thin films will be categorized for specific sensor applications. As it is important to understand the microstructure and composition of these MCA thin films, preliminary characterisation has been carried out using X-ray diffraction, scanning electron microscopy. For transmission electron microscopy (TEM), specimens have been prepared using focused ion beam (FIB) and analytical scanning/transmission electron microscopy including energy dispersive spectroscopy and electron energy loss spectroscopy have been carried out. The magnetization reversal curves for the MCA thin films were acquired initially using Kerr microscopy and detailed magnetic characterization will be carried out using physical property measurement system (PPMS) with a vibrating sample magnetometer. All the comprehensive details of this study will be discussed during the presentation.