GMR Effect Research Articles

Prospective Review of Magneto-Resistive Current Sensors with High Sensitivity and Wide Temperature Range

Current sensors play a vital role in power systems, industrial production, smart devices and other fields, which can provide critical current information in the systems for the safety and efficiency managements. The development of magneto-resistive effect technology in recent years expedites the research process of the current sensors in industrial-level applications. In the review, starting with the development status of the current sensors, the physical mechanisms of the relevant magneto-resistive effects and their early applications as the current sensors are introduced. Several design methods of the magnetic sensors, as well as their merits and shortcomings, are summarized. The performance parameters of the magnetic sensors based on AMR, GMR, TMR and Hall effects are reviewed, including the front-end amplification circuits and conditioning circuits. The industrial applications of the current sensors in the fields of automobiles and photovoltaic inverters are enumerated. The criterions for the current sensors to be used in different scenarios are discussed. In the future, it is imperative to continue the research and development of novel current sensors in order to satisfy the increasingly stringent demands of the industrial developments, in terms of the performance, cost and reliability of the current sensors.

Contribution of surface scattering to the GMR effect in the magnetic multilayer films

Contribution of surface scattering to the GMR effect in the magnetic multilayer films

Full Antiferroelectric Performance and GMR Effect in Multiferroic La0.75Ba0.25Fe12O19 Ceramic

The potential application of multiferroic materials in new electronic devices attracts more and more attention from people either in an academic field or industry. This paper reports that M-type lanthanum-doped barium ferrite (La0.75Ba0.25Fe12O19) demonstrates full antiferroelectric (AFE) and excellent magnetoelectric coupling effects at room temperature, while its AFE phase displays a zero macroscopic net polarization. The dramatic change in the dielectric constant near the Curie temperature far below room temperature represents the transition from ferroelectrics (FE) to antiferroelectrics. The fully separated double electric polarization hysteresis (P–E) loops confirmed its AFE performance. Its EF and EA are located at 1100 kV/cm and 850 kV/cm, respectively. The large M–H loop showed a strong magnetic property simultaneously. The UV-Vis-NIR optical spectrum revealed that La0.75Ba0.25Fe12O19 is also a semiconductor, whose direct bandgap energy (Eg) was determined to be 1.753 eV. Meanwhile, La0.75Ba0.25Fe12O19 showed strong ME coupling and a GMR effect. A 1.1 T magnetic field reduced its resistance by 110% at 30 kHz. The multiple functions combined in one phase would create new options for high energy storage capacitors, microactuators, pyroelectric safety sensors, cooling devices, and pulsed power generators and so on, as well as great opportunities for generating new electronic devices with active magnetoelectric coupling effects.

A novel method for fabricating guided-mode resonance filters by dip-coating colloidal nanospheres

A guided-mode resonance filter (GMRF) with nanosphere grating layer fabricated by a modified dip-coating method is designed and demonstrated through experiment. The influence of waveguide thickness, radius of nanosphere, incident angle and polarization characteristics on the spectral reflectance are investigated, and optimized structure parameters are obtained. Field distributions of the designed GMRF at resonance and non-resonance wavelength are simulated, and proved that GMR effect will generate when strong coupling occurs between the waveguide layer and the grating layer. In the end, GMRF with 260 nm diameter nanospheres grating layer is experimentally fabricated, neat hexagonal close row structure and a maximum reflectance of 82 % at around 402.3 nm wavelength are obtained.

TPV radical-based multifunctional molecular spintronic device: A first-principles study

We design a multifunctional molecular spintronic device consisting of two 1,3,5-triphenylverdazyl (TPV) radicals with carbon nanotube bridge and electrodes , and investigate its spin-polarized transport properties using the first-principles density functional theory and nonequilibrium Green's function method. The results show that the spin-polarized transport properties depend strongly on the external magnetic field modulation and high-efficiency spin-filtering, giant magnetoresistance , spin-rectifying and low-bias voltage negative differential resistance effects can be realized in this designed device. The mechanisms are proposed for these interesting physical effects based on the bias-dependent spin-resolved transmission function, projected density of states and corresponding molecular projected self-consistent Hamiltonian orbitals analysis. These results hold great potential for the development of high-performance multifunctional molecular spintronic devices. High-efficiency spin-filtering, giant magnetoresistance, spin-rectifying and low-bias voltage negative differential resistance effects are realized in a TPV radical-based molecular spintronic device with carbon nanotube bridge and electrode. • Spin-polarized transport properties of a TPV radical-based molecular spintronic device are investigated. • Spin-polarized transport properties depend strongly on the external magnetic field modulation. • High-efficiency spin-filtering, GMR, spin-rectifying and low-bias voltage NDR effects are realized.

Geometrical magnetoresistance effect and mobility in graphene field-effect transistors

Further development of graphene field-effect transistors (GFETs) for high-frequency electronics requires accurate evaluation and study of the mobility of charge carriers in a specific device. Here, we demonstrate that the mobility in the GFETs can be directly characterized and studied using the geometrical magnetoresistance (gMR) effect. The method is free from limitations of other approaches since it does not require an assumption of the constant mobility and the knowledge of the gate capacitance. Studies of a few sets of GFETs in the wide range of transverse magnetic fields indicate that the gMR effect dominates up to approximately 0.55 T. In higher fields, the physical magnetoresistance effect starts to contribute. The advantages of the gMR approach allowed us to interpret the measured dependencies of mobility on the gate voltage, i.e., carrier concentration, and identify the corresponding scattering mechanisms. In particular, the range of the fairly constant mobility is associated with the dominating Coulomb scattering. The decrease in mobility at higher carrier concentrations is associated with the contribution of the phonon scattering. Analysis shows that the gMR mobility is typically 2–3 times higher than that found via the commonly used drain resistance model. The latter underestimates the mobility since it does not take the interfacial capacitance into account.

Bi Layer Properties in the Bi–FeNi GMR-Type Structures Probed by Spectroscopic Ellipsometry

Bismuth (Bi) having a large atomic number is characterized by a strong spin–orbit coupling (SOC) and is a parent compound of many 3D topological insulators (TIs). The ultrathin Bi films are supposed to be 2D TIs possessing a nontrivial topology, which opens the possibility of developing new efficient technologies in the field of spintronics. Here we aimed at studying the dielectric function properties of ultrathin Bi/FeNi periodic structures using spectroscopic ellipsometry. The [Bi(d)–FeNi(1.8 nm)]N GMR-type structures were grown by rf sputtering deposition on Sitall-glass (TiO2) substrates. The ellipsometric angles Ψ(ω) and Δ(ω) were measured for the grown series (d = 0.6, 1.4, 2.0, and 2.5 nm, N = 16) of the multilayered film samples at room temperature for four angles of incidence of 60∘, 65∘, 70∘, and 75∘ in a wide photon energy range of 0.5–6.5 eV. The measured ellipsometric angles, Ψ(ω) and Δ(ω), were simulated in the framework of the corresponding multilayer model. The complex (pseudo)dielectric function spectra of the Bi layer were extracted. The GMR effects relevant for the studied Bi–FeNi MLF systems were estimated from the optical conductivity zero-limit (optical GMR effect). The obtained results demonstrated that the Bi layer possessed the surface metallic conductivity induced by the SOC effects, which was strongly enhanced on vanishing the semimetallic-like phase contribution on decreasing the layer thickness, indicating its nontrivial 2D topology properties.

Tuning ferroelectrics to antiferroelectrics in multiferroic LaxSr1−xFe12O19 ceramics

The combination of antiferroelectricity (AFE) and ferromagnetism (FM) in one structure would allow the development of new type of multiferroic candidates, which be applicable not only in magnetoelectric memories but also in novel energy storage devices. Here we propose a novel type of multiferroic candidate LaxSr1-xFe12O19, whose room temperature state could betuned from ferroelectrics (FE) to antiferroelectrics by changing x from 0 to 0.5. The emphasis of this paper will be focused on the La0.5Sr0.5Fe12O19 system, in which full AFE and FM coexist. The pure antiferroelectric behavior in La0.5Sr0.5Fe12O19 ceramics is demonstrated by double polarization-electric field (P-E) hysteresis loops, which are fully separated by a linear antiferroelectric AFE component with zero net polarization. The material of La0.2Sr0.7Fe12O19 with the intermediate composition exhibits a hybrid ferroelectric/antiferroelectric state. The recoverable energy density of the antiferroelectric La0.5Sr0.5Fe12O19 phase reaches 14.3 J/cm3. This material demonstrates strong magnetoelectric coupling and giant magnetoresistance (GMR) effect. A 1.1T magnetic field generates electronic polarization up to 0.95uC/cm2, reduce the resistance by 117%, enhances dielectric constants by 540% and right shifts the maximum dielectric loss peak by 208 kHz. The combined functional responses provide an opportunity to develop novel multifunctional electric and energy storage devices.

Investigating magneto-resistance in transition metals doped silicene nanoribbons

The Magneto Resistance (MR) is investigated in magnetic impurity-doped Zigzag Silicene Nano-Ribbons (ZSiNR) through Density Functional Theory (DFT) and Non-Equilibrium Green's Functions (NEGF) formalism using different spin configurations (Ferromagnetic (FM) and Antiferromagnetic (AFM)) in electrodes. The MR is calculated, and results show a GMR of about 2 ​× ​104% at 0.01V bias voltage for up-spin electrons in Co@ZSiNR structure and a total GMR of 2.6 ​× ​104% at 0.02V, which makes the proposed structures as possible candidates in spintronic device applications. The structures are modified by adding the impurities to the electrodes region, and removing the Hydrogen passivation. The GMR effect is investigated in these structures with different widths, which improves GMR ratios in certain widths.

Magnetoresistive Effects in Co/Pt-Based Perpendicular Synthetic Antiferromagnets

In this study, Co/Pt based perpendicular synthetic antiferromagnetic (p-SAF) structures with Ru interlayers are investigated with regard to their magnetotransport properties. The p-SAF structures are varied in their number of Co/Pt multilayer (ML) stacks and Ru interlayers, and are examined for changes in their magnetoresistive effects. The alignment of magnetization directions of the MLs in the ML/Ru/ML stacks of the p-SAF generates a giant magnetoresistance effect (GMR), while the anisotropic magnetoresistance effect (AMR) at each ML further influences the resistance of the system. The GMR is found to increase linearly with the number of Ru interlayers. To extract contributions from the AMR, a simple model is proposed, which explains the observed transfer curves where both effects are taken into account. For the AMR amplitude, it is observed that longitudinal AMR contributions decrease with increasing numbers of Co layers in the p-SAF, whereas transverse components remain constant. While the highest GMR effects are measured at low temperatures, only longitudinal AMR contributions appear to be significantly affected by the measurement temperature.

The influence of the atomic scale interface roughness on the GMR effect in Fe/Cr multilayers

In this study, we analysed Fe/Cr multilayers that had been modified by Bi, In, and Pb surfactants. Their structure, morphology and interface roughness were investigated using low-energy electron diffraction, Auger electron spectroscopy (AES), X-ray reflectivity and conversion electron Mössbauer spectroscopy (CEMS). The magnetic and magnetotransport properties of the multilayers were studied by measuring the Kerr effect and four-point magnetoresistance, respectively.We observed that the Bi surfactant caused a slight interface smoothening while the introduction of In and Pb surfactants had a negative influence on the epitaxial growth of Fe and Cr, which were associated with an increase of interface roughness. These changes did not destroy the layer continuity, which was confirmed by AES measurements. The magnetic measurements revealed an antiferromagnetic coupling of the Fe layers for the as-deposited sample as well as for the Bi and Pb-modified multilayers and its partial reduction for the In-modified sample. We observed that the increase of interface roughness that had originated from atom intermixing resulted in a reduction of the giant magnetoresistance. In these investigations in which CEMS studies were used, we were able to distinguish between the interface roughness that was caused by atom intermixing and interface corrugation.

Caused by the giant magnetoresistive effect changes of microwave refractive index

Studies of the interaction of electromagnetic microwaves with [Co88Fe12/Cu]n, nanostructures, in which the giant magnetoresistive effect (GMR) shows itself, have been carried out. It is established that the GMR effect contributes to changes in the microwave complex refraction coefficient, including the refractive index.

High GMR Effect and Perfect Microstructure in CoFe/Cu Multilayers

CoFe-/Cu-based multilayers with two different types of a buffer layer, NiFeCr, and Ta/NiFeCr have been produced by magnetron sputtering. The crystal structure of the superlattice layers has been studied. A correlation between the features of the microstructure and the magnitude of the magnetoresistance has been found. Superlattices with giant magnetoresistive effect reaching up to 83% have been fabricated.

Observation of Anomalous Spin Torque Generated by a Ferromagnet

In this work we report observation of in-plane current induced out-of-plane magnetic field driven torque in spin valve structure. Since ferromagnet has high spin orbit coupling it is expected to be the source of spin-orbit-torque as it possesses anomalous-Hall-effect (AHE: equivalent to spin Hall effect in heavy metal). So we have carried out spin-torque ferromagnetic resonance (ST-FMR) experiment in a spin valve (consists of a fixed magnet and a free magnet which are separated by Cu spacer), passing in-plane radio frequency current and measuring DC voltage. Our experimental results eventually indicate that spin torque exerted on the free magnet is not caused due to the spin current injection by the fixed magnet owing to its AHE, but it is originated from in-plane current driven out-of plane effective magnetic field. This is new class of spin torque which is completely different from Slonczewski-spin transfer torque and Rashba like field like torque. The effective out-of plane magnetic field depends on the direction of current (in-plane) and magnetization (in-plane) of the pinned layer. One possible mechanism behind this unconventional torque could be intefacial spin-scattering which is also origin of current in-plane GMR effect. Most importantly this effective out-of plane torque can be useful to switch out-of plane magnetic bits in spintronic memory application.

Electron transport in all-Heusler Co2CrSi/Cu2CrAl/Co2CrSi device, based on ab-initio NEGF calculations

Based on the ab-initio non-equilibrium Green’s function (NEGF) formalism based on the density functional theory (DFT), we have studied the electron transport in the all-Heusler device Co2CrSi/Cu2CrAl/Co2CrSi. Results show that the calculated transmission spectra is very sensitive to the structural parameters and the interface. Also, we obtain a range for the thickness of the spacer layer for which the MR effect is optimum. Calculations also show a perfect GMR effect in this device.

GMR effect and Kondo-like behaviour in Co-Cu microwires

The influence of annealing on structure and temperature and magnetic field dependences of resistance of Cu100-xCox (x = 5, 10, 20) glass-coated microwires prepared using Taylor-Ulitovsky has been studied.All Cu100-xCox microwires present resistivity minimum at certain temperature, Tm. This minimum is very well defined for as-cast samples. Tm-values decrease after annealing (from about 50 K to about 25 K). Observed R(T) dependences and the minimum are well affected by applied magnetic field.Additionally we observed a significant increasing of the GMR effect in the annealed samples (at 400 °C) with long enough annealing time (up to 34% GMR effect).Considerable enhancement of the GMR effect related with structural changes of the studied samples is promising for technical applications.

Предметные олимпиады как показатель качества обучения

The famous phrase of M.V. Lomonosov: "Mathematics
 should be studied for it puts mind in order". It is quite possible to
 rephrase it for descriptive geometry, because geometry is math too.
 The invention of microprocessor technology, the advent of the
 personal computer, the discovery of the GMR effect (1988), which
 dramatically increased the speed and memory capacity of the PC,
 are called theSubject olympiads in descriptive geometry are held
 in many cities of Russia, including in Moscow. These olympiads,
 according to the author of the hundred-Tue, are an indicator of
 the quality of teaching in universities. Introduced by the author at
 the Moscow State Institute of Public Utilities (MIKHiS), and then
 at the Moscow State Academic Art Institute named after V.I. Surikov
 course of descriptive geometry, which allows to organize and algorithmization
 of the educational process, helped students teams of
 both universities without any special additional of preparation to
 take a pretty decent place at the Moscow city Olympiads on descriptive
 geometry. The structure of the basic course helped to
 organize and sturcture lecture material, which, in turn, allowed the
 entire amount of information to compress, in principle, by almost
 half, and reduce the number of hours of lectures from 32 to 18
 without much loss. If current trends to cut a watch from the disciplines
 of engineering, it is the doubtless achievement. The use of
 this structure led to a positive effect: better memorization of the
 material, better absorption, which was identified with the participation
 of students who passed the course at the Moscow city Olympiads
 on descriptive geometry. The author developed the criterion of
 success of the team of students. The article contains the appropriate
 tables and charts.
 The article does not provide data later than 2013, as Moscow
 State Academy of Municipal Economy and Construction was
 disbanded in 2014 and included in Moscow State University of
 Civil Engineering. From the very beginning, the comparison of the
 two approaches in Moscow State Academy of Municipal Economy
 and Construction and in Moscow State Academic Art Institute
 named after V.I. Surikov was considered: traditional teaching descriptive
 geometry and proposed.

Ломоносов и компьютерные технологии в обучении начертательной геометрии

The famous phrase of M.V. Lomonosov: "Mathematics
 should be studied for it puts mind in order". It is quite possible to
 rephrase it for descriptive geometry, because geometry is math too.
 The invention of microprocessor technology, the advent of the
 personal computer, the discovery of the GMR effect (1988), which
 dramatically increased the speed and memory capacity of the PC,
 are called the fourth information revolution in the history of mankind.
 The whole world took note of this and began to apply, only
 in Russia some extreme reformers of geometry assumed that if
 computer graphics arose, it might well replace geometry.
 Computer graphics, of course, can be applied to solve various
 geometric problems. But what is important for a University that
 aims to teach? The process of learning or the mere result on display
 obtained just by pressing the buttons? More important is how this
 result is obtained and with what algorithm. Therefore, the feasibility
 of the use of graphic programs in solving typical tasks of descriptive
 geometry is very much an open question.
 A student solving the task via computer is concerned not with
 the search of geometric algorithm, but with the search of a suitable
 option that could give an answer. But not all geometrical problems
 are amenable to the available buttons.
 Submerged into virtual world, a student begins to think in terms
 of this world and cease to be aware and to pay attention to fundamental,
 basic geometric regularities taught in descriptive geometry
 course.
 Comparing geometric and computational algorithms is incorrect
 because there is no knowledge of the “hidden files” of graphic
 editor. We can assume that the iterative scheme is implemented.
 Frontal iterative computer graphics schemes are good for getting
 answers, but unsuitable for the study of constructive geometry
 methods.

Magnetoresistance behavior of Ni80Fe20/Ru/Ni80Fe20 nanostripes

We present a systematic investigation on the effects of interlayer coupling on the magnetoresistance (MR) behavior of Ni80Fe20/Ru(\( t_{Ru}\)/Ni80Fe20 trilayer nanostripes (NSs) as a function of temperature T . By changing \( t_{Ru}\) from 0.8 nm to 1.7 nm, either a ferromagnetic or an antiferromagnetic (AFM) type of interlayer coupling was achieved, leading to a markedly different MR behavior. We observed that the MR response is a superimposition of AMR and GMR effects, and it is significantly dependent on temperature. For AFM coupled NSs, there is a transition from a pure AFM state to a reversed spin-flop phase due to enhanced ferromagnetic pin-hole coupling at low T. Our experimental results are in good agreement with micromagnetic simulations.

Perfect GMR effect in gapped graphene-based ferromagnetic–normal–ferromagnetic junctions

We investigate the quantum transport property in gapped graphene-based ferromagnetic/normal/ferromagnetic (FG/NG/FG) junctions by using the Dirac–Bogoliubov–de Gennes equation. The graphene is fabricated on SiC and BN substrates separately, so carriers in FG/NG/FG structures are considered as massive relativistic particles. Transmission probability, charge, and spin conductances are studied as a function of exchange energy of ferromagnets (h), size of graphene gap, and thickness of normal graphene region (L) respectively. Using the experimental values of Fermi energy in the normal graphene part (EFN ∼ 400 meV) and energy gap in graphene (260 meV for SiC and 50 meV for BN substrate), it is shown that this structure can be used for both spin-up and spin-down polarized current. The latter case has different behavior of gapped FG/NG/FG from that of gapless FG/NG/FG structures. Also perfect charge giant magnetoresistance is observed in a range of .