Magnetic Electrode Research Articles

Electrochemical sensor for sensitive nitrite and sulfite detection in milk based on acid-treated Fe3O4@SiO2 nanoparticles

In this work, a simple electrochemical sensing platform based on acid-treated Fe3O4@SiO2 nanoparticles was successfully prepared for nitrite and sulfite detection. Fe3O4@SiO2 nanoparticles were synthesized through the sol–gel and hydrothermal methods. Fe3O4@SiO2 presented positive charges after acid treatment, which could enhance the electrostatic attraction between Fe3O4@SiO2 and nitrite and sulfite. The Fe3O4@SiO2(acid-treated) modified magnetic glassy carbon electrode (MGCE) was applied to detect nitrite and sulfite using differential pulse voltammetry and cyclic voltammetry. Under optimized conditions, the developed electrochemical sensor presented good analytical properties for nitrite and sulfite detection with detection limits of 3.33 μmol/L and 31.57 μmol/L, respectively. The good recoveries varied from 85.18% to 111.02%, with a relative standard deviation of 0.23–4.80%. Furthermore, the Fe3O4@SiO2(acid-treated) modified MGCE showed better selectivity, reproducibility, and repeatability in nitrite and sulfite detection. Therefore, this proposed electrochemical sensor provides a new method for developing a nitrite and sulfite detection sensor.

Effect of protonic acid concentration on electrical properties of fly ash magnetic beads/polyaniline composites

AbstractMagnetic polyaniline nanofibers were synthesized by oxidative polymerization using protonic acid and fly ash magnetic beads as dopants and ammonium persulfate as oxidant. The synthesized magnetic polyaniline was characterized by FT‐IR, UV, XRD and SEM, and its morphology and structure were revealed. Polyaniline magnetic electrodes were prepared by pressing method, and their electrochemical properties were analyzed by cyclic voltammetry and constant current charge–discharge methods. The capacities of polyaniline powders doped with optimal concentration of hydrochloric acid and p‐toluene sulfonic acid at current density of 1 A/g were 250.75 and 410.5 F/g, respectively. The magnetic polyaniline doped with optimal acid concentration has good conductivity through impedance measurement analysis. A smooth and uniform film was prepared by pressing magnetic polyaniline powder and its photosensitivity was observed under different monochromatic illumination. The results show that the current and voltage have a linear relationship and that different monochromatic light energies can be distinguished significantly with the increase of voltage.

Examining the Effects of Homochirality for Electron Transfer in Protein Assemblies.

Protein voltammetry studies of cytochrome c, immobilized on chiral tripeptide monolayer films, reveal the importance of the electron spin and the film's homochirality on electron transfer kinetics. Magnetic film electrodes are used to examine how an asymmetry in the standard heterogeneous electron transfer rate constant arises from changes in the electron spin direction and the enantiomer composition of the tripeptide monolayer; rate constant asymmetries as large as 60% are observed. These findings are rationalized in terms of the chiral induced spin selectivity effect and spin-dependent changes in electronic coupling. Lastly, marked differences in the average rate constant are shown between homochiral ensembles, in which the peptide and protein possess the same enantiomeric form, compared to heterochiral ensembles, where the handedness of the peptide layer is opposite to that of the protein or itself comprises heterochiral building blocks. These data demonstrate a compelling rationale for why nature is homochiral; namely, spin alignment in homochiral systems enables more efficient energy transduction.

Spin-dependent electrified protein interfaces for probing the CISS effect.

Bio-spinterfaces present numerous opportunities to study spintronics across the biomolecules attached to (ferro)magnetic electrodes. While it offers various exciting phenomena to investigate, it is simultaneously challenging to make stable bio-spinterfaces as biomolecules are sensitive to many factors that it encounters during thin-film growth to device fabrication. The chirality-induced spin-selectivity effect is an exciting discovery, demonstrating an understanding that a specific electron's spin (either up or down) passes through a chiral molecule. The present work utilizes Ustilago maydis Rvb2 protein, an ATP-dependent DNA helicase (also known as Reptin), to fabricate bio-spintronic devices to investigate spin-selective electron transport through the protein. Ferromagnetic materials are well-known for exhibiting spin-polarization, which many chiral and biomolecules can mimic. We report herein spin-selective electron transmission through Rvb2 that exhibits 30% spin polarization at a low bias (+0.5V) in a device configuration, Ni/Rvb2 protein/indium tin oxide measured under two different magnetic configurations. Our findings demonstrate that biomolecules can be put in circuit components without any expensive vacuum deposition for the top contact. The present study holds a remarkable potential to advance spin-selective electron transport in other biomolecules, such as proteins and peptides, for biomedical applications.

Label-free electrochemical biosensor with magnetically induced self-assembly for the detection of cancer antigen 125

Magnetically induced self-assembly technology was used to construct a label-free electrochemical biosensor based on magnetic Mg0.5Cu0.5Fe2O4-Au nanocomposites for the sensitive detection of cancer antigen 125 (CA125). To aim for this, Mg0.5Cu0.5Fe2O4 nanoparticles were first prepared via the rapid combustion process. The average diameter of the nanoparticles calcined at 800 °C with the absolute ethanol volume of 20 mL was about 169.3 nm. Then Au was used for the surface modification by NaBH4 reduction reaction approach. The magnetic glassy carbon electrode (MGCE) was modified by Mg0.5Cu0.5Fe2O4-Au via a magnetic induction self-assembly process. The reduced thiol-modified single-stranded DNA was attached to the Mg0.5Cu0.5Fe2O4-Au nanocomposites by Au-S bonds without any coupling agent. CA125 antigen was grabbed directly by its aptamer DNA due to its specific identification with the aptamer. Finally, the modified electrodes were blocked with BSA and then characterized. Finally, DPV analysis was used for CA125 detection, the novel fabricated biosensor demonstrated good detection properties for CA125 with a linear range of 5–125 U/mL and a detection limit of 4.4 U/mL. The results showed that the aptamer sensor had good specificity, repeatability, and stability. The feasibility of our sensor for the determination of CA125 was also demonstrated by measuring CA125 levels in serum using the Roche gold-standard instrument of the People’s Hospital of Danyang as the reference value. The recoveries of real serum samples were 94.65–101.71%, and RSDs were 1.26–4.65%. Moreover, the surface of the electrode could be cleaned and reused by magnetic separation, greatly reducing the cost and providing the possibility for a point-of-care test (POCT). This work demonstrated a new strategy for integrating both nanostructures and biocompatibility to build advanced cancer biomarker sensors with wide applications.

CoFe2O4 decorated graphene/C18-functionalized mesoporous silica nanocomposites prepared for magnetic enrichment and electrochemical detection of promethazine in beef

Promethazine (PHZ) is used as a sedative in veterinary medicine, and its residue can threaten the health of human. The electrochemical detection of PHZ is suitable method for application in the field. However, the traditional electroanalysis is difficult to perform directly in meat samples due to matrix interference. This work integrates magnetic solid-phase extraction and differential pulse voltammetry for highly sensitive and selective determination of PHZ in beef and beef liver for the first time. CoFe2O4/graphene coated with C18-functionalized mesoporous silica (MG@mSiO2-C18) is synthesized as dispersed magnetic adsorbent to extract PHZ. Magnetic glassy carbon electrode modified with nitrogen-doped hollow carbon microspheres (HCM) attracts the MG@mSiO2-C18 with PHZ, and directly detects the PHZ without elution procedure. MG@mSiO2-C18 can separate PHZ to avoid the interference of impurities on following detection, and also concentrate PHZ on magnetic electrode. Additionally, the electrode modification with HCM can amplify the electrochemical signal of PHZ. Finally, the integrated PHZ determination method exhibits a wide linear range from 0.08 µmol/L to 300 µmol/L with a low limit of detection of 9.8 nmol/L. The beef sample analysis presents excellent recovery, demonstrating that this protocol is promising for the rapid and onsite detection of PHZ in real meat samples

Magnetic Field-Enhanced Performance of Superparamagnetic LiMn2 O4 -Based Composite Slurry Electrode for Semisolid Flow Battery.

Semisolid flow batteries are expected to be applied to large-scale energy storage fields due to the combination of the high energy density of rechargeable batteries and the flexible design of flow batteries. However, electronic conductivity, specific capacity, and viscosity of slurry electrodes are generally mutually restrictive. Here, a new concept of semisolid flow batteries based on magnetic modification slurry electrode is proposed and the electrochemical performance of the semisolid electrode is expected to be improved by close contact and enhanced electronic conductivity between the active particles with the aid of external magnetic field. This concept is further demonstrated using superparamagnetic LiMn2 O4 -Fe3 O4 -carbon nanotube composite as semisolid cathode. It achieves a capacity of 113.7 mAh g-1 at a current density of 0.5mA cm-2 with the aid of external magnetic field (about 0.4 T), which is about 21% higher than that without external magnetic field. Simulation study also reveals this improvement mainly resulted from the increase of the conductive paths of electrons after the rearrangement of the active particles under the external magnetic field. It is believed that this strategy gives a new and effective method for controlling the viscosity and electronic conductivity of the slurry electrodes and related flowable electrochemical energy storage systems.

Highly sensitive spin-torque diodes based on in-plane magnetized magnetic tunnel junctions

We investigate the highly sensitive spin torque diode (STD) effect in a magnetic tunnel junction (MTJ) with an in-plane polarizer and an in-plane free layer. Under injection locking mechanisms, a high rectification voltage of 12 mV is obtained with an input radio frequency power of 1 μW under direct current bias current and a weak magnetic field, corresponding to a high sensitivity of 12 000 mV/mW. In addition, we use the nonlinear rectification characteristics of STD to mimic a neuron with a ReLU-like activation function to perform the recognition of handwritten digits in the Mixed National Institute of Standards and Technology database, where a produced accuracy of up to 93.53% is obtained. These findings suggest that the MTJ with in-plane magnetized electrodes holds promising potential in developing high sensitivity STDs for Internet of Things applications and neuromorphic computing.

GlycoEVLR: Glycosylated extracellular vesicle-like receptors for targeting and sensing viral antigen

Biosensors are rapid and portable detection devices with great potential for the instant screening of infectious diseases. Receptors are the critical element of biosensors. They determine the specificity, sensitivity and stability. However, current receptors are mainly limited to antibodies and aptamers. Herein, we developed a glycosylated extracellular vesicle-like receptor (GlycoEVLR) for the rapid detection of virus antigens, specifically using SARS-CoV-2 as a model. The human angiotensin-converting enzyme 2 (ACE2)-overexpressed and heparin-functionalized HEK-293T cell membrane-cloaked Fe3O4 nanoparticles (NPs) were prepared as functionalizing GlycoEVLR. They were characterized as spherical core–shell structures with a diameter of around 100 nm, which were perfectly comparable to natural extracellular vesicles. Binding affinities between GlycoEVLR and spike1 (S1) antigen were demonstrated using surface plasmon resonance (SPR). The GlycoEVLR was fixed on magnetic electrodes to construct electrochemical biosensors. Using electrochemical impedance spectroscopy (EIS) as a measurement technique, the S1 antigen was detected down to 1 pg/mL within 20 min and showed a good linearity range from 1 pg/mL to 1 ng/mL. Also, the GlycoEVLR-based electrochemical biosensors showed excellent antifouling performance and stability. Overall, our work provides a useful methodology for developing extracellular vesicle-like receptors for biosensors. Combining the inherit natural receptor proteins and antifouling lipids from the host cells with engineered glycan motifs to target and sense viral antigens will open a newavenue for biosensors.

KTX-이음 철도차량용 진공인터럽터 축자계 전극의 설계 및 검증

The main circuit breaker(MCB) used in railway vehicles has mainly applied a vacuum interrupter(VI) due to its long life and easy maintenance requirements. When an accident such as a short circuit or ground fault occurs in a railway vehicle, the VI may interrupt the fault current. The electrodes of the VI are closely related to the breaking performance, so it is very important to design the shape of them. In particular, when a high breaking capacity is required, such as railway vehicles, most manufacturers control the arc by applying a axial magnetic field electrode in VIs. For a axial magnetic field electrode, by diffusing the arc throughout the electrode surface by a magnetic field, melting of the contact can be minimized and the electrical endurance life can be improved. The breaking performance of VIs could be verified through a high power short-circuit test, but it takes a lot of cost and time, so most manufacturers evaluate the breaking performance through magnetic field analysis, but the validity of analysis result is not verified. In this study, an electrode of a vacuum interrupter applied to a high-speed vehicle was designed, and a magnetic field analysis was performed to verify its effectiveness, and a sample was manufactured for an actual electrode part to measure magnetic flux density. As a result of comparing the analysis and the measured values, similar results were confirmed in most parts except for the center and edge of the electrode, and the validity of the design was verified.

Large tunnel magnetoresistance in magnetic tunnel junctions with magnetic electrodes of metastable body-centered cubic CoMnFe alloys

A magnetic tunnel junction (MTJ) is a key device in spintronics applications, such as magnetoresistive random access memory (MRAM). Current standard magnetic material for MTJs is a body-centered cubic (bcc) FeCo(B), which shows large tunnel magnetoresistance (TMR) and high perpendicular magnetic anisotropy (PMA), both are crucial for high-memory capacities MRAM. It is demanded that magnetic materials showing TMR as well as PMA higher than FeCo(B) for further advance. One of alternative magnetic materials may be bcc Co since past ab-initio studies predict that bcc Co show large TMR effect in MgO-barrier MTJs and large PMA due to magneto-elastic effect for those strained state. However, bcc Co is thermodynamically unstable; thus, it is aimed to explore metastable bcc Co based alloys with high stability. Here, we propose metastable bcc Co based alloy with adding both Mn and Fe as a candidate. We study in-plane magnetized MTJs utilizing metastable bcc CoMnFe films as electrodes and demonstrate large TMR effect of 350% at 300 K and of 1002% at 5 K. This experimental finding will open a route to advanced bcc Co based magnetic material for MRAM applications.

MOF-derived magnetic trimetallic oxide-carbon nanocomposites for modification-free and dual molecular events-dependent ratiometric electrochemical analysis of intracellular glutathione

The response of ratiometric electrochemical signals toward the targets of interest generally depends on specific molecules-mediated single molecular recognition event, which limits the application in analyzing the targets without specific recognition molecules. In this work, novel dual molecular recognition events were proposed for rapid and reliable electrochemical analysis of glutathione (GSH) using MOF-derived trimetallic oxide-carbon (Fe3O4/CuO/NiO-C) nanocomposites. The binding of GSH to CuO caused a decrease in the oxidation signal of Cu(Ⅱ) due to the formation of nonelectroactive complex, while NiO could electrocatalyze the oxidation of GSH. These GSH-involved dual molecular recognition events guaranteed the readout of ratiometric electrochemical signals with a complementary response range, allowing sensitive and wide-range analysis of GSH. Besides, the difference in spatial conformation gave rise to a different oxidation potential for different biothiols, which guaranteed selective analysis of GSH. The presence of Fe3O4 allowed modification-free detection within 5 min using a magnetic working electrode. Taking advantage of these merits, the developed electrochemical sensor could rapidly and reliably monitor the intracellular GSH.

A strategy for As(III) determination based on ultrafine gold nanoparticles decorated on magnetic graphene oxide

In this work, a new dendrimer modified magnetic graphene oxide (GO) was used as a substrate for electrodeposition of Au nanoparticles. The modified magnetic electrode was employed for sensitive measuring of As(III) ion as a well-established human carcinogen. The prepared electrochemical device exhibits excellent activity towards As(III) detection using the square wave anodic stripping voltammetry (SWASV) protocol. At optimum conditions (deposition potential at −0.5 V for 100 s in 0.1 M acetate buffer with pH 5.0), a linear range from 1.0 to 125.0 μgL−1 with a low detection limit (calculated by S/N = 3) of 0.47 μg L−1 was obtained. In addition to the simplicity and sensitivity of the proposed sensor, its high selectivity against some major interfering agents, such as Cu(II) and Hg(II) makes it an appreciable sensing tool for the screening of As(III). In addition, the sensor revealed satisfactory results for detection of As(III) in different water samples, and the accuracy of obtained data were confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) setup. Accounting for the high sensitivity, remarkable selectivity and good reproducibility, the established electrochemical strategy has great potential for analysis of As(III) in environmental matrices.

Simultaneous separation of different magnetic particles by sputtering magnetic wires at the bottom of a microchip: Novel geometry in magnetophoresis

In this paper, sputtered magnetic electrodes at the bottom of the microchannel is used to separate different magnetic particles in a microfluidic device, simultaneously. The proposed design consists of a microchannel with a length of 30 mm with three different outlets. The Nickel electrodes with different angles and thicknesses are used to separate different particles. A permanent magnet is used to produce a uniform magnetic field and the presence of the magnetic wires disturbs the uniformity of the magnetic field which leads to magnetic force applied to the magnetic particles in the channel’s environment. In order to validate the results, numerical solution was compared with analytical relations. Important parameters such as microparticle size and characteristic (M−450, Myone, Oligo (dT)25), wire dimensions, wire spacing, wire angle and the flow rate were analyzed. The results show that M−450 particles are affected by greater force in comparison to Myone and Oligo (dT)25 microparticles due to their higher magnetism property and size. It was shown that by increasing the angle of the sputtered wires (at the bottom of the channel), the particle deviation was reduced. Also, the effect of wire thickness of the electrodes is investigated for thicknesses of 10, 15 and 20 μm. The maximum deviation was related to the thickness of 20 μm, thus, the particles were not able to pass off over the electrodes and moves along the wire path. By increasing the distance between the wires from 400 μm to 700 μm, the microparticle deviation was increased. As the flow rate of the inlet fluid increases (from 25 to 75 mm/s), the hydrodynamic force on the microparticles increases and therefore, the particle deviation decreases when crossing off over the electrodes. It is observed that for speed of 50 mm/s, the best separation efficiency (94%) was obtained for the proposed microchip design.

Specific Adsorption of Magnetic Fe3O4@hydroxyapatite Nanocomposites to a Hybridized Duplex for Immobilization and Label-Free Electrochemical Biosensing of MicroRNA

The unique discriminating ability of hydroxyapatite (HAP) to single- and double-stranded nucleic acid implies its potential as a biosensing material for nucleic acid analysis. Herein, a novel immobilization- and label-free electrochemical strategy has been developed for miRNA let-7a detection based on the specific adsorption of magnetic Fe3O4@hydroxyapatite (Fe3O4@HAP) to a duplex structure. Typically, the highly efficient homogeneous reaction between probe DNA (pDNA) and target miRNA let-7a produces the nucleic acid duplex, which is specifically adsorbed on the surface of Fe3O4@HAP. Thereafter, the electroactive intercalator Nile blue (NB) is introduced as the label-free signal molecule and inserts between the stacked base pairs of the pDNA–miRNA duplex. Thus, the Fe3O4@HAP bearing pDNA–miRNA and numerous intercalated NBs are adsorbed by the magnetic glassy carbon electrode, giving rise to an intense sensing signal without the need of nuclease-assisted cyclic amplification. With this advantage, the sensing system shows a wide linear range from 1.0 fM to 100 nM and a low detection limit of 0.051 fM for miRNA let-7a analysis. What is more, the synergy of the base-pairing-driven hybridization, the specific intercalation of NB to the duplex structure, and the selective adsorption of Fe3O4@HAP contribute to a high sensing specificity of the biosensing strategy. The sensing method provides a state-of-the-art strategy for the sensitive and facile bioanalysis and clinical diagnosis of miRNA.

Fascinating Immobilization-Free Electrochemical Immunosensing Strategy Based on the Cooperation of Buoyancy and Magnetism.

Rapid and accurate detection of biomolecules is of vital importance for the diagnosis of disease and for performing timely treatments. The point-of-care analysis of cancer biomarkers in the blood with low cost and easy processing is still challenging. Herein, an advanced and robust strategy, which integrates the buoyant recognition probe with the magnetic reporter probe in one solution, was first proposed for immobilization-free electrochemical immunosensing. The tumor marker of alpha fetoprotein (AFP) can be captured immune-buoyantly, and then a multifunctional magnetic reporter probe in pseudo-homogeneous solution was further captured to fulfill a sandwich-type immunoreaction. The residual magnetic reporter probe can be firmly and efficiently attracted on a magnetic glassy carbon electrode to fulfill the conversion of the target AFP amount into the residual magnetic electrochemical signal indicator. As a result, the electrochemical signal of methylene blue can accurately reflect the original level of target antigen AFP concentration. By integrating buoyancy-driven quasi-homogenous biorecognition with magnetism-mediated amplification and signal output, the proposed immobilization-free electrochemical immunosensing strategy displayed a wide range of linear response (100 fg mL-1 to 10 ng mL-1), low detection limit (14.52 fg mL-1), and good reproducibility, selectivity, and stability. The designed strategy manifests remarkable advantages including assay simplicity, rapidness, and high sensitivity owing to the in-solution instead of on-electrode biorecognition that could accelerate and improve the biorecognition efficiency. To the best of our knowledge, this is the first cooperation of buoyancy-driven biorecognition with magnetism-mediated signal output in bioanalysis, which would be attractive for rapid clinic biomedical application. Thus, this work provides a fresh perspective for convenient and favorable immobilization-free electrochemical biosensing of universal biomolecules.

Novel electrochemical sensing platform basing on di-functional stimuli-responsive imprinted polymers for simultaneous extraction and determination of metronidazole

A novel magnetic-controlled electrochemical sensor has been fabricated by combined photo-responsive surface molecular imprinted polymers (P-SMIPs) and electrochemical sensor. In particular, the P-SMIPs were obtained by living radical polymerization of photo-responsive functional monomer onto the magnetic Fe3O4 modified multi-walled carbon nanotubes nanocomposites. The magnetic glassy carbon electrode was introduced to make the anchoring and removal of P-SMIPs onto the magnetic-controlled glassy carbon electrode easy to manipulate. Driven by UV/vis light, the platform performs releasing and absorption of metronidazole basing on conformational variations of the photo-responsive monomer at the receptor sites part in the P-SMIPs. This process can be tested by the photo-responsive variations of metronidazole electrochemical signal. As the consequence, extracting of P-SMIPs sensor can be conveniently triggered by the controllable UV light intervention measure, leading to effectively improve in both analytes mass transfer rate to the receiving media and extraction efficiency. The experimental result indicated that the excellent recoveries of metronidazole were varied between 77.9% and 89.9% with RSDs ≤4.87% in the biological samples. Therefore, the P-SMIPs sensor shows satisfactory potential in reusable extractions that can be recycled several times with no significant loss of activity, and this utilization strategy can be extended to other analytes, achieving manifold applications of pharmaceutical and environmental.

Revealing the key role of molecular packing on interface spin polarization at two-dimensional limit in spintronic devices.

Understanding spinterfaces between magnetic metals and organic semiconductors is essential to unlock the great potentials that organic materials host for spintronic applications. Although plenty of efforts have been devoted to studying organic spintronic devices, exploring the role of metal/molecule spinterfaces at two-dimensional limit remains challenging because of excessive disorders and traps at the interfaces. Here, we demonstrate atomically smooth metal/molecule interfaces through nondestructively transferring magnetic electrodes on epitaxial grown single-crystalline layered organic films. Using such high-quality interfaces, we investigate spin injection of spin-valve devices based on organic films of different layers, in which molecules are packed in different manners. We find that the measured magnetoresistance and the estimated spin polarization increase markedly for bilayer devices compared with their monolayer counterparts. These observations reveal the key role of molecular packing on spin polarization, which is supported by density functional theory calculations. Our findings provide promising routes toward designing spinterfaces for organic spintronic devices.

Spin-charge-coupled transverse resistance in an ambipolar conductor YH2-based Hall-bar structure with perpendicularly magnetized current-injection electrodes

Spin-charge (SC) coupling is crucial in spintronics and the coupling mechanisms can be classified into bulk characteristic via spin-orbit interaction (SOI) or the interfacial characteristic provided by a junction formed by magnetic and nonmagnetic conductors. The two types of SC couplings account for the transverse resistance (TR) in a planer channel subjected to out-of-plane-polarized spin current injection. This is because interfacial spin-accumulation induces the diffusive transport of spin-angular momentum, which is converted into transverse charge accumulation via SOI. We explore the SC coupling characteristics of a lateral junction consisting of (i) a rare-earth transition metal (RE-TM) ferrimagnet with perpendicular magnetic anisotropy and (ii) a compensated metal, YH2, where electrons and holes simultaneously participate in spin and charge transports. This set-up allows us to observe the TR, which mirrors the magnetization of the RE-TM employed as the current-source electrode in the planer Hall-bar structure. The results show that the inverse spin Hall effect contributes significantly to the TR. Along with the TR measurement, we formulate a minimal expression of the TR when out-of-plane-polarized electron and hole spin currents are injected from the magnetic electrode. Since this formulation is independent of the details of the SC coupling mechanism, it is applied to interpret the observation result to reveal the SC coupling characteristics of the RE-TM and YH2 set-up.

Tunable surface magnetism by gate voltage in a slab of nonmagnetic half-Heusler compound CoTiSb.

The electrical manipulation of magnetization is appealing to the relevant experiment and spintronic device. In this paper, we focus on the electrical and magnetic properties of a thin film cleaved from the nonmagnetic half-Heusler compound CoTiSb. By means of the first-principles calculations, we find that the surface of TiSb termination possesses ferrimagnetism with a magnetic moment of 0.35 (0.49) μB per unit cell without (with) Hubbard U, which can persist below the Curie temperature of 48 (54) K. What is more, such a surface magnetism can be tuned to nonmagnetism by gate-induced hole doping with a concentration of 2.83 × 1014 (3.55 × 1014) cm-2. This magnetic tunability of the CoTiSb slab provides a platform to realize the pseudo-spin valve with both the magnetic electrodes and nonmagnetic space layer made of the same material without hetero-interfaces.