Maximum Magnetoresistance Ratio Research Articles

Tunnel Magnetoresistance-Based Sensor for Biomedical Application: Proof-of-Concept

The aim of this work was to investigate and prove the possibility of the real-time detection of magnetic nanoparticles (MNPs) distributed in solid material by using a tunnel magnetoresistance-based (TMR) sensor. Following the detection tests of FeCrNbB magnetic nanoparticles distributed in transparent epoxy resin (EPON 812) and measuring the sensor output voltage changes at different particle concentrations, the detection ability of the sensor was demonstrated. For the proposed TMR sensor, we measured a maximum magnetoresistance ratio of about 53% and a sensitivity of 1.24%/Oe. This type of sensor could facilitate a new path of research in the field of magnetic hyperthermia by locating cancer cells.

Giant tunneling magnetoresistance in in-plane double-barrier magnetic tunnel junctions based on MXene Cr2C.

The discovery of two-dimensional (2D) magnetic materials makes it possible to realize in-plane magnetic tunnel junctions. In this study, the transport characteristics of an in-plane double barrier magnetic tunnel junction (IDB-MTJ) based on Cr2C have been studied by density functional theory combined with the nonequilibrium Green's function method. The results showed its maximum tunneling magnetoresistance ratio (TMR) value reached 6.58 × 1010. Its minimum TMR value (3.86 × 106) was also comparable to those of conventional field effect transistors (FETs). Due to its giant TMR and unique structural characteristics, the IDB-MTJ based on Cr2C has great potential applications in magnetic random access memory (MRAM) and logic computing.

Room-temperature electrically tunable magnetoresistance behavior in graphene nanocrystalline

The electrically tunable magnetoresistance (MR) behavior of graphene-based devices at room temperature is becoming increasingly important in the development of continuously adjustable low-power-consumption magnetoelectronic applications. Herein, we design and construct an in-plane graphene nanocrystalline (GNC) film/n-Si device and observe a nonlinear S-shaped I–V curve, which lead to an electrically tunable MR behavior at near-room temperature. The MR value decreases gradually as the applied current increases, offering a switching ability with maximum high-low MR ratio (MR @1 μA/MR @3 mA) of ∼105%. A high MR (which is linearly related to the magnetic field strength) of ∼62% at 300 K is achieved by regulating the GNC grain size from 4 to 10 nm. The large, electrically tunable linear MR at room temperature in GNC film/n-Si devices have intriguing prospects for the fabrication of low-power-consumption sensitive logic and magnetic random-access memory MR devices.

Giant tunneling magnetoresistance in two-dimensional magnetic tunnel junctions based on double transition metal MXene ScCr2C2F2.

Two-dimensional (2D) transition metal carbides (MXenes) with intrinsic magnetism and half-metallic features show great promising applications for spintronic and magnetic devices, for instance, achieving perfect spin-filtering in van der Waals (vdW) magnetic tunnel junctions (MTJs). Herein, combining density functional theory calculations and nonequilibrium Green's function simulations, we systematically investigated the spin-dependent transport properties of 2D double transition metal MXene ScCr2C2F2-based vdW MTJs, where ScCr2C2F2 acts as the spin-filter tunnel barriers, 1T-MoS2 acts as the electrode and 2H-MoS2 as the tunnel barrier. We found that the spin-up electrons in the parallel configuration state play a decisive role in the transmission behavior. We found that all the constructed MTJs could hold large tunnel magnetoresistance (TMR) ratios over 9 × 105%. Especially, the maximum giant TMR ratio of 6.95 × 106% can be found in the vdW MTJ with trilayer 2H-MoS2 as the tunnel barrier. These results indicate the potential for spintronic applications of vdW MTJs based on 2D double transition metal MXene ScCr2C2F2.

Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin-filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study of two-dimensional materials has expanded to the field of spintronics. Intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 have received much attention due to their nearly spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design magnetic tunnel junctions (MTJs) of Cu/CrI3/Cu and Cu/CrBr3/Cu with electrodes of Cu(111) and a tunneling barrier of four-monolayer CrI3 or CrBr3. Our first-principle calculations combined with non-equilibrium Green’s function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin-filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that a negative differential resistance effect is observed in the CrBr3-based MTJ. The differences in spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the physics inside the device, including the spin-dependent density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJs.

Observation of magnetoresistance in CrI3/graphene van derWaals heterostructures* *Project supported by the National Natural Science Foundation of China (Grant No. 51872039) and Science and Technology Program of Sichuan, China (Grant No. M112018JY0025).

Two-dimensional ferromagnetic van der Waals (2D vdW) heterostructures have opened new avenues for creating artificial materials with unprecedented electrical and optical functions beyond the reach of isolated 2D atomic layered materials, and for manipulating spin degree of freedom at the limit of few atomic layers, which empower next-generation spintronic and memory devices. However, to date, the electronic properties of 2D ferromagnetic heterostructures still remain elusive. Here, we report an unambiguous magnetoresistance behavior in CrI3/graphene heterostructures, with a maximum magnetoresistance ratio of 2.8%. The magnetoresistance increases with increasing magnetic field, which leads to decreasing carrier densities through Lorentz force, and decreases with the increase of the bias voltage. This work highlights the feasibilities of applying two-dimensional ferromagnetic vdW heterostructures in spintronic and memory devices.

Butterfly-shaped magnetoresistance in triangular-lattice antiferromagnet Ag2CrO2

Spintronic devices using antiferromagnets (AFMs) are promising candidates for future applications. Recently, many interesting physical properties have been reported with AFM-based devices. Here we report a butterfly-shaped magnetoresistance (MR) in a micrometer-sized triangular-lattice antiferromagnet Ag2CrO2. The material consists of two-dimensional triangular-lattice CrO2 layers with antiferromagnetically coupled S = 3/2 spins and Ag2 layers with high electrical conductivity. The butterfly-shaped MR appears only when the magnetic field is applied perpendicularly to the CrO2 plane with the maximum MR ratio (≈15%) at the magnetic ordering temperature. These features are distinct from those observed in conventional magnetic materials. We propose a theoretical model where fluctuations of partially disordered spins with the Ising anisotropy play an essential role in the butterfly-shaped MR in Ag2CrO2.

Magnetic tunnel junctions with a B2 -ordered CoFeCrAl equiatomic Heusler alloy

The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for spin-gapless semiconductors (SGSs). However, to date, there have been no experimental attempts at fabricating a junction device. This paper reports a fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction measurements show that the (001) CoFeCrAl electrode films with atomically flat surfaces have a $B2$-ordered phase. The saturation magnetization is $380\phantom{\rule{0.16em}{0ex}}{\mathrm{emu}/\mathrm{cm}}^{3}$, almost the same as the value given by the Slater--Pauling--like rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87% and 165%, respectively. Cross-sectional electron diffraction analysis shows that the MTJs have MgO interfaces with fewer dislocations. The temperature- and bias-voltage-dependence of the transport measurements indicates magnon-induced inelastic electron tunneling overlapping with the coherent electron tunneling. X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state possessing SGS characteristics. Ab initio calculations taking account of the Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect of the Cr-Fe swap disorder on the ability for electronic states to allow coherent electron tunneling is discussed.

Spin transfer torque switching in exchange-coupled amorphous GdFeCo/TbFe bilayers for thermally assisted MRAM application

Exchange-coupled amorphous GdFeCo/TbFe memory layers in giant magneto-resistance (GMR) devices for spin transfer torque (STT) switching have been studied, and temperature dependence of the critical current density of the GMR devices was measured to discuss the effect of exchange-coupled bilayers as a memory layer of the thermally assisted magnetic random access memory (MRAM). The GMR devices having amorphous GdFeCo and TbFe memory bilayers with various thicknesses were prepared by magnetron sputtering and subsequent micro-fabrication processes. A pulsed current was applied to the GMR devices in order to investigate the spin transfer torque (STT) switching. The maximum magneto-resistance (MR) ratio was around 0.15%, and the coercivity of the memory bilayer increased with the TbFe thickness and decreased with elevating temperature. The critical current densities Jc to switch the memory bilayer with structure of Gd21.4 (Fe90Co10)78.6(9 nm)/Tb16Fe84 (1 nm) as low as 2.2 × 107 A cm−2 was obtained. The Jc reduced with increasing the temperature and was found to scale with the effective anisotropy Keff of GdFeCo/TbFe bilayer, which is believed to be suitable for the application of thermally assisted STT-MRAM.

The effect of door states on the magnetoresistance of a single-molecule electric revolving door-based spintronic device

By applying nonequilibrium Green’s functions in combination with density-function theory, the spin-dependent transport properties of a single-molecule electric revolving door-based spintronic device are investigated. The computational results show that magnetoresistance ratios are strongly dependent on the door states of the single-molecule electric revolving door. Under the application of a gate electric field, the single-molecule electric revolving door can be changed from the closed-door state to the open-door state, and thus the maximum magnetoresistance ratio of the corresponding spintronic device at finite bias can be improved from about 77% to about 4 104%. Therefore, the single-molecule electric revolving door will provide the possibilities for designing the high-performance single-molecule spin-valve device.

Superconductivity suppression in YBa2Cu3O7-δ/La0.7Sr0.3MnO3 bilayer films

We study the thickness effect of YBa2Cu3O7−δ (YBCO) in YBCO/La0.7Sr0.3MnO3 (LSMO) bilayer films, fabricated on LaAlO3 (001) substrate using pulsed laser deposition technique. The thickness dependent transport behavior of YBCO layer in considered bilayer systems demonstrate a clear onset critical temperature at 60 K and 80 K for 100 nm and 200 nm thick YBCO layer systems, respectively, whereas 50 nm thick YBCO system reveals complete suppression in the superconductivity. With the increase in thickness of YBCO layer, the magnetoresistance (MR) data show both positive and negative MR. The positive MR in superconducting regime dominates the negative MR, suppress the double exchange interaction. The maximum magnetoresistance ratio ∼81% at 64 K and ∼47% at 30 K temperature are observed for 200 nm and 100 nm YBCO layers, respectively. In YBCO(200 nm)/LSMO(200 nm) bilayer specimen, the temperature co-efficient of resistance is ∼8.4% K−1 at 72 K which can be practical for bolometric performances and temperature sensors.

Argon Ion Irradiation Effect on the Magnetic Properties of Fe-Al2O3 Nano Granular Film

We studied the effect of Argon (Ar) ion irradiation on Fe-Al2O3 nanogranular thin film. X-ray diffraction (XRD) patterns show that the ion dose might promote the growth of the Fe2O3 phase from an amorphous phase to a crystalline phase. The magnetic and magnetoresistance properties were investigated using a vibrating sample magnetometer (VSM) and a four point probe (FPP). The results suggest that percolation concentration occurred at the 0.55 Fe volume fraction and with a maximum magnetoresistance (MR) ratio of 3%. The present MR ratio was lower than that of previous results, which might be related to the existence of the α-Fe2O3 phase promoted by Ar ion irradiation. CEMS spectra show ion irradiation induces changes from superparamagnetic characteristics to ferromagnetic ones, which indicates the spherical growth of Fe particles in the Al2O3 matrix.

Strong ferromagnetism of reduced graphene oxide

The ferromagnetism of carbon-based materials has attracted much interest for its possible applications in spintronics devices. In this work, we studied the magnetic properties of reduced graphene oxide (rGO) obtained by high-temperature annealing of graphene oxide (GO) prepared in weak oxidizing conditions. The rGO samples exhibit strong room-temperature ferromagnetism, with saturation magnetization of 0.24 emu/g, about 24 times of the value of rGO prepared in strong oxidizing conditions. Hysteresis negative magnetoresistance (MR) has been observed in rGO, which confirms the intrinsic nature of the observed ferromagnetism. The MR value keeps nearly unchanged below 15 K, and decreases with further increasing temperature, and finally disappears at T ⩾ 50 K. At T = 5 K, the maximum MR ratio of [R(H) − R(0)]/R(0) is about −2.5%. The strong ferromagnetism is attributed to the preserved graphitic structure of weakly oxidized rGO, and the negative MR is due to the spin dependent scattering of defects.

Tunneling magnetoresistance effect in MnGa based perpendicular magnetic tunnel junction with Fe/Co interlayer

In order to enhance the magnetoresistance (MR) of perpendicular magnetic tunnel junctions (pMTJs) based on MnGa alloys, a single ferromagnetic layer such as Fe and Co was previously inserted between MnGa and MgO barrier. In this study, to further enhance the spin-filter effect, we introduced a Fe/Co bilayer as an interlayer in the MnGa/MgO interface. Compared to the single Co interlayer, an apparent MR ratio enhancement was obtained when Fe layer thickness was around 0.3 nm for pMTJs with MnGa compositions of Mn57Ga43, Mn62Ga38, and Mn70Ga30, and the maximum MR ratio reaches 50% at room temperature. In addition, inverted magnetoresistance loops were observed due to the antiparallel alignment of the magnetic moments of Co and MnGa layers separated by the thin Fe layer.

Electrical and magneto-transport properties of ferromagnet/superconductor/ferromagnet based heterostructure

La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 (LSMO/YBCO/LSMO) heterostructures were prepared by pulsed laser deposition technique. The resistivity–temperature (ρ–T) variation and magnetoresistance effects of these heterostructures have been studied and are found to be dependent on the thickness of superconducting spacer layer. We have observed that metal–insulator (TMI) transition get suppressed with increase in thickness of the spacer layer. The maximum magnetoresistance ratio ∼70% at 266K and ∼65% at 254K temperature are observed for 50nm and 100nm spacer layers respectively. In LSMO(200nm)/YBCO(50nm)/LSMO(200nm) specimen the temperature coefficient of resistance (TCR) is ∼6.63%K−1 which can be useful for bolometric performances and temperature sensors.

Structural, Magnetic, and Transport Properties of La0.62Sb0.38MnO3 Ceramic

The polycrystalline La0.62Sb0.38MnO3 sample has been prepared by the solid-state reaction method. Structural, magnetic and electrical transport properties have been researched. X-ray diffraction analysis confirms the hexagonal crystal symmetry. Magnetization measurements indicate La0.62Sb0.38MnO3 experienced from paramagnetic to ferromagnetic state transition with decreasing temperature at about 225 K. Resistivity dependences on temperature exhibit metal-insulator transition (MIT), and the maximum magnetoresistance (MR) ratio is about 33 % at temperature of 189 K and magnetic field of 2 T.

Effects of lattice deformation on magnetic properties of electron-doped La0.8Hf0.2MnO3 thin films

The lattice deformation effects on electric and magnetic properties of electron-doped La0.8Hf0.2MnO3 (LHMO) thin films have been systematically investigated. LHMO films with various thicknesses (15 nm, 40 nm, and 80 nm) were grown on (001) SrTiO3 and (001) LaAlO3 substrates, which induces in-plane tensile and compressive biaxial stress, respectively. The metal-insulator phase transition temperature (TP) and magnetoresistance (MR) effect show a strong dependence on film thickness. TP increases with a decrease in thickness and is enhanced as the lattice strain rises, regardless of whether it is tensile or compressive. The maximum MR ratio is suppressed by reduction of the film thickness. These anomalous phenomena may be attributed to the competition between the strain induced modification of the Mn-O bond length and the eg orbital stability.

Strain-induced magnetoresistance and magnetic anisotropy properties of Co/Cu multilayers

[Co (tCo) nm/Cu 1.5 nm]50 multilayers were grown onto 15-nm Cu/polyimide buffer layers. The relationship between stress, σ, and strain, ɛ, for the [Co 1.0 nm/Cu 1.5 nm]50 multilayers has been presented. The effects of induced strain on the magnetoresistance (MR) and magnetic anisotropy have been examined. The [Co 1.0 nm/Cu 1.5 nm]50 multilayer exhibited a maximum MR ratio of 3.4% at a Co layer thickness of 1.0 nm, β of 0.1, and a strain of 1.5%. The multilayers exhibited a remarkable magnetic anisotropy with the easy axis of magnetization always lying in a plane perpendicular to the direction of the induced strain.

Magnetic Field Effect on Photoconductivity of Single-Crystalline Pentacene and Perfluoropentacene Field-Effect Transistors

ABSTRACTOrganic magnetoresistance (OMAR) of single-crystalline (SC) pentacene (C22H14) and perfluoropentacene (C22F14) was studied using field-effect transistor structures. The gate voltage effect showed that the OMAR originates from photo-induced current and requires both electrons and holes in the transport channel. The temperature dependence showed the maximum magnetoresistance (MR) ratio up to -6% under light irradiation at approximately 200 K and magnetic field of 80 mT. The charge carrier mobility and the exciton diffusion length were not important factors to determine the MR ratios. The interaction between triplet excitons and traps was thought to govern the OMAR behaviors.

Tunneling Magnetoresistance (TMR) on Fe-Al<sub>2</sub>O<sub>3</sub> Nano Granular Film Growth by Helicon Plasma Sputtering

Fe-Al 2 O 3 nanogranular thin film by helicon plasma sputtering with the variation of Fe content from 0.1 to 0.7 volume fraction have been prepared. The magnetic and magnetoresistance properties were investigated by a Vibrating Sample Magnetometer (VSM) and a Four Point Probe (FPP). The Rutherford BackScattering (RBS) was performed with the SIMNRA software. Conversion Electron Mossbauer Spectroscopy (CEMS) study was also performed to estimate the fraction of Fe and α-Fe 2 O 3 in the granular film. The results suggested that the percolation concentration occured at 0.55 Fe volume fractions, with the maximum Magnetoresistance (MR) ratio of 3%. The present MR ratio that was lower than the previous results may be related to the existence of α-Fe 2 O 3 phase.