Huge Magnetoresistance Effect Research Articles

High-Mobility Topological Semimetals as Novel Materials for Huge Magnetoresistance Effect and New Type of Quantum Hall Effect.

The quantitative description of electrical and magnetotransport properties of solid-state materials has been a remarkable challenge in materials science over recent decades. Recently, the discovery of a novel class of materials-the topological semimetals-has led to a growing interest in the full understanding of their magnetotransport properties. In this review, the strong interplay among topology, band structure, and carrier mobility in recently discovered high carrier mobility topological semimetals is discussed and their effect on their magnetotransport properties is outlined. Their large magnetoresistance effect, especially in the Hall transverse configuration, and a new version of a three-dimensional quantum Hall effect observed in high-mobility Weyl and Dirac semimetals are reviewed. The possibility of designing novel quantum sensors and devices based on solid-state semimetals is also examined.

Огромное магнетосопротивление в структуре металл--органический полупроводник--металл

The article represents results of huge magnetoresistance effect investigation in the structure of magnetic metal / organic semiconductor / nonmagnetic metal with magnitude of ~ 2600%. There are observed influence of magnetic field on concentration and mobility of charge carriers and on magnitude of ferromagnetic/semiconductor potential barrier. Theoretical interpretation is considered with previously discussed model. The model describes influence of hyperfine fields on spin selective hopping rate between the sites in the polymer

Effect of Etching Time to Tune Magnetoresistance Between Positive and Negative Values in p-Type Silicon Nanowires

Silicon nanowires (SiNWs) are formed by metal-assisted chemical etching of crystalline p-type silicon, in a mixture of aqueous HF and AgNO3 chemical solutions. The magnetic field effects on the current of Ag/SiNWs/Si/Al structures have been studied. At room temperature, magnetoresistance (MR) measurements revealed positive and negative MR depending on the etching time and on the applied voltage. Huge positive MR of about 1200% has been observed at the low field. The negative MR is attributed to the weak localization effect, while the positive one is related to the ohmic regime, where holes control the current. The MR effect depends on the applied voltage and on the SiNWs length. The huge MR effect on SiNWs can be exploited in magnetic-field sensor devices.

Helicity-Protected Domain-Wall Magnetoresistance in Ferromagnetic Weyl Semimetal

The magnetotransport properties of disordered ferromagnetic Weyl semimetals are investigated numerically. We found an extraordinarily stable and huge magnetoresistance effect in domain walls of Weyl semimetals. This effect originates from the helicity mismatch of Weyl fermions and is a specific property of Weyl semimetals. Although conventional magnetoresistance effects are strongly suppressed in domain walls where local magnetization varies gradually, the helicity-protected magnetoresistance in Weyl semimetals maintains almost $100\%$ of the magnetoresistance ratio for any kind of thick domain walls, even in the presence of disorder. The contribution of surface Fermi arcs to the magnetoresistance is also discussed.

Giant Tunnel Magnetoresistance with a Single Magnetic Phase-Transition Electrode

Magnetic phase transition tunnel magnetoresistance (MPT-TMR) effect with a single magnetic electrode has been investigated by first-principles calculations. The calculations show that the MPT-TMR of FeRh/MgO/Cu tunnel junction can be as high as hundreds of percent when the magnetic structure of FeRh changes from G-type antiferromagnetic (GAFM) to ferromagnetic order. This new type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance because of its huge magneto-resistance effect and similar structural simplicity. The main mechanism for the giant MPT-TMR can be attributed to the formation of interface resonant states at GAFM-FeRh/MgO interface. A direct FeRh/MgO interface is found to be necessary for achieving high MPT-TMR experimentally. Moreover, we find the FeRh/MgO interface with FeRh in ferromagnetic phase has nearly full spin-polarization due to the negligible majority transmission and significantly different Fermi surface of two spin channels. Thus, it may act as a highly efficient and tunable spin-injector. In addition, electric field driven MPT of FeRh-based hetero-magnetic nanostructures can be utilized to design various energy efficient tunnel junction structures and the corresponding lower power consumption devices. Our results will stimulate further experimental investigations of MPT-TMR and other fascinating phenomenon of FeRh-based tunnel junctions that may be promising in antiferromagnetic spintronics.

Huge magnetoresistance induced by half-metal-semiconductor phase transition in a one-dimensional spin chain: a first-principles study.

In experimental studies, magnetoresistance (MR) values of 103 are hard to reach for conventional single-molecule spin-valves. Motivated by a recent experiment [Nano Lett., 2016, 16, 577-582], where tailored Co-salophene-based all-spin molecular devices are successfully realized, we demonstrate the functionality of a Co-salophene-based spin chain without magnetic electrodes. By using nonequilibrium Green's functions in combination with density functional theory, we find that the maximum MR ratio of this spin chain can reach 106 by manipulating its spins in a controlled way, which is several orders of magnitude higher than previously reported experimental values. As the Co-salophene-based spin chain has been successfully synthesized, we are highly expectant of the experimental realization of huge MR ratios.

Huge magnetoresistance and low junction resistance in magnetic tunnel junctions with crystalline MgO barrier

Inserting a 4 /spl Aring/-Mg metal layer between the amorphous CoFeB bottom electrode layer and the MgO barrier layer was found to be effective in realizing huge magnetoresistance effect in low-resistance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). As a result, magnetoresistance (MR) ratio as high as 138% at resistance-area product (RA) of about 2.4 /spl Omega//spl middot//spl mu/m/sup 2/ was obtained. This value is about seven times that of state-of-the-art MTJs for magnetic sensor application. X-ray diffraction analysis clarified that crystal orientation of the poly-crystalline MgO(001) barrier layer was improved by the Mg layer. It is suggested that the higher crystalline orientation of the MgO(001) barrier layer could have enhanced the coherent tunneling of /spl Delta//sub 1/ electrons, resulting in an increase of MR ratio at the low RA (thin MgO thickness) region. The annealing temperature and free layer materials have also been optimized to satisfy the requirements for practical read head application. Although this optimization resulted in a reduction in the MR ratio to about 45%-53%, this value is still more than twice the highest MR ratio of conventional MTJs. The currently developed fabrication process will accelerate the development of highly sensitive read heads for ultrahigh-density hard-disk drives.

Magnetic-Field-Sensing Materials Composed of Metal–Semiconductor Hybrid Nanostructures

A huge positive magnetoresistance effect, about 4 orders of magnitude at room temperature, was discovered in metal-semiconductor hybrid nanostructures. The hybrid material consisting of metallic nanostructures that are fabricated on a GaAs substrate by ultra-high vacuum deposition method exhibits magnetic field-sensitive current-voltage characteristics. When a constant voltage above the threshold value, is applied to the film, a very steep change in the current, which we term magnetoresistive switch, is driven by the huge magnetoresistance effect under a relatively low magnetic field at room temperature. The magnetoresistance effect is very sensitive to the nanoscale morphology of the hybrid film; in other words, one can control the magnetoresistance function at will by modifying the nanostructure of this material. The origin of the magnetoresistive switch effect and its possible application as a magnetic field sensor is discussed.

Room temperature magnetoresistance effect observed in Au/GaAs films processed by focused ion beam

Abstract Huge magnetoresistance (MR) effect was observed in Au/GaAs films with a nano-size trench fabricated by a focused ion beam process. Positive MR effect with the ratio of 32,000% was obtained in the magnetic field of 15,000 Oe at room temperature. This huge MR effect is promising for the application to spintronic devices such as magnetic sensors.

Huge magnetoresistance effect of highly oriented pyrolytic graphite

Graphite is a quasi-two-dimensional semimetal. However, for usual graphite the magnetoresistance is not so high due to its small crystal size and no preferred orientation. Huge positive magnetoresistance up to 85300% at 4.2 K and 4950% at 300 K under 8.15 T magnetic field was found in highly oriented pyrolytic graphite. The mechanism of huge positive magnetoresistance is not only due to ordinary magnetoresistance but also due to magnetic-field-driven semimetal-insulator transition.

Metal-nanocluster equipped GaAs surfaces designed for high-sensitive magnetic field sensors

A huge positive magnetoresistance (MR) effect, more than 10 5% at room temperature (RT), has been discovered in metal-nanocluster equipped GaAs surfaces. Granular film consisting of nanoscale MnSb metal-clusters that are grown on a sulfur-terminated GaAs(0 0 1) substrate by molecular-beam epitaxy exhibits magnetic-field-sensitive current–voltage characteristics. When a constant voltage, above the threshold value, is applied to the film, very steep change in the current, which we term magnetoresistive switch, is driven by the huge MR effect under a relatively low magnetic field at RT. The origin of the magnetoresistive switch effect is discussed in terms of a novel concept of magnetic-field-sensitive avalanche breakdown. These properties strongly depend on the morphological condition of metal-nanoclusters, and seem to depend on electronic properties of the GaAs surface.

Magnetoresistive switch effect in metal/semiconductor hybrid granular films: extremely huge magnetoresistance effect at room temperature

Hybrid granular films, consisting of nanoscale metal clusters that are grown on a GaAs substrate by molecular beam epitaxy, exhibit magnetic-field-sensitive current–voltage (I–V) characteristics at room temperature. When a constant voltage, above the threshold value, is applied to the film, the I–V curve becomes nonlinear and a breeding-like current increase appears. The abrupt increase disappears with the application of magnetic fields, which we call the magnetoresistive switch. The switch yields the huge positive magnetoresistance effect, for example 320 000% at 2 kOe. The origin of the magnetoresistive switch effect is discussed in terms of a magnetic-field dependence of an avalanche breakdown.

Magnetoresistive switch effect in metal/semiconductor hybrid granular films—extra huge magnetoresistance effect at room temperature

A granular film consisting of nanoscale metal clusters that are grown on a GaAs substrate by molecular-beam epitaxy exhibits magnetic-field-sensitive current–voltage characteristics at room temperature. When a constant voltage, above the threshold value, is applied to the film, a steep current-increase appears. The abrupt increase disappears on applying magnetic fields, which we term magnetoresistive switch. The switch yields a huge positive magnetoresistance effect, 320 000% at 2000 Oe.

Magnetoresistive switch effect in MnSb granular films grown on sulfur-passivated GaAs: more-than 10 000% magnetoresistance effect at room-temperature

A huge positive magnetoresistance effect, more than 10 000% at room temperature, has been discovered in MnSb granular films. Granular films consisting of nanoscale MnSb dots were fabricated on a sulfur-passivated GaAs (0 0 1) substrate by molecular-beam epitaxy, then covered with an Sb thin layer. The MnSb granular films exhibit a strong in-plane anisotropy of the magnetic-field-sensitive current–voltage characteristics. When a constant voltage, above the threshold value, is applied in the [1 1 0] direction of the GaAs (0 0 1) surface, a steep change in the current, which we term magnetoresistive switch (MRS), is driven by the huge magnetoresistance effect under a relatively low magnetic field (less than about 0.2 T ). On the other hand, less than 1% magnetoresistance effect was observed when the voltage was applied in the [1 1 ̄ 0] direction of the GaAs surface. The origin of the anisotropy is discussed in terms of the microscopic structural anisotropy at the heterointerface.