Large Magnetoresistance Values Research Articles

Giant tunnel magnetoresistance induced by thermal bias

We analyze the spin-resolved transport and, in particular, the tunnel magnetoresistance of an asymmetric ferromagnetic tunnel junction with an embedded quantum dot or molecule subject to thermal and voltage bias in the nonlinear response regime. We demonstrate that such system exhibits a giant tunnel magnetoresistance effect that can be tuned by gate and bias voltages. Large values of magnetoresistance are associated with the interplay between the Kondo correlations and the ferromagnetic-contact-induced exchange field. In particular, we show that the nonequilibrium current in the parallel and antiparallel magnetic configuration of the system changes sign at different values of the voltage and thermal bias. This gives rise to giant values of magnetoresistance, the sign of which can be controlled by the applied sources.

Large Magnetoresistance of Isolated Domain Walls in La2/3 Sr1/3 MnO3 Nanowires.

Generation, manipulation, and sensing of magnetic domain walls are cornerstones in the design of efficient spintronic devices. Half-metals are amenable for this purpose as large low field magnetoresistance signals can be expected from spin accumulation at spin textures. Among half metals, La1- x Srx MnO3 (LSMO) manganites are considered as promising candidates for their robust half-metallic ground state, Curie temperature above room temperature (Tc = 360 K, for x = 1/3), and chemical stability. Yet domain wall magnetoresistance is poorly understood, with large discrepancies in the reported values and conflicting interpretation of experimental data due to the entanglement of various source of magnetoresistance, namely, spin accumulation, anisotropic magnetoresistance, and colossal magnetoresistance. In this work, the domain wall magnetoresistance is measured in LSMO cross-shape nanowires with single-domain walls nucleated across the current path. Magnetoresistance values above 10% are found to be originating at the spin accumulation caused by the mistracking effect of the spin texture of the domain wall by the conduction electrons. Fundamentally, this result shows the importance on non-adiabatic processes at spin textures despite the strong Hund coupling to the localized t2g electrons of the manganite. These large magnetoresistance values are high enough for encoding and reading magnetic bits in future oxide spintronic sensors.

Double-Layer Kagome Metals Pt3Tl2 and Pt3In2

The connectivity and inherent frustration of the kagome lattice can produce interesting electronic structures and behaviors in compounds containing this structural motif. Here we report the properties of Pt3X2 (X = In and Tl) that adopt a double-layer kagome net structure related to that of the topologically nontrivial high-temperature ferromagnet Fe3Sn2 and the density wave hosting compound V3Sb2. We examined the structural and physical properties of single crystal Pt3Tl2 and polycrystalline Pt3In2 using X-ray and neutron diffraction, magnetic susceptibility, heat capacity, and electrical transport measurements, along with density functional theory calculations of the electronic structure. Our calculations show that Fermi levels lie in pseudogaps in the densities of states with several bands contributing to transport, and this is consistent with our Hall effect, magnetic susceptibility, and heat capacity measurements. Although electronic dispersions, characteristic of simple kagome nets with nearest-neighbor hopping, are not clearly seen, likely due to the extended nature of the Pt 5d states, we do observe moderately large and non-saturating magnetoresistance values and quantum oscillations in the magnetoresistance and magnetization associated with the kagome nets of Pt.

Enhancement of magnetoresistance with the variation of particle size in La0.68−xYxCa0.32MnO3, x = 0.0, 0.4, 0.5, 0.6

Huge magnetoresistance (MR) has been achieved in La0.68Ca0.32MnO3, by optimal substitution. To explore the origin of this giant enhancement of MR, we have carried out magnetic and magneto transport measurements of La0.68−xYxCa0.32MnO3, x = 0.0, 0.4, 0.5, 0.6 compounds in detail. Our analysis indicates that the disorder introduced by yttrium substitution plays the crucial role in the magneto resistive properties in this series. A large MR has been observed in optimally doped x = 0.5. In this compound, an MR value as high as 1.5 × 107% at a temperature of 50 K has been achieved for an external magnetic field of 90 kOe. The extraordinarily enhanced and large MR value has been described using a phenomenological model of percolation via ferromagnetic clusters. At the specific temperature sizes of these s compounds increases and MR% is likewise increased. For x = 0.6,not enough to create the percolation path.

Polycrystalline La0.66Gd0.04Ca0.3MnO3 for magnetic-response applications: concurrent anisotropic magnetoresistance and magneto-transport under a low magnetic field

Polycrystalline La0.66Gd0.04Ca0.3MnO3 with a large anisotropic magnetoresistance (−30%) value achieved under a magnetic field of 1 T.

Half-Metallic Heusler Alloy/MoS2 Based Magnetic Tunnel Junction.

Integration of half-metallic materials and 2D spacers into vertical magnetoresistive spin valves may pave the way for effective low-power consumption storage and memory technologies. Driven by the recent successful growth of graphene/half-metallic Co2Fe(Ge1/2Ga1/2) (CFGG) heterostructure, here we report a theoretical investigation of magnetic tunnel junction (MTJ) based on the ferromagnetic CFGG Heusler alloy and the MoS2 spacer of different thicknesses. Using ab initio approach, we demonstrate that the inherent ferromagnetism of CFGG is preserved at the interface, while its half-metallicity is recovering within few atomic layers. Ballistic transport in CFGG/MoS2/CFGG MTJ is studied within the nonequilibrium Green's function formalism, and a large magnetoresistance value up to ∼105% is observed. These findings support the idea of effective spintronics devices based on half-metallic Heusler alloys and highly diversified transition metal dichalcogenide family.

Large temperature coefficient of resistivity (TCR) of La1-xCaxMnO3 films prepared by spin-coating method

La1-xAxMnO3 (A = alkaline-earth or alkali metal) perovskites with large temperature coefficient of resistivity (TCR) offer immense opportunity for the application in high-performance infrared bolometer. However, numerous studies have revealed that the manganite films with large TCR values are not easily obtained by various fabrication technologies. Herein, a facile sol-gel spin-coating technique was used to prepare La1-xCaxMnO3 (LCMO, 0.280 ≤ x ≤ 0.375) films. All the samples were highly oriented along the out-of-plane direction of La0.3Sr0.7Al0.65Ta0.35O3 (001) substrates. With the rise in Ca doping amount, the resistivity of the films first decreased, and then, increased. This change can be attributed to the competition between the carrier concentration and lattice distortion. The LCMO films displayed large TCR and low-field magnetoresistance (MR) values, which exceeded those of previously reported thin films. The maximum TCR and low-field MR values were observed at x = 0.330, reaching 30.13% K−1 (266.43 K) and 68.6% (270.08 K), respectively. The La0.67Ca0.33MnO3 film with large TCR and MR values presents potential for the applications in high-sensitivity infrared bolometers and magnetic sensors.

Antiferromagnetic metallic state and low-temperature magnetoresistance in epitaxial La0.85Sr0.15MnO3 films

We report the magnetic coupling and magneto-transport properties of the epitaxial La0.85Sr0.15MnO3 films, which are fabricated on the (001)-oriented SrTiO3 substrate by RF magnetron sputtering. The anti-ferromagnetism and metallic state were observed in sequence, and both coexist below a critical temperature of 40 K. Meanwhile, the hysteresis loop exhibits the spin-flop transition. The antiferromagnetic phase originates from the A-type spin structure, in which the antiferromagnetic superexchange interaction between the adjacent MnO2 planes is along the c-axis direction. The metallic behavior stems from the double exchange interaction in the MnO2 plane in-plane. Furthermore, the spin scattering at phase boundaries between the ferromagnetic and antiferromagnetic phases causes a comparatively large magnetoresistance value of about −30% around 100 K. This effect, together with the colossal magnetoresistance, causes the large magnetoresistance values in a wide temperature range. This work helps to understand the magnetic coupling of the antiferromagnetic metallic state and magneto-transport properties in lightly doped manganite films.

The correlation between anisotropic magnetoresistance and phase separation in La0.4Pr0.3Ca0.3MnO3/NGO films

In this paper, the relationship between anisotropic magnetoresistance (AMR) and phase separation in La0.4Pr0.3Ca0.3MnO3 (LPCMO)/NGO films has been investigated. The films were grown on orthorhombic NGO (001) single crystal substrates by the pulsed laser deposition (PLD) method. The as-grown films were ex-situ annealed at 780 °C for 30 min in 400 mTorr oxygen pressures to clarify the effects of annealing on magnetoresistance (MR) and AMR. The X-ray diffraction (XRD) pattern confirmed that the substrate distance from the target is a key parameter for strong preferred crystallographic orientation growth. The temperature-dependent resistivity of the as-grown films revealed the coexistence of ferromagnetic and antiferromagnetic phases and the frozen glassy state at low temperatures. In the film with significant phase coexistence, the considerably large AMR and MR values of about 140% and 100% are achieved under the 5 kOe magnetic field. By tuning the target-substrate distance, different crystalline orientations of LPCMO can be obtained, and as a result, the metal-insulator transition (MIT) temperature, MR, and AMR can be modified.

Magnetoelectric and tunable DC electrical properties of PbZr0.58Ti0.42O3 – Ni0.5Co0.5Fe2O4 multiferroic nanocomposites

The potential properties of the magnetoelectric materials; such as magneto-impedance, magneto-dielectric, irreversibility of current with voltage and magnetoelectric coefficient provide a large research interest in the last few years. We have fabricated PbZr0.58Ti0.42O3 – Ni0.5Co0.5Fe2O4 nanocomposite having a 1:1 wt ratio through the low temperature pyrophoric chemical reaction and solid state reaction techniques. Structural characterization has been carried out through X-ray diffraction technique. We have investigated the magnetically tunable memory effect. The irreversibility in electrical property may be due to the interfacial polarization of the sample. The magnetic field provides a scattering of charge carriers resulting increment of current at a constant applied electric field. Furthermore, a large interfacial polarization of the sample attributes the current in the short circuit condition. Moreover, a large value of magnetoresistance has been found for the nanocomposite and it is ∼54% at a magnetic field of 3 kOe at room temperature.

Large magnetodielectric effect and negative magnetoresistance in NiO nanoparticles at room temperature.

Nickel oxide nanoparticles having a mean particle size of 19.5 nm were synthesized by a simple chemical method. Those nanoparticles exhibited a spin glass like behaviour at a temperature around 9 K. The samples showed electronic conduction arising out of small polaron hopping between the Ni2+ and Ni3+ species present in the material. A large magnetodielectric parameter with a maximum value of 52.2% was observed in the sample at room temperature which resulted from the Maxwell–Wagner polarization effect. This was explained as arising due to a large negative magnetoresistance caused by spin polarized electron hopping between Ni2+ and Ni3+ sites with the consequential formation of space charge polarization at the interfaces of the NiO nanoparticles. This was substantiated by direct measurement of magnetoresistance of the samples which gave identical results. It is believed that negative magnetoresistance after direct measurement occurred due to the interaction between ferromagnetic and antiferromagnetic phases and the value was 37%, the highest reported in the literature so far. As a result of the presence of Ni3+ ions, antiferromagnetic phase and ferromagnetic like behaviour of NiO nanoparticles gave higher magnetization than other reported nanoparticles. Such large values of magnetoresistance of the samples will make the material useful as an ideal magnetic sensor.

Magnetic field dependence of the martensitic transition and magnetocaloric effects in Ni49BiMn35In15

The structural, magnetic, and magnetocaloric properties of the Bi-doped Heusler alloy Ni49BiMn35In15 have been investigated using room temperature X-ray diffraction (XRD) and magnetization measurements in a temperature interval of 5-400 K. The alloy at room temperature was found to be in a mixture of a high temperature austenite phase (AP) and a low temperature martensite phase (MP). A drastic shift in the martensitic transition temperature at the rate of 16 K/T from 197 K to lower temperatures was observed. A kinetic arrest phenomenon of the AP was observed in the magnetization and electrical resistivity measurements during field-cooled (FC) measurements at 5T. A metamagnetic behavior characterized by a jump in magnetization in the isothermal M(H) curves near TM was observed. The maximum value of the magnetic entropy change and refrigerant capacity at Curie temperature were found to be 5.5 Jkg-1K-1 and 312 Jkg-1 for μoΔH = 5T, respectively. A large magnetoresistance value of -56% was found near the martensitic transition.

Magnetotransport phenomena and spin accumulation in MIS structures

The present work is devoted to magnetic transport in Fe/SiO2/p-Si, Mn/SiO2/p-Si and Fe3Si/p-Si hybrid structure. For Mn/SiO2/p-Si diode extremely large values of magnetoresistance were observed (105 % for AC and 107 % for DC) which is explained by impact ionization process that can be suppressed by the magnetic field. Lateral photovoltaic effect in Fe/SiO2/p-Si have also shown a strong dependence on the magnetic field in low-temperature region (the relative change of photovoltage exceeded 103 %). In Fe3Si/p-Si spin accumulation was found via 3-terminal Hanle measurements. We believe that the magnetic field affects electric transport through Lorentz force and through the interface states which are localized at the insulator/semiconductor or metal/semiconductor interfaces. Such states play a decisive role in magnetotrasnport as their energy can be controlled by a magnetic field. In Fe3Si/p-Si they also participate in spin-dependent tunneling, causing spin injection from the Fe3Si film into the silicon.

La0.67(Ca0.24Sr0.09)MnO3:xAg2O (0 ≤ x ≤ 0.25) composites with improved room–temperature TCR and MR for advanced uncooling infrared bolometers and magnetic sensors

In this research, high–density La0.67(Ca0.24Sr0.09)MnO3:xAg2O (LCSMO: xAg2O, x = 0, 0.05, 0.1. 0.15, 0.2, and 0.25) composites were successfully fabricated through the conventional sol-gel method. Scanning electron microscopy (SEM), X–ray photoelectron spectroscopy (XPS) and XRD data confirmed presence of silver at A sites (La3+/Ca2+/Sr2+) as Ag+ and segregates at grain boundaries (GBs) to form metallic silver. The electrical properties greatly improved by adding Ag2O. Significant enhancements in peak temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at room–temperature (300 K) were observed for LCSMO:xAg2O composites. The peak TCR increased from 3.7% K−1 (299.3 K, for x = 0) to 14.8% K−1 (301.0 K, for x = 0.2), and MR rose from 16.9% (303.0 K, for x = 0) to 34.1% (300.6 K, for x = 0.2). These improvements in peak TCR were attributed to increased grain size and formation of metallic silver at GBs or within the composites. Moreover, peak MR was higher in Ag2O doped composites, which was mainly due to large spin polarization effect and strong coupling ferromagnetic domains under external magnetic field. Overall, the large room-temperature TCR and MR values of LCSMO:0.2Ag2O composites look promising for future advanced uncooling infrared bolometers and magnetic sensors.

Quantization in magnetoresistance of strained InSb whiskers

Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentration 6·1016–6·1017 сm–3 was studied in the temperature range 4.2–40 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were observed in the strained and unstrained samples in all range of doping concentrations and magnetic fields. The character of longitudinal magnetoresistance dependences was analyzed and compared with theoretical one. The whisker magnetoresistance alters its sign with increasing magnetic field. It is positive at weak magnetic fields and becomes negative at higher magnetic fields. Possible mechanism of the large value of negative magnetoresistance (NMR) was discussed in the InSb whiskers with doping concentration in the vicinity to metal–insulator transition. The origin of large NMR was explained by the existence of classical size effect and boundary scattering during conductance in subsurface whisker layers.

Large Magnetocaloric Effect and Magnetoresistance in Fe and Co Co‐Doped Ni‐Mn‐Al Heusler Alloys

The Ni40Co10−xFexMn33Al17 (x = 4, 6, 8) alloys are prepared by arc‐melting method. The crystallographic structure, magnetic and magnetoresistance properties are systematically studied. The large magnetic change is obtained across the martensitic transformation from the ferromagnetic austenite phase to weak‐magnetic martensite phase. With the increase in Fe/Co ratio, the martensite transformation temperature shifts to the lower temperature. The large values of magnetoresistance of 33.3, 25.7, and 13.1% are achieved at the field of 3 T for x = 4, x = 6, and x = 8 alloys around the martensitic transformation, respectively. These results indicate that Ni‐Fe‐Co‐Mn‐Al alloy provides the motive power for further research in practical applications.

Probing the Fermi surface and magnetotransport properties of MoAs2

Transition metal dipnictides (TMDs) have recently been identified as possible candidates to host topology protected electronic band structure. These materials belong to an isostructural family and show several exotic transport properties. Especially, the large values of magnetoresistance (MR) and carrier mobility have drawn significant attention from the perspective of technological applications. In this report, we have investigated the magnetotransport and Fermi surface properties of single crystalline MoAs$_{2}$, another member of this group of compounds. Field induced resistivity plateau and a large MR have been observed, which are comparable to several topological systems. Interestingly, in contrast to other isostructural materials, the carrier density in MoAs$_{2}$ is quite high and shows single-band dominated transport. The Fermi pockets, which have been identified from the quantum oscillation, are largest among the members of this group and have significant anisotropy with crystallographic direction. Our first-principles calculations reveal a substantial difference between the band structures of MoAs$_{2}$ and other TMDs. The calculated Fermi surface consists of one electron pocket and another 'open-orbit' hole pocket, which has not been observed in TMDs so far.

Enhanced magnetoresistance in pulsed laser deposited stable chromium oxide thin films

Granular thin films of primarily rutile type tetragonal chromium dioxide (t-CrO2), along with a minor phase of hexagonal Cr2O3 were deposited on rutile type TiO2 layers by KrF excimer laser based pulsed laser deposition (PLD) technique using Cr2O3 targets. The TiO2 under-layer was also deposited by PLD process on oxidized Si substrates followed by annealing at 1100 °C for 10–15 min under O2 ambient. The lattice-matched interfacial TiO2 layer stabilizes the metastable Cr (IV) phase of CrO2, otherwise it readily converts into its stable phase of Cr (III) oxide, Cr2O3, under ambient conditions. Studies with X-ray diffraction (XRD) and Raman spectroscopy confirmed the stable t-CrO2 phase in the films. The microstructure in the films was studied with field emission scanning electron microscope (FESEM) and magnetic force microscope (MFM). As revealed by electrical analysis, the ferromagnetic (FM) t-CrO2 grains in conjunction with the antiferromagnetic (AFM) Cr2O3 phase in the tailored thin films effectively support an electrical transport process based on inter-granular spin-dependent tunneling (SDT) mechanism, giving rise to significantly high magnetoresistance (MR). A typical sample exhibits a markedly improved MR-value, viz., −30% at an applied field (H) of 438 kA/m at 278 K, than reported values in CrO2 thin films. Such a large MR value in the Coulomb blockade regime arises primarily not only because of the considerably suppressed spin flipping but also as a result of the highly effective SDT mechanism through an interlinked FM-AFM structure of chromium oxides in this specially engineered microstructure of the thin films. Such type of stable half-metallic thin films with low-H switching behavior is attractive for pertinent use in spintronics and magnetic sensing based applications.

Large positive magnetoresistance in intermetallic compound NdCo2Si2

The magnetic, magneto-transport and magnetocaloric properties of antiferromagnetic intermetallic compound NdCo2Si2(TN=32K) have been studied. The compound yields a positive magnetoresistance (MR) of about ∼123% at ∼5K in 8 T magnetic field. The MR value is significantly large vis – a – vis earlier reports of large MR in intermetallic compounds, and possibly associated with the changes in magnetic structure of the compound. The large MR value can be explained in terms of field induced pseudo-gaps on Fermi surface.

Molten salt route of La1 − xCaxMnO3 nanoparticles: Microstructural characterization, magnetic and electrical transport properties

Single-crystalline La1−xCaxMnO3 (LCMO, x=0.3 and 0.5) nanoparticles synthesized by molten salt method, have been studied based on their microstructural characterization, magnetic and electrical transport property measurements. X-ray diffraction patterns and electron diffraction patterns reveal that all the LCMO nanoparticles crystallize in the orthorhombic perovskite structure (Pnma space group). TEM images show that the LCMO nanoparticles exhibit irregular shapes and their particle sizes are increased with increasing the annealed temperatures. The resolved (200) lattice fringes in high-resolution TEM images confirm the single crystalline nature of the LCMO nanoparticles. Magnetization measurements versus temperature show a paramagnetic – ferromagnetic transition for all the nanoparticles. Room temperature and low temperature M – H loops demonstrate that the LCMO nanoparticles exhibit ferromagnetic behavior at 5K, whereas a paramagnetic behavior at 300K. Resistivity behavior of the LCMO nanoparticles demonstrate that they exhibit a broad metal — insulator (M−I) transition, and the transition temperature shifts towards a high temperature under an external magnetic field. The magnetoresistance (MR) values of the LCMO nanoparticles were increased monotonically with decreasing the temperature below 300K, and finally reached constant values at temperatures below 100K. The MR value of the La0.5Ca0.5MnO3 nanoparticles annealed at 650°C for 3h, was found to be 77% at 50K in 5T, and 57% for the La0.7Ca0.3MnO3 nanoparticles annealed at 650°C for 3h. Such large MR values of the present LCMO nanoparticles make them ideal candidates for the spintronic devices.