In solid state physics, giant magnetoresistance is the large change in electrical resistance due to an external magnetic field. Here we show that giant magnetoresistance is possible in a spin chain composed of weakly interacting layers of strongly coupled spins. This is found for all system sizes even down to a minimal system of four spins. The mechanism driving the effect is a mismatch in the energy spectrum resulting in spin excitations being reflected at the boundaries between layers. This mismatch, and thus the current, can be controlled by external magnetic fields resulting in giant magnetoresistance. A simple rule for determining the behavior of the spin transport under the influence of a magnetic field is presented based on the energy levels of the strongly coupled spins.
The electronic and magnetic properties of SrFeO$_{3-δ}$ single crystals with controlled oxygen content ($0 \leq δ\leq 0.19$) have been studied systematically by susceptibility, transport and spectroscopic techniques. An intimate correlation between the spin-charge ordering and the electronic transport behavior is found. Giant negative as well as positive magnetoresistance are observed.
For high-mobility two-dimensional electrons at a GaAs/AlGaAs heterojunction, we have studied, both experimentally and theoretically, the recently discovered giant magnetoresistance oscillations with nearly zero resistance in the oscillation minima which appear under microwave radiation. We have proposed a model based on nonequilibrium occupation of Landau levels caused by radiation which describes the oscillation picture.
We report the structural, magnetic, exchange bias and magnetotransport effect in Sr$_{4}$Fe$_{3}$CoO$_{11}$. The material crystallizes in the orthorhombic $\textit{Cmmm}$ space group. It shows antiferromagnetic (G-type) transition (T$_{N}$ = 255 K) along with interesting temperature induced magnetization reversal (T$_{Comp.}$= 47 K measured at 100 Oe). The magnetic reversal can be elucidated considering the increased magnetocrystalline anisotropy with Co substitution. Magnetoresistance measurements shows an interesting crossover from negative to positive side at $\sim$ 100 K. The negative magn…
At low temperature and for finite spin scattering in a weakly disordered metal, for a certain value, predicted from our theory, of the material-dependent paramagnon interaction, the total conductivity becomes highly sensitive to the orbital effects of a finite magnetic field. As a consequence, positive giant magnetoresistance and giant corrections to the Hall coefficient arise. We obtain very good agreement between this theory and recent positive giant magnetoresistance experiments, while making specific material-dependent predictions.
We report on giant positive magnetoresistance effect observed in VOx thin films, epitaxially grown on SrTiO3 substrate. The MR effect depends strongly on temperature and oxygen content and is anisotropic. At low temperatures its magnitude reaches 70% in a magnetic field of 5 T. Strong electron-electron interactions in the presence of strong disorder may qualitatively explain the results. An alternative explanation, related to a possible magnetic instability, is also discussed.
Magnetization and magnetoresistance measurements are reported for antiferromagnetically coupled DyFe$_2$/YFe$_2$ multilayers in fields up to 23 T. We demonstrate that the formation of short exchange springs (~ 2 nm) in the magnetically soft YFe$_2$ layers results in a giant magneto-resistance as high as 32% in the spring region. It is shown that both the magnitude of the effect, and its dependence on magnetic field, are in good agreement with the theory of Levy and Zhang for giant magnetoresistance due to domain wall like structures.
We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density {\it quasi}-two dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the {\it orbital} motion arising from the {\it finite} layer thickness and the large Fermi wavelength of the {\it quasi}-two dimensional system at low carrier densities.
We report room temperature giant baro-resistance ($\approx$128\%) in $Fe_{49}(Rh_{0.93}Pd_{0.07})_{51}$. With the application of external pressure and magnetic field the temperature range of giant baro-resistance ($\approx$600\% at 5K and 19.9 kbar and 8 Tesla) and magnetoresistance ($\approx$-85\% at 5K and 8 tesla) can be tuned from 5 K to well above room temperature. As the AFM state is stabilized at room temperature under external pressure, it shows giant room temperature magnetoresistance ($\approx$-55\%) with magnetic field. Due to coupled magnetic and latticel changes, the isothermal ch…
The results of dc magnetization, electrical and magnetoresistance and heat capacity measurements (2-300 K) on Tb7Rh3, crystallizing in Th7Fe3-type hexagonal structure, are reported. In this compound, magnetic ordering sets in around 90 K with additional transitions at low temperatures and the temperature coefficient of resistivity (R), dR/dT, is negative over a wide temperature range in the paramagnetic state. The present magnetization results reveal that this compound is apparently characterized by rich features in the magnetic-field-temperature phase diagram. A point of major emphasis is tha…
MBE-grown, 5 nm-thick annealed Ga0.95Mn0.05As films with Tc~90K demonstrate transition from metallic to insulating state below To~10K, where sheet resistances Rsh~h/e2 and both longitudinal Rxx and transverse Rxy components become comparable. Below metal-insulator transition we found giant anisotropic magnetoresistance (GAMR), which depends on orientation of magnetization to crystallographic axes and manifests itself in positive magnetoresistance near 50% for Rxx at T=1.7K, H//[110] crystallographic direction and parallel to current in contrast to smaller and negative magnetoresistance for H//…
We study the giant magnetoresistance of nanogranular magnets in the presence of an external magnetic field and finite temperature. We show that the magnetization of arrays of nanogranular magnets has hysteretic behaviour at low temperatures leading to a double peak in the magnetoresistance which coalesces at high temperatures into a single peak. We numerically calculate the magnetization of magnetic domains and the motion of domain walls in this system using a combined mean-field approach and a model for an elastic membrane moving in a random medium, respectively. From the obtained results, we…
We use numerically unbiased methods to show that the one-dimensional Hubbard model with periodically distributed on-site interactions already contains the minimal ingredients to display the phenomenon of magnetoresistance; i.e., by applying an external magnetic field, a dramatic enhancement on the charge transport is achieved. We reach this conclusion based on the computation of the Drude weight and of the single-particle density of states, applying twisted boundary condition averaging to reduce finite-size effects. The known picture that describes the giant magnetoresistance, by interpreting …
In the present work we reply to the Comment by Catalan and Scott (cond-mat/0607500) on two of our papers. This Comment has been rejected from publication in Physical Review Letters and, hence, our Reply is based on the cond-mat version.
We report the discovery of giant and anisotropic magnetoresistance due to the orbital rearrangement in a non-magnetic correlated metal. In particular, we measured the magnetoresistance under fields up to 31.4 T in the cubic Pr-based heavy fermion superconductor PrV$_2$Al$_{20}$ with a non-magnetic $Γ_3$ doublet ground state, exhibiting antiferro-quadrupole ordering below 0.7 K. For the [100] direction, we find that the high-field phase appears between 12 T and 25 T, accompanied by a large jump at 12 T in the magnetoresistance ($ΔMR \sim $ 100 $\% $) and in the anisotropic magnetoresistivity (A…
Disorder-induced magnetoresistance has been reported in a range of solid metals and semiconductors, however, the underlying physical mechanism is still under debate because it is difficult to experimentally control. Liquid metals, due to lack of long-range order, offers an ideal model system where many forms of disorder can be deactivated by freezing the liquid. Here we report non-saturating magnetoresistance discovered in the liquid state of three metals: Ga, Ga-In-Sn and Bi-Pb-Sn-In alloys. The giant magnetoresistance appears above the respective melting points and has a maximum of 2500% at …
We have studied the electron transport in SiO${}_2$(Co)/GaAs and SiO${}_2$(Co)/Si heterostructures, where the SiO${}_2$(Co) structure is the granular SiO${}_2$ film with Co nanoparticles. In SiO${}_2$(Co)/GaAs heterostructures giant magnetoresistance effect is observed. The effect has positive values, is expressed, when electrons are injected from the granular film into the GaAs semiconductor, and has the temperature-peak type character. The temperature location of the effect depends on the Co concentration and can be shifted by the applied electrical field. For the SiO${}_2$(Co)/GaAs heterost…
Two-dimensional magnetic materials have recently attracted great interest due to their unique functions as the electric field control of a magnetic phase and the anomalous spin Hall effect. For such remarkable functions, a spin-orbit coupling (SOC) serves as an essential ingredient. Here we report a giant positive magnetoresistance in a layered magnetic semiconductor AgCrSe2, which is a manifestation of the subtle combination of the SOC and Zeeman-type spin splitting. When the carrier concentration approaches the critical value of 2.5\times10^18 cm^-3, a sizable positive magnetoresistance of ~…
We have studied anisotropic magnetoresistance (MR) and magnetization with rotating magnetic field (B) within $CuO_2$ plane in lightly doped AF $Nd_{2-x}Ce_xCuO_{4}$. \emph{A giant anisotropy} in MR is observed at low temperature below 5 K. The c-axis resistivity can be tuned about one order of magnitude just by changing B direction within $CuO_2$ plane and a scaling behavior between out-of-plane and in-plane MR is found. A "Spin valve" effect is proposed to understand the giant anisotropy of out-of-plane MR and the evolution of scaling parameters with the external field. It is found that the f…
We present microscopic results on the giant tunneling magnetoresistance that arises from the nanoscale coexistence of ferromagnetic metallic (FMM) and antiferromagnetic insulating (AFI) clusters in a disordered two dimensional electron system with competing double exchange and superexchange interactions. Our Monte Carlo study allows us to map out the different field regimes in magnetotransport and correlate it with the evolution of spatial structures. At coexistence, the isotropic O(3) model shows signs of slow relaxation, and has a high density of low energy metastable states, but no genuine …
We report here the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to Pm-3m space group. The sample is found to be paramagnetic down to 2 K with metallic character. On application of magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows negative temperature coefficient of resistivity below about 50 K under the application of field gretare than or …
The LAO/STO interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70\%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20~K range --- indicative of a single-particle mechanism. Motivated by a striking correspondence bet…
The magnetic and magnetotransport properties of the Sr3Fe2-xCoxO7-d system (0.2 <= x <= 1.0) were systematically investigated. This oxide system exhibits a giant magnetoresistance (GMR) effect at low temperatures, reaching up to 80% in 7 T at 5 K. Ac-susceptibility measurements show that there exists a strong competition between ferromagnetic (F) and spin glass states, and the balance between these two magnetic states can be controlled by varying cobalt (x) and/or oxygen contents (d). Importantly, the MR effect is closely related to the magnetic property: the development of magnetic disorderin…
Effect of Ge substitution on first order ferrimagnetic (FRI) - antiferromagnetic (AFM) transition in Mn$_2$Sb has been studied. It shows that transition temperature (T$_t$) can be tuned between 119~K - 271~K by substituting 2.5-10\% Ge at Sb site in Mn$_2$Sb. The variation of density of state at Fermi level N(E$_f$) with Ge substitution shows that dN(E)/dE is positive at E$_f$ in the AFM state. With the application of magnetic field T$_t$ shifts to low temperature, which results in a giant negative magnetoresistance (MR) reaching a value of 70\% for 2.5\% substitution. Our results show that FR…
The magnetic, thermodynamic and electrical/thermal transport properties of the caged-structure quasi-skutterudite Gd$_3$Ir$_4$Sn$_{13}$ are re-investigated. The magnetization $M(T)$, specific heat $C_p(T)$ and the resistivity $ρ(T)$ reveal a double-phase transition -- at $T_{N1}\sim$ 10~K and at $T_{N2}\sim$ 8.8~K -- which was not observed in the previous report on this compound. The antiferromagnetic transition is also visible in the thermal transport data, thereby suggesting a close connection between the electronic and lattice degrees of freedom in this Sn-based quasi-skutterudite. The temp…
We investigated the magnetoresistance (MR) effect of the pyrochlore oxide Nd2Ir2O7, which shows a metal-insulator transition at T_MI =33 K. A small positive MR effect was observed in the metallic state above T_MI, while a large negative MR effect was observed in the insulating state below T_MI . MR effects exceeding 3000% were found at 1 K at a field of 9 T. As a result, we confirmed the crossover from the insulating state to a state with a small or partial band gap in a field up to 56 T. Furthermore, from the MR effect in Eu2Ir2O7 (T_MI = 120 K) and Gd$_2$Ir$_2$O$_7$ (T_MI = 127 K), we reveal…
Dirac semimetals and Weyl semimetals are 3D analogs of graphene in which crystalline symmetry protects the nodes against gap formation [1-3]. Na$_3$Bi and Cd$_3$As$_2$ were predicted to be Dirac semimetals [4,5], and recently confirmed to be so by photoemission [6-8]. Several novel transport properties in a magnetic field $\bf H$ have been proposed for Dirac semimetals [2,9-11]. Here we report an interesting property in Cd$_3$As$_2$ that was unpredicted, namely a remarkable protection mechanism that strongly suppresses back-scattering in zero $\bf H$. In single crystals, the protection results…
The extremely large transverse magnetoreistance (the magnetoresistant ratio $\sim 1.3\times10^5\%$ in 2 K and 9 T field, and $4.3\times 10^6\%$ in 0.4 K and 32 T field, without saturation), and the metal-semiconductor crossover induced by magnetic field, are reported in NbSb$_2$ single crystal with electric current parallel to the $b$-axis. The metal-semiconductor crossover is preserved when the current is along the $ac$-plane but the magnetoresistant ratio is significantly suppressed. The sign reversal of the Hall resistivity in the field close to the crossover point, and the electronic struc…
We report on systematic temperature- and magnetic field-dependent studies of the EuGa$_4$ binary compound, which crystallizes in a centrosymmetric tetragonal BaAl$_4$-type structure with space group $I4/mmm$. The electronic properties of EuGa$_4$ single crystals, with an antiferromagnetic (AFM) transition at $T_\mathrm{N} \sim 16.4$ K, were characterized via electrical resistivity and magnetization measurements. A giant nonsaturating magnetoresistance was observed at low temperatures, reaching $\sim 7 \times 10^4$ % at 2 K in a magnetic field of 9 T. In the AFM state, EuGa$_4$ undergoes a seri…
A spin-$\frac{1}{2}$ subsystem conjoined along a cut with a subsystem of spinless fermions in the state of topological insulator is studied on a honeycomb lattice. The model describes a junction between a 2D topological insulator and a 2D spin lattice with direction-dependent exchange interactions in topologically trivial and nontrivial phase states. The model Hamiltonian of the complex system is solved exactly by reduction to free Majorana fermions in a static $\mathbb{Z}_2$ gauge field. In contrast to junctions between topologically trivial phases, the junction is defined by chiral edge stat…
The oscillatory magnetoresistance spectrum of the organic metal (BEDO)$_5$Ni(CN)$_4\cdot$3C$_2$H$_4$(OH)$_2$ has been studied up to 50 T, in the temperature range from 1.5 K to 4.2 K. In high magnetic field, its Fermi surface corresponds to a linear chain of quasi-two-dimensional orbits coupled by magnetic breakdown (MB). The scattering rate consistently deduced from the data relevant to the basic $α$ and the MB-induced $β$ orbits is very large which points to a significant reduction of the chemical potential oscillation. Despite of this feature, the oscillations spectrum exhibits many frequen…
We examine transport properties of a magnetic superlattice with current perpendicular to the planes. In the limit that the phase-breaking and spin flip scattering lengths are greater than the system size, a multiple-scattering approach is used to calculate the 4-probe conductance. We show that by tuning the strength of tunnel barriers placed between the current and voltage probes giant magnetoresistance ratios of arbitrary strength and size are achievable.
