Some single-crystalline materials present an electrical resistivity which decreases between room temperature and low temperatures at zero magnetic field as in a good metal and switches to a nearly semiconductinglike behavior at low temperatures with the application of a magnetic field. Often, this is accompanied by a huge and nonsaturating linear magnetoresistance which remains difficult to explain. Here we present a systematic study of the magnetoresistance in single-crystal $γ$-PtBi$_2$. We observe that the angle between the magnetic field and the crystalline $c$ axis fundamentally changes the magnetoresistance, going from a saturating to a nonsaturating magnetic field dependence. In between, there is one specific angle where the magnetoresistance is perfectly linear with the magnetic field. We show that the linear dependence of the nonsaturating magnetoresistance is due to the formation of open orbits in the Fermi surface of $γ$-PtBi$_2$.
While pyrite-type PtBi2 with face-centered cubic structure has been predicted to be a three-dimensional (3D) Dirac semimetal, experimental study on its physical properties remains absent. Here we report the angular-dependent magnetoresistance (MR) measurements of PtBi2 single-crystal under high magnetic fields. We observed extreme large unsaturated magnetoresistance (XMR) up to 11.2 million percent at T = 1.8 K in a magnetic field of 33 T, which surpasses the previously reported Dirac materials, such as WTe2, LaSb and NbP. The crystals exhibit an ultrahigh mobility and significant Shubnikov-de…
The nonmagnetic compounds showing extremely large magnetoresistance are attracting a great deal of research interests due to their potential applications in the field of spintronics. PtBi$_2$ is one of such interesting compounds showing large linear magnetoresistance (MR) in its both the hexagonal and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) calculations to understand the mechanism of liner MR observed in the hexagonal PtBi$_2$. Our results uncover for the first time linear dispersive surface Dirac states at the $\ba…
Topological insulators are new kind of Dirac materials that possess bulk insulating and surface conducting behavior. They are basically known for their unique electronic properties at the surface. Here we present the magneto-transport properties of our high quality single crystalline Y(Lu)PtBi Heusler topological insulators, which belong to a group of noncentrosymmetric superconductor with Tc = 0:8 K. Both the compounds show semi-metallic behavior with low charge carrier of 6 x1018 cm^-3 for YPtBi and 8 x1019 cm^-3 for LuPtBi at 2 K. Magneto-conductivity measurements in the tilted field indica…
Large non-saturating magnetoresistance has been observed in various materials and electron-hole compensation has been regarded as one of the main mechanisms. Here we present a detailed study of the angle-dependent Shubnikov -de Haas effect on large magnetoresistance material pyrite-type PtBi$_{2}$, which allows us to experimentally reconstruct its Fermi-surface structure and extract the physical properties of each pocket. We find its Fermi surface contains four types of pockets in the Brillouin zone: three ellipsoid-like hole pockets $α$ with C$_4$ symmetry located on the edges (M points), one…
PtBi2 with a layered trigonal crystal structure was recently reported to exhibit an unconventional large linear magnetoresistance, while the mechanism involved is still elusive. Using high resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principle calculations, our experiment distinguishes the low-lying bulk bands from entangled surface states, allowing the estimation of the real stoichiometry of samples. We find significant electron doping in PtBi2, implying a substantial Bi …
We report large anisotropic magnetoresistance (AMR) behaviours in single lateral (Ga,Mn)As nanoconstriction of up to 1300%, along with large multistable telegraphic switching. The nanoconstriction devices are fabricated using high-resolution electron beam lithography of a 5 nm thick (Ga,Mn)As epilayer. The unusual behaviour exhibited by these devices is discussed in the context of existing theories for enhanced AMR ferromagnetic semiconductor nanoscale devices, particularly with regard to the dependence on the magnetotransport of the bulk material. We conclude that our results are most consist…
We present the magnetic field dependencies of transport properties for $R$PtBi ($R$ = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature and field dependent resistivity measurements of high quality $R$PtBi single crystals reveal an unusually large, non-saturating magnetoresistance (MR) up to 300 K under a moderate magnetic field of $H$ = 140 kOe. At 300 K, the large MR effect decreases as the rare-earth is traversed from Gd to Lu and the magnetic field dependence of MR shows a deviation from the conventional $H^{2}$ behavior. The Hall coefficient ($R_{H}$) for $R$ = Gd indicates a sign ch…
We investigate theoretically the spin-independent tunneling magnetoresistance effect in a graphene monolayer modulated by two parallel ferromagnets deposited on a dielectric layer. For the parallel magnetization configuration, Klein tunneling can be observed in the transmission spectrum, but at specific oblique incident angles. For the antiparallel magnetization configuration, the transmission can be blocked by the magnetic-electric barrier provided by the ferromagnets. Such a transmission discrepancy results in a tremendous magnetoresistance ratio and can be tuned by the inclusion of an elect…
Large magnetoresistive materials are of immense interest for a number of spintronic applications by developing high density magnetic memory devices, magnetic sensors and magnetic switches. Colossal magnetoresistance, for which resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external magnetic field, occurs mainly in phase separated oxide materials, namely manganites, due to the phase competition between the ferromagnetic metallic and the antiferromagnetic insulating regions. Can one further enhance the magnetoresistance by tuning the volume fraction of the two phases? In …
We report dynamical magnetotransport in a ferromagnetic metallic oxide, La0.7Sr0.3MnO3 using the ac impedance technique. The temperature dependence of the ac resistance(R) and the inductive reactance (X) of the complex impedance (Z = R+jX) under different dc bias magnetic fields (Hdc = 0-1 kOe) were studied for different frequencies f = 0.1 to 5 MHz of alternating current. The zero field R, which decreases smoothly around the Curie temperature TC for f = 100 kHz, transforms into a peak for f = 0.5-5 MHz. The peak decreases in amplitude, broadens and shifts downward in temperature as the bias f…
Tunneling magnetoresistance (TMR) via oxides or molecules includes fruitful physics, such as spin filtering and hybridized interface states, in addition to various practical applications using large TMR ratio at room temperature. Then, a larger TMR effect with a new fundamental physics is awaited because further progress on spintronics can be realized. Here we report a discovery of a gigantic TMR ratio of 1,400,000% in a C60-Co nanocomposite spin device. The observed effect is induced by a combination of a Coulomb blockade effect and a novel magnetic switching effect. Theoretical investigation…
Magnetic lanthanide half-Heuslers ($R$PtBi; $R$ being the lanthanide) represent an attractive subgroup of the Heusler family and have been identified as ideal candidates for time reversal symmetry breaking topological Weyl semimetals. In this paper, we present the detailed analysis of the magnetotransport properties of frustrated antiferromagnet TbPtBi. This material shows large, non-saturating magnetoresistance (MR) with unusual magnetic field dependence. The MR of TbPtBi is significantly anisotropic with respect to the magnetic field, applied along different crystallographic directions and i…
We show that extraordinary magnetoresistance (EMR) arises in systems consisting of two components; a semiconducting ring with a metallic inclusion embedded. The im- portant aspect of this discovery is that the system must have a quasi-two-dimensional character. Using the same materials and geometries for the samples as in experiments by Solin et al.[1;2], we show that such systems indeed exhibit a huge magnetoresistance. The magnetoresistance arises due to the switching of electrical current paths passing through the metallic inclusion. Diagrams illustrating the flow of the current density wit…
The compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, was recently reported by us to exhibit a sudden and huge enhancement in electrical resistivity (rho) at a critical magnetic field (H_cr) in the magnetically ordered state (<70 K) tracking isothermal magnetization (M) behavior. We have investigated the influence of external pressure (<15 kbar) and negative chemical pressure induced by Ge substitution for Si on M and rho as a function of temperature (5-300 K) and magnetic field (<120 kOe), with the primary aim of understanding the field-induced anomalies. Focussing on isothe…
We have investigated magnetic field dependence of the ac magnetoresitance and the magnetoreactance in La0.67Ba0.33MnO3 over a wide frequency range from f = 0 to 30 MHz. A huge ac magnetoresistance of 55 % at f = 15 MHz in a small magnetic field of H = 100 mT and magnetoreactance of 80 % at 2 MHz are reported. We show distinct field dependence of the magnetoreactance and the magnetoresistance with increasing frequency. It is shown that while the ac magnetoresistance is negative and shows a single peak at the origin for all frequencies except f = 30 MHz, the single peak in the magnetoreactance t…
Magnetotransport investigation of a half-Heusler antiferromagnet DyPdBi revealed hallmark features of Weyl semimetal: huge negative longitudinal magnetoresistance and planar Hall effect. Both effects have recently been linked to chiral magnetic anomaly - axial charge pumping between Weyl nodes. Magnetoresistance (MR) of single crystals of DyPdBi is very pronounced. In magnetic field longitudinal to electrical current direction it reaches -80% and its relative difference with respect to that measured in transverse field (expressed as anisotropic magnetoresistance) is extremely strong: -60% at 1…
The electrical conductance through a ring is sensitive to the threading magnetic flux. It contains a component that is periodic with an Aharonov-Bohm (AB) period equal to the quantum flux. In molecular/atomic loops on the nanometer scale, encircling very small areas, the AB period involves unrealistically huge magnetic fields. We show that despite this, moderate magnetic fields can have a strong impact on the conductance. By controlling the lifetime of the conduction electron through a pre-selected single state that is well separated from other states due to the quantum confinement effect, we …
Huge values of high field magnetoresistance have been recently reported in large arrays of CoFe nanoparticles embedded in an organic insulating lattice in the Coulomb blockade regime. An unusual exponential decrease of magnetoresistance with increasing voltage was observed, as well as a characteristic scaling of the magnetoresistance amplitude versus the field-temperature ratio. We propose a model which takes into account the influence of paramagnetic impurities on the transport properties of the system to describe these features. It is assumed that the non-colinearity between the core spins i…
We study the role of diamagnetic effects on the transport properties of metallic magnetic multilayers to elucidate whether they can explain the Giant Magnetoresistance (GMR) effect observed in those systems. Realistic Fermi surface topologies in layered ferromagnets are taken into account, with the possibilities of different types of orbits depending on the electron spin. Both configurations, with ferromagnetic and anti-ferromagnetic couplings between magnetic layers, are considered and the transmission coefficient for scattering at the interface boundary is modelled to include magnetic and ro…
Due to its two dimensional nature, ferromagnetism and charge doping can be induced by proximity and electric field effects in graphene. Taking advantage of these features, we propose an electrically engineered spin valve by combining two magnetic insulators (using EuO, EuS, or YIG) and three coating gates. Two top gates are used to cancel the heavy electron doping's in these magnets and one back gate is used to utilize the normal or half-metallic ferromagnetisms. We demonstrate that, when the second top gate is tuned to utilize the insulating or spin insulating states, huge giant magnetoresist…
We report observation of ferromagnetic (FM) ordering in organic semiconductors, namely regio-regular poly (3-hexyl thiophene) (RRP3HT) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM), in the temperature range of 5-300 K in addition to magnetoresistance (OMAR) observed in the diodes made from the same materials. Particle induced x-ray emission spectroscopy confirms the presence of dilute magnetic impurities in the materials mainly as residues from the synthesis process. However, upon blending these two materials with FM signal, the FM ordering is suppressed by a huge para…
We present electronic transport and magnetic properties of single crystals of semimetallic half-Heusler phase LuPdBi, having theoretically predicted band inversion requisite for nontrivial topological properties. The compound exhibits superconductivity below a critical temperature $T_{\rm c}=1.8\,$K, with a zero-temperature upper critical field $B_{\rm c2}\approx2.3\,$T. Although superconducting state is clearly reflected in the electrical resistivity and magnetic susceptibility data, no corresponding anomaly can be seen in the specific heat. Temperature dependence of the electrical resistivit…
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 th…
Thin films of Sm0.5Ca0.5MnO3 manganites with charge ordering (CO) properties and colossal magnetoresistance were synthesized by pulsed laser deposition technique on (100)-SrTiO3 and (100)-LaAlO3 substrates. We first compare the structural modifications as function of the substrate and film thickness. Secondly, measuring transport properties in magnetic fields up to 24T, we establish the temperature-field phase diagram describing the stability of the CO state and compare it to bulk material. We show that some structural modification induced by the substrate occurs and that the CO melting magnet…
Considerable progress has been recently made in the theoretical understanding of the colossal magnetoresistance (CMR) effect in manganites. The analysis of simple models with two competing states and a resistor network approximation to calculate conductances has confirmed that CMR effects can be theoretically reproduced using non-uniform clustered states. In this paper, the recently proposed Truncated Polynomial Expansion method (TPEM) for spin-fermion systems is tested using the double-exchange one-band, with finite Hund coupling $J_{\rm H}$, and two-band, with infinite $J_{\rm H}$, models. T…
Magnetoresistance (MR) is a characteristic that the resistance of a substance changes with the external magnetic field, reflecting various physical origins and microstructures of the substance. A large MR, namely a huge response to a low external field, has always been a useful functional feature in industrial technology and a core goal pursued by physicists and materials scientists. Conventional large MR materials are mainly manganites, whose colossal MR (CMR) can be as high as -90%. The dominant mechanism is attributed to spin configuration aligned by the external field, which reduces magnet…
RTX (R=rare earths, T= 3d/4d/5d, transition metals such as Sc, Ti, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and X=p-block elements such as Al, Ga, In, Si, Ge, Sn, As, Sb, Bi) series is a huge family of intermetallics compounds. These compounds crystallize in different crystal structures depending on the constituents. Though these compounds have been known for a long time, they came to limelight recently in view of the large magnetocaloric effect (MCE) and magnetoresistance (MR) shown by many of them. Most of these compounds crystallize in hexagonal and tetragonal crystal structures.…
In quasi-one-dimensional (quasi-1D) system, the charge density wave (CDW) transition temperature TCDW is usually lower than the mean-field-theory predicted TMF and a CDW fluctuation region exists between them. Here, we investigate the physical properties of PdTeI single crystal containing quasi-1D PdTe chains. Surprisingly, we find that the carrier concentration decreases gradually before the long-range CDW ordering state occurring at T1 ~ 110 K, reflecting the existence of strong CDW fluctuation with possible pseudogap state at T >> T1 because of dynamic charge separation of Pd ions (Pd3+ -> …
Single-phase multiferroic materials are usually considered useless because of the weak magnetoelectric effects, low operating temperature, and small electric polarization induced by magnetic orders. As a result, current studies on applications of the magnetoelectric effects are mainly focusing on multiferroic heterostructures and composites. Here we report a room-temperature giant effect in response to external magnetic fields in single-phase multiferroics. A low magnetic field of 1000 Oe applied on the spin-driven multiferroic hexaferrites BaSrCo2Fe11AlO22 and Ba0.9Sr1.1Co2Fe11AlO22 is able t…
We have investigated the effect of Ti doping on the transport properties coupled with the magnetic ones in Sm$_{0.55}$Sr$_{0.45}$Mn$_{1-η}$Ti$_η$O$_3$ ($0 \leq η\leq 0.04$). The parent compound, Sm$_{0.55}$Sr$_{0.45}$MnO$_3$, exhibits a first-order paramagnetic-insulator to ferromagnetic-metal transition just below $T_{\rm c}$ = 128 K. With substitution of Ti at Mn sites ($B$-site), $T_{\rm c}$ decreases approximately linearly at the rate of 22 K$\%^{-1}$ while the width of thermal hysteresis in magnetization and resistivity increases almost in an exponential fashion. The most spectacular effe…
We have investigated the Co-doping dependence of the structural, transport, and magnetic properties of ε-FeCoSi epilayers grown by molecular beam epitaxy on silicon (111) substrates. Low energy electron diffraction, atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy studies have confirmed the growth of phase-pure, defect-free ε-FeCoSi epitaxial films with a surface roughness of ~1 nm. These epilayers are strained due to lattice mismatch with the substrate, deforming the cubic B20 lattice so that it becomes rhombohedral. The temperature dependence o…
