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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Anisotropic magnetoresistance and nontrivial spin Hall magnetoresistance in Pt / α – F e 2 O 3 bilayers

Magnetic proximity effect has only been conclusively observed in ferromagnet-based systems. We report the observation of anomalous Hall effect and angular-dependent anisotropic magnetoresistance in Pt on antiferromagnetic Pt / α – F e 2 O 3 (0001) epitaxial films at 10 K, which provide evidence for the magnetic proximity effect. The Neel order of Pt / α – F e 2 O 3 and the induced magnetization in Pt show a unique angular-dependent magnetoresistance compared with all other ferromagnetic and antiferromagnetic systems. In conclusion, a macrospin response model is established and can explain the antiferromagnetic spin configuration and all main magnetoresistance features in the Pt / α – F e 2 O 3 bilayers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Intrinsic Mechanism for Anisotropic Magnetoresistance and Experimental Confirmation in Co{sub x}Fe{sub 1-x} Single-Crystal Fims.

Using first-principles transport calculations, we predict that the anisotropic magnetoresistance (AMR) of single-crystal CoxFe1-x alloys is strongly dependent on the current orientation and alloy concentration. An intrinsic mechanism for AMR is found to arise from the band crossing due to magnetization-dependent symmetry protection. These special k points can be shifted towards or away from the Fermi energy by varying the alloy composition and hence the exchange splitting, thus allowing AMR tunability. The prediction is confirmed by delicate transport measurements, which further reveal a reciprocal relationship of the longitudinal and transverse resistivities along different crystal axes.

Zeng, F. L.↗
DOE OSTI2020

Linear magnetoresistance with a universal energy scale in the strong-coupling superconductor Mo8Ga41 without quantum criticality

The recent discovery of a nonsaturating linear magnetoresistance in several correlated electron systems near a quantum critical point has revealed an interesting interplay between the linear magnetoresistance and the zero-field linear-in-temperature resistivity. These studies suggest a possible role of quantum criticality on the observed linear magnetoresistance. Here we report our discovery of a nonsaturating, linear magnetoresistance in Mo 8 Ga 41 , a nearly isotropic strong electron-phonon coupling superconductor with a linear-in-temperature resistivity from the transition temperature to ~ 55 K. The growth of the resistivity in field is comparable to that in temperature, provided that both quantities are measured in the energy unit. Overall, our data sets are remarkably similar to magnetoresistance data of the optimally doped La 2 - x Sr x CuO 4 , despite the clearly different crystal and electronic structures, and the apparent absence of quantum critical physics in Mo 8 Ga 41 . A new empirical scaling formula is developed, which is able to capture the key features of the low-temperature magnetoresistance data of Mo 8 Ga 41 , as well as the data of La 2 - x Sr x CuO 4 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Evidence for Interfacial Octahedral Coupling as a Route to Enhance Magnetoresistance in Perovskite Oxide Superlattices

Engineering octahedral rotations in oxide heterostructures is a promising route for controlling magnetic properties in perovskites, with recent work focusing on magnetic-ordering temperatures and magnetic anisotropies. Here the effects of interfacial octahedral coupling on magnetoresistance are demonstrated in a series of (La 0.7 Sr 0.3 MnO 3 ) n /(LaFeO 3 ) 10 superlattices grown on (001)- and (111)-oriented SrTiO 3 substrates. The different crystallographic orientations allow for the interfacial octahedral connectivity to be tuned, with weaker interfacial coupling present at the (001)-oriented than the (111)-oriented structures as revealed by density functional theory calculations. In n = 14 superlattices, the effect of orientation on the physical properties is minimal with both (001)- and (111)-oriented samples exhibiting similar magnetoresistance. As the fraction of interfacial volume within the LSMO layers is increased by decreasing n, the magnetoresistive behavior of the samples diverges with significantly larger magnetoresistance magnitudes present in the (111)-oriented superlattices. Furthermore, the results are consistent with octahedral coupling playing a greater role in the functional properties at (111)-heterointerfaces and demonstrate a structure-driven approach to tuning interfacial magnetoresistance in complex-oxide heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Possible scale invariant linear magnetoresistance in pyrochlore iridates Bi 2 Ir 2 O 7

We report the observation of a linear magnetoresistance in single crystals and epitaxial thin films of the pyrochlore iridate Bi 2 Ir 2 O 7 . The linear magnetoresistance is positive and isotropic at low temperatures, without any sign of saturation up to 35 T. As temperature increases, the linear field dependence gradually evolves to a quadratic field dependence. The temperature and field dependence of magnetoresistance of Bi 2 Ir 2 O 7 bears strikingly resemblance to the scale invariant magnetoresistance observed in the strange metal phase in high Tc cuprates. However, the residual resistivity of Bi 2 Ir 2 O 7 is more than two orders of magnitude higher than the curpates. Our results suggest that the correlation between linear magnetoresistance and quantum fluctuations may exist beyond high temperature superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Rashba spin-orbit coupling enhanced magnetoresistance in junctions with one ferromagnet

We explain how Rashba spin-orbit coupling (SOC) in a two-dimensional electron gas (2DEG), or in a conventional s-wave superconductor, can lead to a large magnetoresistance even with one ferromagnet. However, such enhanced magnetoresistance is not generic and can be nonmonotonic and change its sign with Rashba SOC. For an in-plane rotation of magnetization, it is typically negligibly small for a 2DEG and depends on the perfect transmission which emerges from a spin-parity-time symmetry of the scattering states, while this symmetry is generally absent from the Hamiltonian of the system. The key difference from considering the normal-state magnetoresistance is the presence of the spin-dependent Andreev reflection at superconducting interfaces. In the fabricated junctions of quasi-2D van der Waals ferromagnets with conventional s-wave superconductors (Fe 0.29 ⁢TaS 2 /NbN) we find another example of enhanced magnetoresistance where the presence of Rashba SOC reduces the effective interfacial strength and is responsible for an equal-spin Andreev reflection. The observed nonmonotonic trend in the out-of-plane magnetoresistance with the interfacial barrier is an evidence for the proximity-induced equal-spin-triplet superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Temperature scaling behavior of the linear magnetoresistance observed in high-temperature superconductors

An analytical model invoking variations in the charge-carrier density is used to generate magnetoresistance curves that are almost indistinguishable from those produced by sophisticated numerical models. This demonstrates that, though disorder is pivotal in causing linear magnetoresistance, the form of the magnetoresistance thus generated is insensitive to details of the disorder. Additionally, taken in conjunction with the temperature (T) dependence of the zero-field resistivity, realistic levels of disorder are shown to be sufficient to explain the linear magnetoresistance and field-T resistance scaling observed in high-temperature pnictide and cuprate superconductors. Hence, though the T-linear zero-field resistance is a definite signature of the “strange metal” state of high-temperature superconductors, their linear magnetoresistance and its scaling is unlikely to be so.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Temperature-Dependent Magnetoresistance of Single-Layer Graphene

The magnetoresistances of single-layer graphene samples with various types of scattering impurities are measured over wide temperature and magnetic field ranges. The magnetoresistance of samples with a short-range potential is shown to be proportional to the square root of the magnetic field except for the cases of relatively low concentrations, where the magnetoresistance is linear. The square-root temperature dependence of the magnetoresistance is analyzed and good agreement with theoretical calculations is obtained. These results indicate that the square-root magnetoresistance in low magnetic fields can be considered as a characteristic feature of single-layer graphene with a short-range disorder.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Large-field magnetoresistance of nanometer scale nickel films grown on molybdenum disulfide

The magnetoresistance of thin nickel films grown on molybdenum disulfide was measured in perpendicular magnetic fields as high as 90 kOe. Films with thicknesses of 20 nm provided continuous surfaces for measurement. The magnetoresistance was found to be linear with respect to the applied magnetic field with no sign of saturation. There was also no evidence of hysteresis or temperature dependence between 100 to 300 K. STM measurement showed the deposited Ni forms a continuous film of extremely small nanoclusters. However, the field dependence of magnetoresistance was found to be significantly larger than bulk Ni, which is in turn larger than Ni with nanoscale grains. We expect the unusual magnetoresistance behavior to arise from some property of the Ni-MoS 2 interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Valley-contrasting orbital magnetic moment induced negative magnetoresistance

The valley-contrasting orbital magnetic moment of Bloch electrons allows the lifting of valley degeneracy by an out-of-plane magnetic field. We demonstrate that this leads to negative magnetoresistance, utilizing a gapped two-dimensional multivalley model as an example. An intuitive physical picture in terms of the increased carrier density from a magnetic gating effect is proposed for this negative magnetoresistance. In particular, giant negative magnetoresistance is achieved after one of the two valleys is depleted by the magnetic field. Furthermore, this mechanism of negative magnetoresistance is argued to be relevant in ionic-liquid gated gapped graphene with a small effective mass.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetization-governed magnetoresistance anisotropy in the topological semimetal CeBi

Magnetic topological semimetals, the latest member of topological quantum materials are attracting extensive attention as they may lead to topologically-driven spintronics. Currently, magnetotransport investigations on these materials are focused on the anomalous Hall effect. Here,we report on the magnetoresistance anisotropy of topological semimetal CeBi, which has tunable magnetic structures arising from localized Ce 4 f electronsandexhibits both negative and positive magnetoresistances, depending on the temperature. We found that the angle dependence of the negative magnetoresistance, regardless of its large variation with the magnitude of the magnetic field and with temperature, is solely dictated by the field-induced magnetization that is orientated along a primary crystalline axis and flops under the influence of a rotating magnetic field.The results reveal the strong interaction between conduction electronsand magnetization in CeBi. They also indicate that magnetoresistance anisotropy can be used to uncover the magnetic behavior and the correlation between transport phenomena and magnetism in magnetic topological semimetals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magnetoresistance effects in cadmium arsenide thin films

In-plane magnetoresistance effects in the three-dimensional Dirac semimetal cadmium arsenide are studied as a function of film growth orientation, film thickness and surface Fermi level. For films with the Fermi level near the bulk nodes, which are gapped for very thin films, a pronounced planar Hall effect is observed due to the combination of magnetoresistance effects from the Berry phase and orbital magnetoresistance. At high Fermi levels, surface state transport produces weaker magnetoresistance effects. Furthermore, the results are discussed in the context of detecting signatures of the chiral anomaly.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Crossover behavior in the magnetoresistance of thin flakes of the topological material ZrTe 5

ZrTe 5 is a layered material that exhibits intricate topological effects. Intensive theoretically and experimental efforts have been devoted to try to understand the physics in this materials. In this paper the temperature dependent magneto-transport properties of ZrTe 5 thin flakes are investigated. A characteristic temperature T* is observed in the temperature dependence of three different types of magnetoresistance simultaneously, which are the saturated Hall anomaly, the chiral anomaly and the longitudinal magnetoresistance. Furthermore, the value of T* decreases monotonically from 200K to 160K with increasing thickness of the ZrTe 5 thin flakes from 42nm to 89nm. Temperature induced topological phase transitions are attributed to the cause of such anomaly in the three types of magnetoresistance at T*. Overall, our findings provide a multi-parameter indicator for the emergence of topological phase transition in ZrTe 5 and could be extended to the study of other topological materials. The temperature dependence of the three types of magnetoresistance also shed light on the role of anomalous Hall Effect in the transport properties of ZrTe 5 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Giant Anisotropic Magnetoresistance due to Purely Orbital Rearrangement in the Quadrupolar Heavy Fermion Superconductor PrV 2 Al 20

In this report, we discuss 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 and 25 T, accompanied by a large jump at 12 T in the magnetoresistance (ΔMR ~ 100%) and in the anisotropic magnetoresistivity ratio by ~20%. These observations suggest that the strong hybridization between the conduction electrons and anisotropic quadrupole moments leads to the Fermi surface reconstruction upon crossing the field-induced antiferroquadrupole (orbital) rearrangement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Relationship between magnetoresistance behavior and magnetic states in intercalated compounds Fe x TiS 2

Here, temperature and field-dependent neutron powder diffraction (NPD) measurements have been performed to reveal the nature of the unusual evolution of the magnetoresistance behavior with increasing Fe content in the intercalated compounds Fe x TiS 2 (with x=0.25,0.33,0.50,0.55) synthesized by solid-phase reaction method with prolonged homogenization heat treatment. As derived from neutron diffraction measurements, both the Fe 0.25 TiS 2 and the Fe 0.50 TiS 2 compound exhibit an antiferromagnetic (AFM) order below their respective Néel temperatures T N ≈52 K and T N ≈140K, which results in the presence of a large magnetoresistance accompanying the field-induced phase transition from AFM to the ferromagnetic (FM) state. At low temperatures, this AFM-FM transition is irreversible, confirmed by the irreversibility of changes in the NPD patterns and the presence of remnant magnetoresistance. In contrast, Fe 0.33 TiS 2 shows short-range magnetic order at T f ≈44 K due to a triangular network of intercalated Fe atoms and frustrations of exchange interactions with a field-induced FM alignment of Fe magnetic moments in an applied magnetic field as revealed by NPD measurements. The field-induced transformations of the cluster glass magnetic state in this compound lead to a significant decrease in electrical resistivity. According to NPD data, a reduced impact of an external magnetic field on the electrical resistivity of the compound Fe 0.55 TiS 2 can be ascribed to the presence of ferromagnetic or ferrimagnetic order in compounds with the Fe concentrations above x=0.50. The results obtained indicate that the distribution of the Fe atoms, along with their concentration in Fe x TiS 2 layered compounds, plays a decisive role in the formation of the magnetic state and the behavior of the magnetoresistance.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Extreme Transverse Magnetoresistance in TiZn 16

Extreme magnetoresistance (XMR) is a phenomenon characterized by an increase in resistance by factors of 10 4 –10 7 % when a magnetic field is applied. This phenomenon is found in a number of semimetals such as WTe 2 , PtSn 4 , Cd 3 As 2 , and LaSb. The origin of XMR is still hotly debated, possibly with different materials having different (or multiple) explanations. Extreme transverse magnetoresistance of up to 8000% at 14 T and 1.8 K is measured in TiZn 16 , a semimetal with a multitude of bands crossing the Fermi energy, akin to PtSn 4 . The magnetoresistance is suppressed when the magnetic field is rotated to be parallel to the applied current, similar to PtSn 4 and PdSn 4 . The resistance of TiZn 16 follows Kohler's rule, but displays different behavior under an applied transverse field and under a longitudinal magnetic field, suggesting distinct electrical phases. Also present are Shubnikov-de Haas and de Haas-van Alphen oscillations with a transverse magnetic field up to 43 T, showing that despite an insulator-like temperature-resistance curve, charge carriers are still present. This positions TiZn 16 as an interesting addition to the investigation of XMR materials as a multi-band metal with complex Fermi surface geometries.

extreme magnetoresistance↗
DOE OSTI2021

Large Magnetoresistance in Scandium Nitride Magnetic Tunnel Junctions Using First Principles

Abstract The state‐of‐the‐art magnetic tunnel junction, a cornerstone of spintronic devices and circuits, uses a magnesium oxide tunnel barrier that provides a uniquely large tunnel magnetoresistance at room temperature. However, the wide bandgap and band alignment of magnesium oxide‐iron systems increases the resistance‐area product and creates variability and breakdown challenges. Here, the authors study using first principles narrower‐bandgap scandium nitride (ScN) transport properties in magnetoresistive junctions in comparison to magnesium oxide. The results show a high magnetoresistance in Fe/ScN/Fe via Δ 1 and symmetry filtering with low wave function decay rates, suggesting scandium nitride could be a new barrier material for spintronic devices.

Karki, Suyogya↗