Magnitude Of Magnetoresistance Research Articles

Current orientation dependence of anisotropic magnetoresistance in SmCo[formula omitted]

Anisotropic magnetoresistance in a highly oriented SmCo5 device was systematically investigated at various temperatures. Currents were applied along the magnetic easy axis and the magnetic hard axis of SmCo5, and the corresponding anisotropic magnetoresistances were measublack, respectively. In both these instances, the anisotropic magnetoresistances exponentially decrease as the temperature increases. Notably, the anisotropic magnetoresistance magnitudes for the two instances intersect at 220 K. This intersection may relate to the compensation between the spin and orbital magnetic moments of Sm, which is also considered to be a hint of a ferromagnetic and ferrimagnetic transition in SmCo5. The results exhibit the capability to monitor magnetic configurations through magnetotransport properties, potentially facilitating the development of spintronic devices based on SmCo5.

Nonvolatile Electric Control of Antiferromagnet CrSBr.

van der Waals magnets are emerging as a promising material platform for electric field control of magnetism, offering a pathway toward the elimination of external magnetic fields from spintronic devices. A further step is the integration of such magnets with electrical gating components that would enable nonvolatile control of magnetic states. However, this approach remains unexplored for antiferromagnets, despite their growing significance in spintronics. Here, we demonstrate nonvolatile electric field control of magnetoelectric characteristics in van der Waals antiferromagnet CrSBr. We integrate a CrSBr channel in a flash-memory architecture featuring charge trapping graphene multilayers. The electrical gate operation triggers a nonvolatile 200% change in the antiferromagnetic state of CrSBr resistance by manipulating electron accumulation/depletion. Moreover, the nonvolatile gate modulates the metamagnetic transition field of CrSBr and the magnitude of magnetoresistance. Our findings highlight the potential of manipulating magnetic properties of antiferromagnetic semiconductors in a nonvolatile way.

Spin-related negative magnetoresistance in germanium films

Herein, we report the transport properties of Ge films. The variable-range hopping transport at low temperatures (T≲50K) and thermal activation transport at high temperatures (T≳50K) are observed in our Ge films. In the different temperature regimes, the anomalous magnetotransport properties are observed. In the low-temperature regime (T≲15K), the negative magnetoresistance (MR) at low field and positive MR at high field can be seen. In the moderate-temperature regime (15K≲T≲100K), the positive MR curve gradually evolves from a linear curve to a parabolic curve with increasing temperature, and the MR magnitude appears to be insensitive to temperature. In the high-temperature regime (T≳100K), the positive MR value increases with increasing temperature. By considering the angular-dependent MR, we can determine that the negative MR comes from the spin-related mechanism, and the positive MR is caused by the orbital-related mechanism. However, further study is required to determine the exact mechanisms behind the anomalous magnetotransport properties.

Comparing Electrical Magnetochiral Anisotropy and Chirality-Induced Spin Selectivity.

The combination of chirality and magnetism has steadily grown over the past decennia into an area of intense research that evolves around two distinct manifestations and in two nonoverlapping communities: electrical magnetochiral anisotropy (eMChA) and chirality-induced spin-selectivity (CISS). Here, we discuss the similarities and differences of these two effects. Whereas the original CISS reports suggest an intimate relation with eMChA, magnetoresistance (MR) results on two-terminal chiral devices attributed to CISS have symmetry properties that are different from those of eMChA. At the same time, the magnitudes of CISS MR and eMChA turn out to be similar when normalized to current density and spin polarization, suggesting a common underlying mechanism.

Effect of deposition potential and saccharin addition on structural, magnetic and magnetoresistance characteristics of NiCoFeCu films

Abstract NiCoFeCu films were electrodeposited on Ti substrates at different deposition potentials and different concentrations of saccharin added to solution. Compositional analysis showed that although Ni was the highest concentration in solution at low potentials of −1.0 V and −1.5 V, the Ni content was lower than the Co content in the films. Anomalous co-deposition behaviour of iron group metals was observed. When the deposition potential increased to −2.0 V and −2.5 V, the Ni content of films increased while the Co, Fe and Cu content decreased. In the case of saccharin addition to the solution, there is a slight change in the film content. All films have face-centred cubic structure. Structural analysis clearly showed that the potential has a significant effect on the texture degree of the films, since the crystal texture changed from (111) to (220) with increasing potential. The surface morphology of the films was observed to be affected by the deposition potential and saccharin concentration. For the magnetic analysis, saturation magnetisation, M s value gradually decreased from 905 to 715 emu/cm3 with the variation of film content caused by the increase of the potential from −1.0 V to −2.5 V. And, a slight increase in M s was detected with the addition of saccharin. Besides, the longitudinal and transverse magnetoresistance magnitudes increased from ∼2.5 % to 7.0 % with increasing deposition potential and all films exhibit anisotropic magnetoresistance. Films with desired magnetic properties can be obtained for potential use as magnetic materials in electronics such as magnetoresistive devices.

Large 3D anisotropy of magnetoresistance in MoAlB

Materials with large three-dimensional (3D) anisotropic magnetoresistance (MR) have very important applications in anisotropic magnetoresistance sensors and magnetometers. Herein, we have observed a large 3D anisotropy of MR in nonmagnetic MoAlB single crystal. Specially, the MR ratio (MRa: MRb: MRc) reaches up to 140.5 : 1: 22, when electric current is along a-/b-/c-axis with an applied magnetic field of 8.5 T at 5 K. To clarify the origins of 3D anisotropic MR, angular MR and direction-dependent Hall coefficient measurements as well as first-principles calculations were performed. The nearly electron-hole compensation and the mixed d-p orbital texture are the important origins of the MR effect along a-/c-axis, and the anisotropy of MR originates from the anisotropic Fermi surface and carrier scattering along a-/c-axis in MoAlB. Whereas, the open orbit is a dominant origin along b-axis of MoAlB. Furthermore, the factors affecting the magnitude of MR are given by using two-band model, and possible control strategies are proposed. This work not only proposes a new idea for exploring single-phase nonmagnetic 3D anisotropic MR material, but also provides a key material for the design and development of new 3D anisotropic magnetoresistance sensors and magnetometers in the future.

Transport properties of As-F-based molecular magnetic tunnel junctions

By combining the density functional theory with non-equilibrium Green's function method, we theoretically design and investigate the spin-dependent transport properties of two molecular magnetic tunnel junctions (MMTJs) with the AsFNRs embedded in zigzag graphene nanoribbons in parallel and antiparallel spin configurations. The findings reveal that the MMTJs have distinct transport characteristics depending upon the orientations of the AsFNRs. Changing the spin configurations leads to two different net spin currents, and the maximal order of the tunneling magnetoresistance magnitude can reach 107%. In addition, a negative differential resistance (NDR) effect is found in our MMTJs. Our findings provide suitable candidates of MMTJs for the future spintronic devices.

Spin transport in fully ferromagnetic p–n junctions

We systematically investigate the spin-dependent transport properties of fully ferromagnetic (Ga,Fe)Sb/GaSb/(In,Fe)Sb and (Ga,Fe)Sb/(In,Fe)As p–n junctions grown by low-temperature molecular beam epitaxy. The (Ga,Fe)Sb/GaSb/(In,Fe)Sb p–n junctions show high Curie temperature (170–310 K) and rectifying characteristics. The polarity and magnitude of magnetoresistance of the (Ga,Fe)Sb/GaSb/(In,Fe)Sb junctions strongly depend on the GaSb spacer thickness (t). Large positive magnetoresistance (MR, 58%) and negative MR (−1.6%) were observed at 3.7 K for the samples with t = 2 and 4 nm, respectively. When the n-type (In,Fe)Sb layer was replaced by the n-type (In,Fe)As, giant MR over 500% was observed, which can be explained by spin-valve and spin-splitting effects. Our results shed light on rich spin-transport physics observed in fully ferromagnetic p–n junctions.

Magnetoresistance effect realized in current-in-plane Van der Waals spin valve structure by electrically switchable magnetization

We present a device concept for magnetoresistance (MR) effect in which two Van der Waals (vdW) spin valves are used as the left and right ferromagnetic (FM) leads connected by a bilayer graphene as the channel material of the central scattering region. Unlike conventional current-perpendicular-to-plane magnetic tunnel junction consisting of two FM thin films with a thin insulating barrier sandwiched between them, the FM leads in our proposed current-in-plane MR device are vdW spin valves. This is important because the application of an out-of-plane electric field allows control of the direction and magnitude of the magnetization in vdW spin valves. Moreover, we show that the oscillatory behavior is found in the MR and conductance as the height (depth) of the barrier (well) of the scattering region with the p(n)-doping increase, or the width of the scattering region increase. Remarkably, when the potential barrier is present, the oscillation magnitude of MR is considerable and can be changed from positive to negative value, whereas for the potential well, the oscillation amplitude is relatively small and is always positive. Therefore, we hope that this device configuration with electrically tunable large MR can open up new possibilities for future lower power magneto-electric devices since no current-induced magnetization switching.

Spin-flip-driven giant magnetotransport in A-type antiferromagnet NaCrTe2

The value of angle-dependent magnetoresistance (MR) synergistically and simultaneously depends on the magnitudes of magnetoresistance (MR) and magnetocrystalline anisotropy energy (MAE). In a magnetic material, the concurrence of gigantic angle-dependent MR and MR signals is rather difficult due to weak spin-lattice coupling and small MAE. Here we report the considerable magnetotransport effect in layered A-type antiferromagnetic (AFM) $\mathrm{NaCr}{\mathrm{Te}}_{2}$ by realigning the spin configurations. Above 3 (8) T, the antiparallel spins of adjacent layers experience a spin-flip transition to a parallel alignment along the $c$ axis ($ab$ plane). Theoretical calculations reveal that the energy band gap narrows from 0.39 to 0.11 eV, accompanying a transition from semiconductor (high-$R$ state) and half semiconductor (low-$R$ state), respectively. Thus, a gigantic negative MR ratio of \ensuremath{-}90% is obtained at 10 K. More importantly, the decrement of $R$ along $H\ensuremath{\parallel}c$ is far quicker than that of $H\ensuremath{\parallel}ab$ because the MAE of the Ising-like ferromagnetic (FM) state is $1017\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{eV}/{\mathrm{Cr}}^{3+}$ lower than that of XY-like FM. The distinct trends result in the angle-dependent MR ratio of 732% at 10 K. These findings unravel the intrinsic origin of magnetoresistance in $\mathrm{NaCr}{\mathrm{Te}}_{2}$ and will stimulate us to explore the $H$-sensitive transport property in more AFM materials.

Vertical WS2 spin valve with Ohmic property based on Fe3GeTe2 electrodes* *Project supported by the National Key R&D Program of China (Grant No. 2017YFA0303400), the National Natural Science Foundation of China (Grant No. 61774144), Beijing Natural Science Foundation Key Program (Grant No. Z190007), and Chinese Academy of Sciences (Grant Nos. QYZDY-SSW-JSC020, XDB44000000, and XDB28000000).

The two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been recently proposed as a promising class of materials for spintronic applications. Here, we report on the all-2D van der Waals (vdW) heterostructure spin valve device comprising of an exfoliated ultra-thin WS2 semiconductor acting as the spacer layer and two exfoliated ferromagnetic Fe3GeTe2 (FGT) metals acting as ferromagnetic electrodes. The metallic interface rather than Schottky barrier is formed despite the semiconducting nature of WS2, which could be originated from the strong interface hybridization. The spin valve effect persists up to the Curie temperature of FGT. Moreover, our metallic spin valve devices exhibit robust spin valve effect where the magnetoresistance magnitude does not vary with the applied bias in the measured range up to 50 μA due to the Ohmic property, which is a highly desirable feature for practical application that requires stable device performance. Our work reveals that WS2-based all-2D magnetic vdW heterostructure, facilitated by combining 2D magnets, is expected to be an attractive candidate for the TMDCs-based spintronic applications.

Temperature-Dependent Magnetoresistance in Polycrystalline Ni81Fe19 Thin Film on Si (100)

Magnetoresistance (MR) in thin films stems from different types of scattering mechanism present in the film. We report a systematic study of the temperature-dependent magnetoresistance behaviour in the pulsed DC magnetron sputtered Ni81Fe19 thin film on Si (100). X-ray diffraction study reveals the polycrystalline nature of the film along with the presence of preferred orientation. X-ray reflectivity measurement shows very low interface roughness (0.55 ± 0.04 nm). Temperature-dependent resistivity measurement is performed over a temperature range of 25–300 K, unveiling the dominance of electron-magnon scattering and impurity scattering at lower temperature (25–250 K) and electron-phonon scattering at higher temperature (above 250 K). In the investigated temperature range (30–300 K), the MR magnitude is found to reduce from 0.97 to 0.51% with increment in measurement temperature from 30 to 300 K. This reduction is attributed to the enhancement in phonon scattering at higher temperatures, and relatively suppressed ordering influence of magnetic field at higher temperature due to higher thermal activation energy and impurity scattering.

Anomalous linear magnetoresistance in high-quality crystalline lead thin films

Intriguing novel phenomena in lead films inspire new understanding of quantum physics, such as quantum size effect and quantum phase transitions etc. The improvement of the sample quality makes it even more promising to explore the intrinsic properties in two-dimensional system. In this paper, we show that the crystalline interfacial striped incommensurate layer can increase the quality of the lead films and significantly enhance the magnitude of magnetoresistance. By performing systematic transport measurement, a predominant anomalous linear magnetoresistance is revealed, and the widely used Parish-Littlewood model and Abrikosov's explanation fail to describe the observation. Instead, we propose a new model of linear magnetoresistance based on linear band structure, which shows a good agreement with the experimental results. Our studies reveal a novel origin of linear magnetoresistance which may also be helpful to understand the linear magnetoresistance in other materials with linear dispersion of electronic structure.

The influence of Cu spacer morphology in Cu/Py/Cu/Co/IrMn spin valves with induced non-collinear spin structures

Non-collinear exchange couplings between Py and Co layers (0°⩽φ⩽90°) were achieved in Py(10)/Cu(5)/Co(10)/IrMn(8) (thickness values in nm) spin valves by modifying their layer morphologies using oblique deposition in a confocal sputtering setup. Two series of spin valves were prepared by keeping the sample holder fix during the depositions, except for the Cu spacers that were deposited using either fixing (Series-I) or spinning mode (Series-II). Series-I (Series-II) has Cu spacer layers composed by oriented (non-oriented) grains and Cu/Co interfacial roughnesses relatively rougher (smoother), favoring lower (higher) interlayer exchange couplings and exchange bias fields. The magnetization easy axis of Py and the unidirectional anisotropy axis followed the expected directions, while the Co uniaxial axis is surprisingly dephased by (15±5)° for 0°⩽φ<90°. The angular offset between the Co uniaxial axis and the Py uniaxial (unidirecional anisotropy) axis was more pronounced in Series-I, indicating that the Cu spacer roughness played an important role in the interlayer exchange couplings and also in the Co spin reorientation effect. The magnetoresistance magnitudes were similar to those found in the literature for ordinary Py/Cu/Co multilayers. However, it reduces as the φ-angle increased, an effect associated with the enhancement of the interface roughness due to the misalignment of the oriented grains of adjacent layers.

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

AbstractEngineering 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 (La0.7Sr0.3MnO3)n/(LaFeO3)10 superlattices grown on (001)‐ and (111)‐oriented SrTiO3 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. 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.

Anomalous Non-Linear to Linear Shift in Magnetoresistance of Amorphous Carbon Films

Non-linear to linear negative magnetoresistance (MR) was studied under the magnetic field ranging from −7 T to 7 T with a change in measurement temperature from 2 K to 300 K. Under the magnetic field of 7 T, a maximum MR magnitude of 8.2% was observed at 2 K. The chemical vapor deposition technique was adopted to synthesize the amorphous carbon thin films. Non-saturated and non-linear negative MR was observed for the lower temperatures, while 10 K was observed as transition temperature. Afterwards, the more likely linear MR behavior was observed up to 300 K. MR shape change was correlated with the structural morphology of metallic disordered graphitic layers or the random stacking of graphene layers with amorphous carbon. The negative MR mechanism for such a non-linear to linear shift was partially assumed as a combined effect of the diffused scattering theory and the weak localization theory. The negative MR effect has a direct relation with the degree of structural order.

Nonvolatile Control of the Electronic Properties of In2-xCrxO3 Semiconductor Films by Ferroelectric Polarization Charge.

A series of Cr-doped In2-xCrxO3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 104% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In2O3-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

Superior Magnetoresistance Performance of Hybrid Graphene Foam/Metal Sulfide Nanocrystal Devices.

Interfaces between metals and semiconducting materials can inevitably influence the magnetotransport properties, which are crucial for technological applications ranging from magnetic sensing to storage devices. By taking advantage of this, a metallic graphene foam is integrated with semiconducting copper-based metal sulfide nanocrystals, i.e., Cu2ZnSnS4 (copper-zinc-tin-sulfur) without direct chemical bonding and structural damage, which creates numerous nanoboundaries that can be basically used to tune the magnetotransport properties. Herein, the magnetoresistance of a graphene foam is enhanced from nearly 90 to 130% at room temperature and under the application of 5 T magnetic field strength due to the addition of Cu2ZnSnS4 nanocrystals in high densities. We believe that the enhancement of magnetoresistance in hybrid graphene foam/Cu2ZnSnS4 nanocrystals is due to the evolution of the mobility fluctuation mechanism, triggered by the formation of nanoboundaries. Incorporating Cu2ZnSnS4 nanocrystals into a graphene foam not only provides an effective way to further enhance the magnitude of magnetoresistance but also opens a suitable window to achieve efficient and highly functional magnetic sensors with a large, linear, and controllable response.

Structural and Magnetoresistance Properties of Transfer-Free Amorphous Carbon Thin Films

The control of the morphologies and thus the optical, electrical, and magnetic effect of 2D thin films is a challenging task for the development of cost-efficient devices. In particular, the angular dependent magnetoresistance (MR) of surface thin films up to room temperature is an interesting phenomenon in materials science. Here, we report amorphous carbon thin films fabricated through chemical vapor deposition at a SiO2 substrate. Their structural and angular magnetoresistance properties were investigated by several analytical tools. Specifically, we used a physical property measurement system to estimate the magnitude of the angular MR of these as-prepared sample thin films from 2 K to 300 K. An angular MR magnitude of 1.6% for the undoped a-carbon thin films was found up to 300 K. Under the magnetic field of 7 T, these films possessed an angular MR of 15% at a low temperature of 2 K. A high disorder degree leads to a large magnitude of MR. The grain boundary scattering model was used to interpret the mechanism of this angular MR.

Colossal magnetoresistance in low-doped EuTi1−xNbxO3 (x = 0.003 and 0.005)

We studied the magnetization (M), magnetostriction (λ||), resistivity (ρ), magnetoresistance (MR), and thermoelectric properties of low-doped EuTi1−xNbxO3 (x = 0.003 and 0.005). In both the samples, Eu2+(4f7) spins order antiferromagnetically at TN≅5.5K, and the paramagnetic to antiferromagnetic transition is accompanied by a spontaneous contraction of the length in the absence of magnetic field and a positive magnetostriction under external magnetic fields. ρ(T) shows non-metallic behavior in the temperature range 400–2.5 K but a weak kink at TN in a zero magnetic field. The application of an external magnetic field induces the semimetal-metal transition and negative MR. The magnitude of negative MR has a maximum value of 82% (57%) under 7 T for x = 0.003 (0.005) at T = 2.5 K, and the MR monotonously decreases with increasing temperature. Thermopower data indicate that the doped carriers are electrons. It is suggested that scattering of 4d1 electrons doped in the impurity band by 4f spin fluctuations is responsible for the colossal magnetoresistance.