Measurements Of Angular Dependence Research Articles

In-plane anisotropic magnetoresistance and planar Hall effect in off-stoichiometric single crystal Mn3Ga

We report the observation of in-plane anisotropic magnetoresistance (AMR) and planar Hall effect in our recently discovered kagome antiferromagnetic off-stoichiometric single crystal of Mn3Ga. We found that the in-plane AMR is dominated by a sixfold symmetry at low temperature due to the kagome lattice magnetocrystalline anisotropy. However, an unusual fourfold symmetry is also revealed by the angular-dependent AMR measurements, which originates from the little distortion of the crystal accompanying the slight ferromagnetic transition. Moreover, we also found a clear planar Hall effect signal in off-stoichiometric single crystal of Mn3Ga, which may be related to the chiral anomaly, one of the signatures of the magnetic Weyl fermions.

Magnetotransport properties of ternary tetradymite films with high mobility

(Bi,Sb)2(Te,Se)3 tetradymite materials are among the most efficient for thermoelectric energy conversion, and most robust for topological insulator spintronic technologies, but should possess rather disparate doping properties to be useful for either technology. In this work, we report results on the molecular beam epitaxy growth of p-type (Bi0.43Sb0.57)2Te3 and n-type Bi2(Te0.95Se0.05)3 that can contribute to both technology bases, but are especially useful for topological insulators where low bulk doping is critical for devices to leverage the Dirac-like topological surface states. Comprehensive temperature, field and angular dependent magnetotransport measurements have attested to the superior quality of these ternary tetradymite films, displaying low carrier density on the order of 1018 cm−3 and a record high mobility exceeding 104 cm2 V−1 s−1 at 2 K. The remarkable manifestation of strong Shubnikov–de Haas (SdH) quantum oscillation under 9 T at liquid helium temperatures, as well as the analyses therein, has allowed direct experimental investigation of the tetradymite electronic structure with optimized ternary alloying ratio. Our effort substantiates tetradymites as a critical platform for miniaturized thermoelectric cooling and power generation in wearable consumer electronics, as well as for futuristic topological spintronics with unprecedented magnetoelectric functionalities.

Epitaxial Fe/Rh bilayers for efficient spin-to-charge conversion

To address the spin pumping in the conventional ferromagnetic/“normal” metal systems, we fabricated 6 nm Fe/1–15 nm Rh epitaxial bilayers and determined the g-factor, magnetic anisotropy, and magnetization damping by combining both 0–40 GHz CPW-based frequency-dependent and cavity-based 9.56 GHz in-plane angular-dependent ferromagnetic resonance measurements at room temperature. Auger electron spectroscopy and low-energy electron diffraction show that Rh grows epitaxially on Fe. The epitaxial bilayers exhibit a high spin mixing conductance gmix↑↓=(2.9±0.2)×1019 m−2 and a spin diffusion length in Rhodium λsd=9.0±1.3 nm. This makes Rh comparable to Pt and Pd in terms of spin pumping and spin transport efficiency at room temperature.

Evaluation of temperature dependent vortex pinning properties in strongly pinned YBa2Cu3O7-δ thin films with Y2BaCuO5 nanoinclusions

The pinning of quantized magnetic vortices in superconducting YBa2Cu3O7- δ(YBCO or Y123) thin films with Y2BaCuO5 (Y211) nanoinclusions have been investigated over wide temperature range (4.2–77 K). The concentration of Y211 nanoinclusions has been systematically varied inside YBCO thin films prepared by laser ablation technique using surface modified target approach. Large pinning force density values (Fp ∼ 0.5 TNm−3 at 4.2 K, 9 T) have been observed for the YBCO film with moderate concentration of Y211 nanoinclusions (3.6 area % on ablation target). In addition, uniform enhancement in critical current density (Jc) was observed in the angular dependent Jc measurement of YBCO+Y211 nanocomposite films. Y211 nanoinclusions have been found to be very efficient in pinning the quantized vortices thereby enhancing the in-field Jc values over a wide range of temperature. Increasing the concentration of Y211 secondary phase into Y123 film matrix results into agglomeration of Y211 phase and observed as increased Y211 nanoparticle size. These larger secondary phase nanoparticles are not as efficient pinning centers at lower temperatures as they are at higher temperatures due to substantial reduction of the coherence length at lower temperatures. Investigation of the temperature dependence of Jc for YBCO+Y211 nanocomposite films has been conducted and possible vortex pinning mechanism in these nanocomposite films has been discussed.

Fourfold anisotropic magnetic damping induced by anisotropic spin absorption in amorphous CoFeB/epitaxial IrMn3 bilayers

Magnetic damping rooted in various relaxation processes of spin angular momentum plays a crucial role in determining the energy consumption and the operating speed of emerging spintronic devices. Here, we reported a fourfold anisotropic magnetic damping extrinsically caused by spin current absorption in amorphous ferromagnetic/antiferromagnetic bilayers. The angular dependent broadband ferromagnetic resonance measurements were employed to investigate the effect of interfacial exchange coupling on magnetization dynamics of the CoFeB/IrMn3 bilayers. In addition to the conventional exchange bias, the amorphous CoFeB layer exhibits an induced fourfold magnetic anisotropy along the IrMn3⟨100⟩ axes because of the exchange coupling with the uncompensated IrMn3 moments along IrMn3⟨100⟩ caused by the 3Q antiferromagnetic structure. The magnetic damping of the CoFeB/IrMn3 bilayer also exhibits an obvious fourfold symmetry, which is ascribed to the anisotropic spin absorption caused by the uncompensated IrMn3 moments. The ratio of the fourfold anisotropic magnetic damping decreases dramatically with reducing the interfacial exchange coupling. When the interfacial exchange coupling is isolated by a Cu spacer layer, both the induced magnetic anisotropy and the magnetic damping exhibit a uniaxial symmetry.

Simulation of Colored BIPV Modules Using Angular-Dependent Spectral Responsivity

An accurate energy yield estimation for building-integrated photovoltaic (PV) applications with colored glass under field conditions is a key factor for architects, building planners, and potential investors. The power output of these installations depends not only on the angle of incidence but also on the incident solar spectrum. The aim of this work is to simulate the short-circuit current of PV single-cell laminates with colored solar glass under field conditions. Therefore, we use angular-dependent spectral responsivity measurement data from a physical setup. Test samples with gold-, blue-, blue-green-, and gray-colored solar glass and a reference with standard solar glass, oriented on a tilted surface, are simulated. The results for one month of field validation indicate a good agreement with a relative root mean square error between 1.9% and 2.5% for the test samples. A model comparison reveals larger errors for the blue, blue-green, and gold test samples when the spectral responsivity at normal incidence and the incident angle modifier for broadband direct irradiation are used instead. It is concluded that short-circuit current simulation using indoor characterization from spectrally resolved measurement setups provides improved accuracy that is particularly suitable for bankable energy yield estimates of colored building-integrated PV modules.

Anisotropic Magnetoresistance and Planar Hall Effect in Layered Room-Temperature Ferromagnet Cr1.2Te2

Two-dimensional (2D) van der Waals ferromagnets are regarded as a breakthrough for the 2D spintronics community, which has attracted a great deal of interest in developing low-dimension spintronic devices. Anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) are instrumental in realizing highly sensitive magnetic sensors and nonvolatile memory devices. Despite being discovered in many 2D ferromagnets, most exhibit relatively weak AMR and PHE effects, and their Curie temperature is below room temperature. Here, we report the effects of PHE and AMR at room temperature in the layered ferromagnet of Cr1.2Te2 flakes that exhibit high saturation magnetization and low coercivity, as evidenced by the angular-dependent transport measurements. The low-temperature magnetoresistance behavior of the Cr1.2Te2 flake reveals a truly remarkable 4-fold AMR effect, resulting from the material’s high-term lattice symmetry, which is distinct from the traditional 2-fold AMR. These valuable insights provide a better understanding of high-order AMR in layered magnetic materials. Our findings demonstrate the immense promise of Cr1.2Te2 in driving the development of future 2D spintronic applications that operate at room temperature.

High quantum oscillation frequencies and nontrivial topology in kagome superconductor KV3Sb5 probed by torque magnetometry up to 45 T

Here, we present the Fermi surface properties of the kagome superconductor ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ using torque magnetometry at applied fields up to 45 T and temperatures down to that of liquid $^{3}\mathrm{He}$ (0.32 K). The torque signal shows clear de Haas--van Alphen (dHvA) oscillations with 14 major frequencies ranging from $\ensuremath{\sim}33$ to 2149 T, nine of which are higher frequencies (above 500 T) that have never been reported in ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$. Angular dependence measurements of the dHvA oscillations were carried out to investigate the dimensionality of the Fermi surface. Based on our analysis, several frequencies follow the $1/\mathrm{cos}\phantom{\rule{0.16em}{0ex}}\ensuremath{\theta}$ dependence, where $\ensuremath{\theta}$ is the tilt angle with respect to the applied field direction and oscillations disappear above $\ensuremath{\theta}={60}^{\ensuremath{\circ}}$, which suggest that Fermi surfaces corresponding to these frequencies are quasitwo dimensional. The Berry phase (${\mathrm{\ensuremath{\Phi}}}_{\mathrm{B}}$), determined by constructing a Landau level fan diagram, was found to be ${\mathrm{\ensuremath{\Phi}}}_{\mathrm{B}}\ensuremath{\sim}\ensuremath{\pi}$, which strongly suggests the nontrivial topology of ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$. To explain the experimental results, we carried out band-structure and Fermi-surface calculations using density functional theory (DFT) for both pristine and charge-density wave (CDW) phases. We found that the Fermi surface undergoes severe reconstruction in the CDW phase and, more importantly, our calculation results are in reasonable agreement with the experimentally measured Fermi-surface frequencies. The observation in this paper of very high quantum oscillation frequencies in ${\mathrm{KV}}_{3}{\mathrm{Sb}}_{5}$ and the determination of their detailed Fermi-surface properties, along with the analyses of corresponding DFT calculation results, are crucial for understanding CDW order, unconventional superconductivity, and nontrivial topology in $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}\phantom{\rule{0.28em}{0ex}}(A=\mathrm{K},\mathrm{Rb},$ and Cs), as well as the interplay among them.

Evidences of Topological Surface States in the Nodal-Line Semimetal SnTaS2 Nanoflakes.

Exploring the topological surface state of a topological semimetal by the transport technique has always been a big challenge because of the overwhelming contribution of the bulk state. In this work, we perform systematic angular-dependent magnetotransport measurements and electronic band calculations on SnTaS2 crystals, a layered topological nodal-line semimetal. Distinct Shubnikov-de Haas quantum oscillations were observed only in SnTaS2 nanoflakes when the thickness was below about 110 nm, and the oscillation amplitudes increased significantly with decreasing thickness. By analysis of the oscillation spectra, together with the theoretical calculation, a two-dimensional and topological nontrivial nature of the surface band is unambiguously identified, providing direct transport evidence of drumhead surface state for SnTaS2. Our comprehensive understanding of the Fermi surface topology of the centrosymmetric superconductor SnTaS2 is crucial for further research on the interplay of superconductivity and nontrivial topology.

Optical properties and thermal degradation of NbB2/Nb(BNO)/Al2O3 spectrally selective tandem absorber

The development of any new ceramic absorber demands the evaluation of different performance-limiting properties. In a recently published paper from our research group, we reported the development of NbB2-based new tandem absorber. In our efforts to investigate further potentiality for concentrated solar power applications, this study reports the optical and angular dependent reflectance properties of the NbB2/Nb(BNO)/Al2O3 spectrally selective absorber. The optical properties (extinction coefficient and refractive index) and the dielectric constants of the coatings were determined using spectroscopic ellipsometry analysis. Such analysis together with SCOUT simulation of the reflectance spectrum, confirms the refractive index gradient from the substrate to the top layer. The angular-dependent reflectance measurement demonstrates good solar absorptance (from 8 to 48°). More importantly, the coatings exhibited good thermal stability up to 200 h in vacuum at 500 °C. Extensive transmission electron microscopy analysis reveals the traces of oxygen in the layers. The moderate decrease in absorptance can be rationalised due to the compaction and formation of an oxide layer. Based on the obtained results and earlier published studies, the potential of the NbB2-based coatings as solar selective absorber for concentrated solar power applications is established.

Sn intercalation into the BL/SiC(0001) interface: A detailed SPA-LEED investigation

Growth of epitaxial graphene (EG) with desired properties and formation of new 2D interfaces can be achieved by intercalation of new elements into the carbon buffer layer (BL)/SiC(0001) interface. In this study, we investigated the formation of various ordered Sn-interface structures and, associated with it, the formation of quasi-free monolayer graphene by means of high-resolution spot profile analyzing low energy electron diffraction (SPA-LEED). The analyses of the diffraction patterns and the diffraction spot intensities allowed us to identify various long-range ordered interface structures as a function of the annealing temperature, e.g. (1 × 1), (3×3)R30° and (39×39)R16.1°. The ordering process at the interface and accompanying onset of deintercalation was controlled and monitored by high angular resolution and energy dependent measurements. Besides, for Sn sub-monolayer intercalation coverages, also a (3×3)R30° reconstruction with respect to EG was found, which indicates a broken Kekulé structure of the π-electrons in EG.

Josephson vortices and intrinsic Josephson junctions in the layered iron-based superconductor Ca10(Pt3As8)((Fe0.9Pt0.1)2As2)5

Modulated electronic state due to the layered crystal structures brings about moderate anisotropy of superconductivity in the iron-based superconductors and thus Abrikosov vortices are expected in the mixed state. However, based on the angular and temperature dependent transport measurements in iron-based superconductor Ca10(Pt3As8)((Fe0.9Pt0.1)2As2)5 with T c ≃ 12 K, we find clear evidences of a crossover from Abrikosov vortices to Josephson vortices at a crossover temperature T* ≃ 7 K, when the applied magnetic field is parallel to the superconducting FeAs layers, i.e., the angle between the magnetic field and the FeAs layers θ = 0°. This crossover to Josephson vortices is demonstrated by an abnormal decrease (increase) of the critical current (flux-flow resistance) below T*, in contrast to the increase (decrease) of the critical current (flux-flow resistance) above T* expected for Abrikosov vortices. Furthermore, when θ is larger than 0.5°, the flux-flow resistance and critical current have no anomalous behaviors across T*. These anomalous behaviors can be understood in terms of the distinct transition from the well-pinned Abrikosov vortices to the weakly-pinned Josephson vortices upon cooling, when the coherent length perpendicular to the FeAs layers ξ ⊥ becomes shorter than half of the interlayer distance d/2. These experimental findings indicate the existence of intrinsic Josephson junctions below T* and thus quasi-two-dimensional superconductivity in Ca10(Pt3As8)((Fe0.9Pt0.1)2As2)5, similar to those in the cuprate superconductors.

Strain-engineering of magnetic anisotropy in CoxNi1−x−SrTiO3/SrTiO3 (001) vertically assembled nanocomposites

Ultrathin ${\mathrm{Co}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}$ alloy nanowires vertically embedded in ${\mathrm{SrTiO}}_{3}/{\mathrm{SrTiO}}_{3}\phantom{\rule{0.16em}{0ex}}(001)$ thin films were grown using a self-assembly approach based on sequential pulsed laser deposition. Due to vertical epitaxial coupling of the metallic and oxide phases, a large average tensile strain of up to 4% arises within the nanowires, which is evidenced using a combination of x-ray diffraction and transmission electron microscopy. Macroscopic magnetometry experiments are used to demonstrate that this huge deformation allows us to enhance the uniaxial anisotropy of the nanowires, leading to saturation field in excess of 1 T in the hard direction, large coercive field at low temperature along the easy axis, and to a blocking temperature exceeding 600 K in the case of nanowires with a diameter of 5 nm and 78% Co content. These data are complemented with angular dependent x-ray magnetic circular dichroism measurements at the Co and Ni ${L}_{2,3}$ edges. The value of the magnetic moment was extracted from these measurements by applying sum rules and the anisotropy of the orbital moment was investigated.

Room-Temperature Nonreciprocal Charge Transport in an InAs-Based Rashba Channel

Nonreciprocal charge transport is observed in a non-centrosymmetric system without a ferromagnetic layer. To observe the nonreciprocity of the Rashba system, an InAs-based two-dimensional electron gas channel is utilized and the angular dependent harmonic Hall measurement is performed. From the amplitude of the curve, a nonreciprocal coefficient of 1.36 A−1T−1 is extracted at 1.9 K. While the extracted value of the nonreciprocal coefficient decreases down to 0.44 A−1T−1 at 300 K, we can clearly observe the nonreciprocal charge transport at room temperature. In addition, the independent transport measurements clarify that the amplitude of nonreciprocal coefficient is closely connected with the strength of the Rashba effect.

Distinguishing spin pumping from spin rectification in lateral spin pumping device architectures based on doped organic semiconductors

Over the last two decades organic spintronics has developed into a striving field with exciting reports of long spin diffusion lengths and spin relaxation times in organic semiconductors (OSCs). Easily processed and inexpensive, OSCs are considered a potential alternative to inorganic materials for use in spintronic applications. Spin currents have been detected in a wide range of materials; however, there is still uncertainty over the origin of the signals. Recently, we explored spin transport through an organic semiconductor with lateral spin injection and detection architectures, where the injected spin current is detected nonlocally via spin-to-charge conversion in an inorganic detector. In this work we show that the widely used control experiments like linear power dependence and inversion of the signal with the magnetic field are not sufficient evidence of spin transport and can lead to an incorrect interpretation of the signal. Here, we use in-plane angular dependent measurements to separate pure spin signal from parasitic effects arising from spin rectification. Apart from well established anisotropic magnetoresistance and the anomalous Hall effect, we observe another spurious effect originating in Py and having the same angular symmetry as the inverse spin Hall effect (ISHE), which suggests it might be a self-induced ISHE.

Angular-dependent magnetic properties of chemically synthesized single crystalline Co nanowires

Angular-dependent measurements of magnetic properties could point the way for understating reversal modes of anisotropic nanoobjects for use in next generation of more powerful and permanent information storage devices. However, such measurements have been significantly less considered for chemically synthesized nanowires. Here, single crystalline hexagonal close-packed Co nanowires with an average length and diameter of 220 and 12 nm, respectively, are synthesized using a solvothermal method in a non-polar solvent. The angular-dependent (0° ≤θ ≤ 90°) magnetic properties are carefully studied by hysteresis loop measurements and first-order reversal curve (FORC) analysis after aligning the Co nanowires oriented along [001] direction in epoxy. While randomly oriented Co nanowires have a coercivity (Hc) and squareness (Sq) of 4.3 kOe and 0.54, respectively, they show enhanced magnetic properties (Hc = 7.9 kOe and Sq = 0.78) after alignment at θ = 0°. The FORC analysis indicates the formation of by-products such as nanoparticles and low aspect ratio nanorods in the synthesis of the Co nanowires, which are confirmed by high-resolution transmission electron microscopy. The variation of coercive field distribution (ΔHcFORC) as a function of θ is studied, demonstrating a continuous increase in (ΔHcFORC) for θ > 45°. This indicates that the aligned Co nanowires with high crystallinity may reverse their magnetization through a domain wall mode, being in accordance with the literature on the magnetization reversal mechanism taking place in electrochemically fabricated Co nanowire arrays.

Fermi Surface Structure and Isotropic Stability of Fulde-Ferrell-Larkin-Ovchinnikov Phase in Layered Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

The Fermi surface structure of a layered organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 was determined by angular-dependent magnetoresistance oscillations measurements and band-structure calculations. This salt was found to have two small pockets with the same area: a deformed square hole pocket and an elliptic electron pocket. Characteristic corrugations in the field dependence of the interlayer resistance in the superconducting phase were observed at any in-plane field directions. The features were ascribed to the commensurability (CM) effect between the Josephson vortex lattice and the periodic nodal structure of the superconducting gap in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase. The CM effect was observed in a similar field region for various in-plane field directions, in spite of the anisotropic nature of the Fermi surface. The results clearly showed that the FFLO phase stability is insensitive to the in-plane field directions.

Characterization of an under-development capacitor dosimeter equipped with a silicon x-ray diode.

Herein, we evaluated a capacitor dosimeter under development by a manufacturer, which is designed to monitor the entrance dose in x-ray diagnosis and comprises a silicon x-ray diode (Si-XD), a 0.1 µF capacitor, and a dosimeter dock. The Si-XD is a high-sensitivity photodiode optimized for x-ray detection. The dosimeter was charged to 3.30V using the dock before x-ray irradiation. The charging voltage was reduced by photocurrents flowing through the Si-XD during irradiation, and the discharging voltage was measured. For the fundamental characterization of this capacitor dosimeter, we investigated the x-ray tube-current and tube-voltage dependences of the measured dose using an industrial x-ray tube; the angular dependence was also investigated. A commercially available semiconductor dosimeter (RaySafe ThinX) was used for dose calibration. The doses were proportional to the tube current at a constant tube voltage of 100kV and increased with increasing tube voltage at a constant tube current of 1.0 mA. The dose difference with respect to the commercially available semiconductor dosimeter was within 1.0% when the tube current was varied and it was within 3.0% when the tube voltage was varied. In the angular dependence measurement, a difference of up to 6.0% was observed as the angle varied from 0° to 355° in steps of 5°. The dose-calibration results indicated that the determination of the initial charging voltage was important for dose conversion using the capacitor dosimeter.

Metallic capped quasi-two-dimensional electron gas in a SrTiO3-based heterostructure

Two-dimensional electron gas (2DEG) in SrTiO3 (STO)-based heterostructures has been a subject of intense scientific interest in recent years. In this work, the metallic transition metal dichalcogenides ZrTe2 was grown on STO by pulsed laser deposition and AlN was subsequently deposited as a protection layer. The high-resolution transmission electron microscopy and electron energy loss spectroscopy results demonstrated the system as a multilayer structure of AlN/ZrTe2/ZrO2/STO due to interface redox reactions and implied a conductive STO surface. The remarkable Shubnikov–de Haas oscillations detected by angular dependent magnetotransport measurements reveal clear evidence of a high mobility quasi-2DEG in the STO-based interface. Moreover, evidence for extra carriers with three-dimensional features is observed implying the multiband contributions, which provide an explanation for some anomalous behavior in STO-based heterostructures. In addition, the thickness dependence study suggests the charge transfer effect between the capping metallic topological material ZrTe2 and the interfacial 2DEG. This work provides insight into the intrinsic electronic structure of STO-based heterostructures, and the integrated systems can serve as a platform for studying the interplay of the 2DEG with attractive materials as well as developing practical device applications.

Spin Current Transport in Hybrid Pt/Multifunctional Magnetoelectric Ga0.6Fe1.4O3 Bilayers

The low power manipulation of magnetization is currently a highly sought-after objective in spintronics. Non ferromagnetic large spin-orbit coupling heavy metal (NM) / ferromagnet (FM) heterostructures offer interesting elements of response to this issue, by granting the manipulation of the FM magnetization by the NM spin Hall effect (SHE) generated spin current. Additional functionalities, such as the electric field control of the spin current generation, can be offered using multifunctional ferromagnets. We have studied the spin current transfer processes between Pt and the multifunctional magnetoelectric Ga0.6Fe1.4O3 (GFO). In particular, via angular dependent magnetotransport measurements, we were able to differentiate between magnetic proximity effect (MPE)-induced anisotropic magnetoresistance (AMR) and spin Hall magnetoresistance (SMR). Our analysis shows that SMR is the dominant phenomenon at all temperatures and is the only one to be considered near room temperature, with a magnitude comparable to those observed in Pd/YIG or Pt/YIG heterostructures. These results indicate that magnetoelectric GFO thin films show promises for achieving an electric-field control of the spin current generation in NM/FM oxide-based heterostructures.