Measurements Of Angular Dependence Research Articles

Effect of CoSi2 interfacial layer on the magnetic properties of Si|CoSi2|Sm-Co thin films

Abstract Magnetic thin films with a layer sequence of Si|CoSi2|Sm-Co were grown by direct sputter deposition at elevated temperatures, through interfacial diffusion between Si (1 0 0) substrate and the overlying Sm-Co layer. HR-TEM analysis revealed the occurrence of CoSi2-interfacial layer close to the Si-substrate surface, with controllable thicknesses of ~20 and 35 nm at deposition temperatures: 450 and 500 °C, respectively. XRD studies confirmed the crystallization of Sm2Co17 and SmCo5 magnetic phases accompanied by the other phases such as CoSi2 and SmCoSi2 due to the intermixing of Co and Si -atoms at higher deposition temperatures. The measured coercivity values are found to be increased from 8.7 to 11.6 kOe at higher CoSi2-layer thickness. The angular-dependent hysteresis measurements demonstrated a distinct isotropic and uniaxial magnetic anisotropy characteristics for the Sm-Co films consisting of 35 and 20-nm thick CoSi2 interfacial layers, respectively and the associated magnetization reversal mechanisms are discussed using the Stoner-Wohlfarth model. The temperature coefficients of remanence (α) and coercivity (β) were determined from the temperature-dependent hysteresis curves. The Sm-Co films consisting of 35-nm thick CoSi2-layer exhibited a better thermal stability with ‘α’ and ‘β’ values of 0.35 ± 0.05%/°C and −0.13 ± 0.02%/°C, respectively. The results of present study provide splendid opportunities for exploiting the potential of CoSi2 as an under layer, for growing the Sm-Co films towards high-temperature applications.

Evidence of anisotropic Landau level splitting in topological semimetal ZrSiS under high magnetic fields

Magneto-transport study has been performed in topological semimetal ZrSiS single crystals under high pulsed magnetic fields. Obvious dependence of Landau level splitting on temperature and angular was investigated. The strong three-dimensional anisotropic nature of Landau level splitting under high pulsed magnetic fields was revealed by the angular dependent measurements, in which the orbital contribution is more dominant than Zeeman splitting. Our studies provide more insights into the physical properties of topological semimetals ZrSiS and shed light on future spintronic applications of ZrSiS.

Two-Fold Reduction of <italic>J</italic>cAnisotropy in FeSe0.5Te0.5Films Using Low-Energy Proton Irradiation

High in-field performance and low anisotropy of critical current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> are important for superconducting wires/tapes in rotating machine and magnet applications. Here, we report measurements of angular dependence of critical current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in proton-irradiated FeSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> (FST) films at magnetic field up to 35 T. We observed two-fold reduction in the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> anisotropy of FST films at 4.2 K and 15 Tesla magnetic field by irradiation with low-energy (190 keV) proton. In light of recent demonstration of roll-to-roll irradiation process successfully incorporated in the standard 2G HTS long length production wire, low-energy proton irradiation can be a practical solution to enhance the performance of iron-based superconducting wires and tapes, as low-energy ion sources are inexpensive to operate and are readily available commercially.

Experimental Measurement of Angular and Overlap Dependence of Conduction between Carbon Nanotubes of Identical Chirality and Diameter

Measurement of the angular and overlap dependence of the conduction between two identical carbon nanotubes (CNTs), with the same diameter and chirality, has only been possible through theoretical calculations; however, our observation of increased resistance adjacent to the junction between two CNTs facilitates such measurements. Since electrical resistance was found to increase with increased diameter ratio, applying 10 V to one of dissimilar diameter CNTs results in cleavage at the junction. Manipulation of the resulting identical CNTs (created by cutting a single CNT) allows for the direct measurement of the angular and parallel overlap conduction. Angular (13° < θ < 63°) dependence shows two minima (22° and 44°) and a maximum at 30°, and conduction between parallel CNTs increases with overall tip separation but shows a sinusoidal relationship with contact length, consistent with the concept of atomic scale registry.

Ferromagnetic Co3Sn2S2 thin films fabricated by co-sputtering

We synthesized the magnetic Weyl semimetal candidate Co3Sn2S2 as a thin film using the co-sputtering technique. By adjusting the film composition using a sulfur-rich SnS1.5 target with Co metal chips attached, we obtained highly crystallized, single-phase Co3Sn2S2 films. The films showed a ferromagnetic transition around 180 K with perpendicular remanent magnetization. We observed the anomalous Hall effect with a tangent of Hall angle of 0.20 at 130 K, as previously reported for the bulk single crystals. Angular dependence measurements suggested that the magnetization reversal process governed by the domain wall motion leads to a large coercive field in the films.

Magnetic anisotropy and spin-polarized two-dimensional electron gas in the van der Waals ferromagnet Cr2Ge2Te6

We report a comprehensive experimental investigation on the magnetic anisotropy in bulk single crystals of Cr$_2$Ge$_2$Te$_6$, a quasi-two-dimensional ferromagnet belonging to the family of magnetic layered transition metal trichalcogenides that have attracted recently a big deal of interest with regard to the fundamental and applied aspects of two-dimensional magnetism. For this purpose electron spin resonance (ESR) and ferromagnetic resonance (FMR) measurements have been carried out over a wide frequency and temperature range. A gradual change in the angular dependence of the ESR linewidth at temperatures above the ferromagnetic transition temperature $T_{\rm c}$ reveals the development of two-dimensional spin correlations in the vicinity of $T_{\rm c}$ thereby proving the intrinsically low-dimensional character of spin dynamics in Cr$_2$Ge$_2$Te$_6$. Angular and frequency dependent measurements in the ferromagnetic phase clearly show an easy-axis type anisotropy of this compound. Furthermore, these experiments are compared with simulations based on a phenomenological approach, which takes into account results of static magnetization measurements as well as high temperature $g$ factors obtained from ESR spectroscopy in the paramagnetic phase. As a result the determined magnetocrystalline anisotropy energy density (MAE) $K_U$ is $(0.48 \pm 0.02) \times10^6$ erg/cm$^3$. This analysis is complemented by density functional calculations which yield the experimental MAE value for a particular value of the electronic correlation strength $U$. The analysis of the electronic structure reveals that the low-lying conduction band carries almost completely spin-polarized, quasi-homogeneous, two-dimensional states.

Polymer-assisted surface decoration for critical current enhancement in YBa2Cu3O7−x films

In this study, chemically decorated surfaces are employed as tools for Artificial Pinning Centres (APC) introduction in superconducting YBa2Cu3O7−x (YBCO) films. Self-assembled oxide nanostructures are grown on crystalline substrates via a very versatile and low-cost chemical technique called Polymer Assisted Deposition (PAD). Such decorated templates are used, in a second step, as substrates for YBCO film growth via Metal Organic Decomposition (MOD) or Pulsed Laser Deposition (PLD). The aim of the structures is to produce in the superconducting matrix strain and/or defects that should act as APCs and therefore enhance the transport properties of the samples. The oxides selected for the decoration are commonly used for the introduction of artificial pinning centres in YBCO: BaZrO3 and ZrO2. The decorated surfaces are analyzed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). YBCO films have been characterized via SEM, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), DC resistivity and critical current measurements. The results show that the nanostructures are stable and that they can efficiently introduce strain and stacking faults in the film. This causes an increase in the value of the critical current density Jc and better in-field behaviour in all the investigated field range, compared to the analogous film grown on a standard substrate, especially for chemically derived YBCO. Also Jc angular dependence measurements, Jc(θ), show an isotropic enhancement of the critical current for every angle of application of the field.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Effects of film thickness and annealing on the magnetic properties of GaMnAsP ferromagnetic semiconductor

We have investigated the magnetic properties of ferromagnetic semiconductor GaMnAsP films with two different thicknesses. Temperature scans of the resistance revealed that the Curie temperature was higher in the 50-nm GaMnAsP layer than in the 16-nm layer, and was increased in both layers after annealing. The Hall effect was measured during the magnetization reversal process to identify the anisotropy of the films. The hysteresis observed from the as-grown samples in anomalous Hall resistance measurements implied the presence of out-of-plane magnetic anisotropy in both samples. The out-of-plane magnetic anisotropy in both samples became much stronger after thermal annealing. Quantitative values of the magnetic anisotropy of the GaMnAsP films were obtained from angular dependent Hall effect measurements. By constructing magnetic anisotropy energy diagrams for the films, we clearly show the change of magnetic anisotropy depending on the film thickness and thermal annealing in GaMnAsP films.

Excessive applicator radiation leakage for a common therapeutic kilovoltage system.

The objective of this work is to characterise out- of- field leakage radiation emanating from clinical applicators of the WOmed T-200 kilovoltage therapy machine. To identify points of leakage, radiosensitive film was affixed to the walls and base plate of each applicator. Quantitative assessment of leakage radiation was conducted with a 0.23 cm3 ionisation chamber following the International Electrotechnical Commission standard. Film was also used to illustrate leakage distribution in the patient plane. Angular and energy dependences of the leakage radiation were quantified as well as a two-dimensional leakage profile in the plane parallel to one applicator. Leakage was found when the diameter of primary collimator of the kV tube exceeded the external dimension of the applicator wall. In the patient plane all applicators showed similar leakage rates with the leakage distribution dependent upon applicator design. Mean patient plane leakage was 1.37% of central axis air kerma rate, exceeding the 0.5% limit specified in the standard. Leakage was shown to be profoundly energy dependent with maximum leakage of 11.8% for the 200 kV beam, 1.3% for 150 kV and 0.2% for 100 kV. Angular dependence measurements showed a 10.3% change in leakage between the minimum and maximum positions. The combination of shielding thickness, primary collimator design and applicator dimensions permits unwanted radiation to contribute dose outside the treatment field when energies ≥150 kV are used. Even carefully designed modern kv therapy systems can exhibit leakage in some areas. Thorough assessment of leakage is needed prior to release for clinical use.

Interface morphology effect on the spin mixing conductance of Pt/Fe3O4 bilayers

Non-magnetic (NM) metals with strong spin-orbit coupling have been recently explored as a probe of interface magnetism on ferromagnetic insulators (FMI) by means of the spin Hall magnetoresistance (SMR) effect. In NM/FMI heterostructures, increasing the spin mixing conductance (SMC) at the interface comes as an important step towards devices with maximized SMR. Here we report on the study of SMR in Pt/Fe3O4 bilayers at cryogenic temperature, and identify a strong dependence of the determined real part of the complex SMC on the interface roughness. We tune the roughness of the Pt/Fe3O4 interface by controlling the growth conditions of the Fe3O4 films, namely by varying the thickness, growth technique, and post-annealing processes. Field-dependent and angular-dependent magnetoresistance measurements sustain the clear observation of SMR. The determined real part of the complex SMC of the Pt/Fe3O4 bilayers ranges from 4.96 × 1014 Ω−1 m−2 to 7.16 × 1014 Ω−1 m−2 and increases with the roughness of the Fe3O4 underlayer. We demonstrate experimentally that the interface morphology, acting as an effective interlayer potential, leads to an enhancement of the spin mixing conductance.

Room Temperature Coherently Coupled Exciton-Polaritons in Two-Dimensional Organic-Inorganic Perovskite.

Two-dimensional (2D) organic-inorganic perovskite semiconductors with natural multiquantum well structures and confined 2D excitons are intriguing for the study of strong exciton-photon coupling, due to their large exciton binding energy and oscillation strength. This strong coupling leads to a formation of the half-light half-matter bosonic quasiparticle called exciton-polariton, consisting of a linear superposition state between photonic and excitonic states. Here, we demonstrate room temperature strong coupling in exfoliated wavelength-tunable 2D organic-inorganic perovskite semiconductors embedded into a planar microcavity, exhibiting large energetic splitting-to-line width ratios (>34.2). Angular-dependent spectroscopy measurements reveal that hybridized polariton states act as an ultrafast and reversible energy oscillation, involving 2D perovskite exciton, cavity modes (CM), and Bragg modes of the distributed Bragg reflector. Meanwhile, sizable hybrid particles dominantly couple to the measured optical field through the CMs. Our findings advocate a considerable promise of 2D organic-inorganic perovskite to explore fundamental quantum phenomena such as Bose-Einstein condensation, superfluidity, and exciton-polariton networks.

Spectral and directional properties of elliptical quantum-dot microlasers

We have fabricated microdisk lasers of colloidal quantum dots in circular and elliptical forms with different aspect ratios. By characterizing the laser emission spectrum under optical pumping and through mode simulation calculations, we demonstrate that the elliptical resonators can display two sets of whispering-gallery modes that interact to varying degrees depending on the aspect ratio. This causes significant mode splitting in the emission spectra when the mode interaction is at maximum. We also performed angular-dependent laser emission measurements for characterizing the emission pattern of the microlasers. We found that the emission pattern becomes less isotropic and more directional as the boundary deviates further from circular symmetry. In addition, we demonstrate that the emission directional properties of these microlasers can be further tailored by coupling pairs of elliptical microcavities together in different manners, where the long or short elliptical axis interacts most strongly.

Superconducting and normal-state anisotropy of the doped topological insulator Sr0.1Bi2Se3

SrxBi2Se3 and the related compounds CuxBi2Se3 and NbxBi2Se3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with Tc ~3 K in SrxBi2Se3 arises upon intercalation of Sr into the layered topological insulator Bi2Se3. Here we elucidate the anisotropy of the normal and superconducting state of Sr0.1Bi2Se3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magnetic properties of Sr0.1Bi2Se3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. Our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in SrxBi2Se3.

Dosimetric characterisation of the optically-stimulated luminescence dosimeter in cobalt-60 high dose rate brachytherapy system.

This study investigates the characteristics and application of the optically-stimulated luminescence dosimeter (OSLD) in cobalt-60 high dose rate (HDR) brachytherapy, and compares the results with the dosage produced by the treatment planning system (TPS). The OSLD characteristics comprised linearity, reproducibility, angular dependence, depth dependence, signal depletion, bleaching rate and cumulative dose measurement. A phantom verification exercise was also conducted using the Farmer ionisation chamber and in vivo diodes. The OSLD signal indicated a supralinear response (R2 = 0.9998). It exhibited a depth-independent trend after a steep dose gradient region. The signal depletion per readout was negligible (0.02%), with expected deviation for angular dependence due to off-axis sensitive volume, ranging from 1 to 16%. The residual signal of the OSLDs after 1day bleached was within 1.5%. The accumulated and bleached OSLD signals had a standard deviation of ± 0.78 and ± 0.18Gy, respectively. The TPS was found to underestimate the measured doses with deviations of 5% in OSLD, 17% in the Farmer ionisation chamber, and 7 and 8% for bladder and rectal diode probes. Discrepancies can be due to the positional uncertainty in the high-dose gradient. This demonstrates a slight displacement of the organ at risk near the steep dose gradient region will result in a large dose uncertainty. This justifies the importance of in vivo measurements in cobalt-60 HDR brachytherapy.

Estimation of parameters of gassy layer in sediment in shallow water using measurement of angular dependence and spectrum of reflection coefficient of wide-band signals

Method of estimation of gassy layer parameters in sediment (sound speed and thickness) on the base of measurement of angular and frequency dependencies reflection coefficient of wideband signals is presented. Experiments were carried out in Lake Kinneret (Israel), which is characterized by remarkable organic content in sediment producing methane bubbles. Direct chemical, biological analysis and usage of frozen cores show comparatively narrow layer (a few tens of cm) changing in dependence on season. Principal point for acoustical method is low sound speed in bubble layer (up to 300–400 m/s) and big reflection coefficient from the corresponding half-space (0.6–0.7 for vertical incident). Due to narrow gassy layer, there should be half wavelength resonances at the corresponding frequencies. In experiments, wideband signals were used (500–2500 Hz) and receiving system: single hydrophone (1 m from source) and vertical line array. Estimation of layer’s parameters was carried out using measured reflection coefficient as a function of frequency and angle of reflection. Resonance frequencies were 800 Hz and 1600 Hz. The corresponding analysis of data give values of thickness 25–30 cm, with the sound speed in layer 400–450 m/c. Results are compared with experimental data obtained by direct measurements. [Work was supported by ONRG and ISF.]

Interface-induced spin Hall magnetoresistance enhancement in Pt-based tri-layer structure

In this study, we integrated bilayer structure of covered Pt on nickel zinc ferrite (NZFO) and CoFe/Pt/NZFO tri-layer structure by pulsed laser deposition system for a spin Hall magnetoresistance (SMR) study. In the bilayer structure, the angular-dependent magnetoresistance (MR) results indicate that Pt/NZFO has a well-defined SMR behavior. Moreover, the spin Hall angle and the spin diffusion length, which were 0.0648 and 1.31 nm, respectively, can be fitted by changing the Pt thickness in the longitudinal SMR function. Particularly, the MR ratio of the bilayer structure (Pt/NZFO) has the highest changing ratio (about 0.135%), compared to the prototype structure Pt/Y3Fe5O12 (YIG) because the NZFO has higher magnetization. Meanwhile, the tri-layer samples (CoFe/Pt/NZFO) indicate that the MR behavior is related with CoFe thickness as revealed in angular-dependent MR measurement. Additionally, comparison between the tri-layer structure with Pt/NZFO and CoFe/Pt bilayer systems suggests that the SMR ratio can be enhanced by more than 70%, indicating that additional spin current should be injected into Pt layer.

Spin Hall magnetoresistance in the non-collinear ferrimagnet GdIG close to the compensation temperature

We investigate the spin Hall magnetoresistance (SMR) in a gadolinium iron garnet (GdIG)/platinum (Pt) heterostructure by angular dependent magnetoresistance measurements. The magnetic structure of the ferromagnetic insulator GdIG is non-collinear near the compensation temperature, while it is collinear far from the compensation temperature. In the collinear regime, the SMR signal in GdIG is consistent with the usual relation well established in the collinear magnet yttrium iron garnet, with the angle between magnetization and spin Hall spin polarization direction. In the non-collinear regime, both an SMR signal with inverted sign and a more complex angular dependence with four maxima are observed within one sweep cycle. The number of maxima as well as the relative strength of different maxima depend strongly on temperature and field strength. Our results evidence a complex SMR behavior in the non-collinear magnetic regime that goes beyond the conventional formalism developed for collinear magnetic structures.

The Nitrogen Acceptor in 2H‐Polytype Synthetic MoS2: Frequency and Temperature Dependent ESR Analysis

In extending on recent electron spin resonance (ESR) work which has revealed the N acceptor (N substituting for S site) in 2H‐polytype bulk synthetic MoS2, the dopant is extensively analyzed in terms of its frequency, temperature (T), and magnetic field B angular dependent ESR spectral characteristics. For B∥c‐axis, the multi‐frequency analysis confirms the ESR spectrum as being composed of a 14N hyperfine (hf) triplet with hf splitting constant A∥ = 14.7 ± 0.2 G (B∥c‐axis) and making up ≈74% of the total spectrum intensity, superimposed on a central line centered at about equal g‐value [g∥ = 2.032(2)]. The presence of the latter signal, points to some non‐uniformity in dopant distribution, that is, clustering, with about ≈26% of the total N response not originating from N incorporated in the preferred “isolated” dopant configuration. Angular dependent measurements reveal distinct anisotropy of the hf matrix, whereas ESR probing over a wide T‐range exposes drastic signal broadening with increasing T above ≈150 K. Detailed study of the N acceptor signal intensity versus T at Q‐band reveals an activation energy Ea = 50 ± 10 meV, herewith consolidating the value reported initially. Besides unveiling the S‐site substitutional N impurity as an appropriate p‐type dopant for MoS2, the total of the ESR work establishes a basic frame of the N acceptor ESR characteristics, giving way for further in‐depth theoretical perusal.

Annealing and thickness effects on magnetic properties of Co2FeAl alloy films

Co2FeAl (CFA) films in a wide thickness range between 2 and 100 nm are sputtered at room temperature. Perpendicular magnetic anisotropy (PMA) is achieved in the annealed structure of Pd/CFA/MgO with CFA thickness ranging between 2.3 and 4.9 nm. PMA as high as 2 × 106 erg/cm3 is demonstrated in the structures annealed in the temperature range between 300 and 350 °C. Positive contributions to the PMA made by the interfaces of Pd/CFA and CFA/MgO are identified. For the as-deposited structure of MgO/CFA/Ta with thick CFA alloy up to 5 nm or above a high effective saturation magnetization of 983.9 ± 30.1 emu/cc is derived from the fitting and an in-plane uniaxial magnetic anisotropy of 104 erg/cm3 in magnitude is revealed by angular dependent magnetic measurements. In addition to the increase in saturation magnetization, a fourfold cubic magnetic anisotropy is found to develop with annealing, in line with the improvement of the crystalline structure confirmed by X-ray diffraction measurements. Out results provide some useful information for the design of the CFA-based magnetoelectronic devices.