Spin Rotation Research Articles

Giant magnetoimpedance effect in electrodeposited CoNiFe/Cu composite wire: Experimental study and analytical modelling

Study of giant magnetoimpedance effect (GMI) in electrodeposited CoNiFe/Cu composite wire is reported in the intermediate frequency region (10 kHz–10 MHz). The room temperature M–H curve of the sample reveals that the magnetic softness is independent of the film thickness(t). The changes in GMI value is attributed to the geometric effect caused by change of film thickness. To justify this claim, a hybrid model for circumferential permeability is proposed by combining the effect of domain wall motion(μdw), spin rotation (μrot) and local dispersion of anisotropy. The spectra of circumferential permeability is modelled with domain wall relaxation with continuous distribution of relaxation times. The spin rotation part of circumferential permeability is formulated using linearized Landau–Lifshitz–Gilbert (LLG) equation with Bloch–Bloembergen damping term and dispersion of anisotropy field. The proposed model is able to reproduce all the experimental results using single set of material parameters.

Edge physics at the deconfined transition between a quantum spin Hall insulator and a superconductor

We study the edge physics of the deconfined quantum phase transition (DQCP) between a spontaneous quantum spin Hall (QSH) insulator and a spin-singlet superconductor (SC). Although the bulk of this transition is in the same universality class as the paradigmatic deconfined Neel to valence-bond-solid transition, the boundary physics has a richer structure due to proximity to a quantum spin Hall state. We use the parton trick to write down an effective field theory for the QSH-SC transition in the presence of a boundary. We calculate various edge properties in an N\to\inftyN→∞ limit. We show that the boundary Luttinger liquid in the QSH state survives at the phase transition, but only as ``fractional’’ degrees of freedom that carry charge but not spin. The physical fermion remains gapless on the edge at the critical point, with a universal jump in the fermion scaling dimension as the system approaches the transition from the QSH side. The critical point could be viewed as a gapless analogue of the quantum spin Hall state but with the full SU(2)SU(2) spin rotation symmetry, which cannot be realized if the bulk is gapped.

Towards the first direct measurement of the dynamic viscosity of gaseous tritium at cryogenic temperatures

Accurate values for the viscosity of the radioactive hydrogen isotope tritium (T2) at cryogenic temperatures are unavailable. Values for tritium found in literature are based on extrapolation by mass ratios as well as an empirical factor derived from hydrogen (H2) and deuterium (D2) viscosity measurements, or classical kinetic theory which does not handle quantum effects. Accurate data of the tritium viscosity will help to improve the modelling of the viscosity of diatomic molecules and can be used as a test of their interaction potentials.With this contribution we report a major step towards a fully tritium and cryogenic temperature compatible setup for the accurate measurement of the viscosity of gases, using a spinning rotor gauge (SRG) at the Tritium Laboratory Karlsruhe. After calibration with helium, measurements with hydrogen and deuterium conducted at room temperature agree with literature values within 2%. The performance at liquid nitrogen (LN2) temperature has been successfully demonstrated with a second setup in a liquid nitrogen bath. Again after calibration with helium at LN2 temperature, the viscosities of H2 and D2 were determined and are in agreement with literature to about 2%.

Excited-state spin-resonance spectroscopy of V{}_{{{{{{{{rm{B}}}}}}}}}^{-} defect centers in hexagonal boron nitride

The recently discovered spin-active boron vacancy (V{}_{{{{{{{{rm{B}}}}}}}}}^{-}) defect center in hexagonal boron nitride (hBN) has high contrast optically-detected magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state that shows promise as a quantum sensor. Here we report temperature-dependent ODMR spectroscopy to probe spin within the orbital excited-state. Our experiments determine the excited-state spin Hamiltonian, including a room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that of the ground-state. We confirm that the resonance is associated with spin rotation in the excited-state using pulsed ODMR measurements, and we observe Zeeman-mediated level anti-crossings in both the orbital ground- and excited-state. Our observation of a single set of excited-state spin-triplet resonance from 10 to 300 K is suggestive of symmetry-lowering of the defect system from D3h to C2v. Additionally, the excited-state ODMR has strong temperature dependence of both contrast and transverse anisotropy splitting, enabling promising avenues for quantum sensing.

Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth‐Resolved Muon Spin Spectroscopy

AbstractAs devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth‐resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se2 absorber and various buffer layers are investigated using low‐energy muon spin rotation (μSR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long‐range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath‐deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry‐deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy μSR spectroscopy for microscopic interfacial studies of multilayer systems.

Magnetic Losses in Soft Ferrites

We review the basic phenomenology of magnetic losses from DC to 1 GHz in commercial and laboratory-prepared soft ferrites considering recent concepts regarding their physical interpretation. This is based, on the one hand, on the identification of the contributions to the magnetization process provided by spin rotations and domain walls and, on the other hand, the concept of loss separation. It additionally contemplates a distinction between the involved microscopic dissipation mechanisms: spin damping and eddy currents. Selected experimental results on the broadband behavior of complex permeability and losses in Mn-Zn ferrites provide significant examples of their dependence on sintering methods, solute elements, and working temperature. We also highlight the peculiar frequency and temperature response of Ni-Zn ferrites, which can be heavily affected by magnetic aftereffects. The physical modeling of the losses brings to light the role of the magnetic anisotropy and the way its magnitude distribution, affected by the internal demagnetizing fields, acts upon the magnetization process and its dependence on temperature and frequency. It is shown that the effective anisotropy governs the interplay of domain wall and rotational processes and their distinctive dissipation mechanisms, whose contributions are recognized in terms of different loss components.

Depth-Resolved Study of the SiO<sub>2</sub>- SiC Interface Using Low-Energy Muon Spin Rotation Spectroscopy

In this work, the interface between 4H-SiC and thermally grown SiO2 is studied using low energy muon spin rotation (LE-μSR) spectroscopy. Samples oxidized at 1300 °C were annealed in NO or Ar ambience and the effect of the ambience and the annealing temperature on the near interface region is studied in a depth resolved manner. NO-annealing is expected to passivate the defects, resulting in reduction of interface traps, which is confirmed by electrical characterization. Introduction of N during annealing, to the SiC matrix, results in a thin, carrier rich region close to the interface leading to an increase in the diamagnetic asymmetry. Annealing in an inert environment (Ar) seems to have much lesser impact on the electrical signal, however the μSR shows a reduced paramagnetic asymmetry, indicating a narrow region of low mobility at the interface.

Hydrogen-Ti<sup>3+</sup> Complex as a Possible Origin of Localized Electron Behavior in Hydrogen-Irradiated SrTiO<sub>3</sub>

A recent muon spin rotation ($\mu^+$SR) study on a paramagnetic defect complex formed upon implantation of $\mu^+$ pseudo-proton into SrTiO$_3$ is reviewed with a specific focus on the relation with experimental signatures of coexisting delocalized and localized electrons in hydrogen-irradiated metallic SrTiO$_3$ films. The paramagnetic defect complex, composed of interstitial $\mu^+$ and Ti$^{3+}$ small polaron, is characterized by a small dissociation energy of about 30 meV. Density functional theory (DFT) calculations in the generalized gradient approximation (GGA) +$U$ scheme for a corresponding hydrogen defect complex reveal that a thermodynamic donor level associated with electron transfer from an H$^+$-Ti$^{3+}$ complex to the conduction band can form just below the conduction band minimum for realistic $U$ values. These findings suggest that the coexistence of delocalized and localized electrons can be realized in hydrogen-irradiated SrTiO$_3$ in electron-rich conditions.

Identifying the mechanism of hard magnet coercivity by its angular dependence

We completed the analytical framework of determining the angular dependence of coercivity for exchange-coupled phases connected with sharp interfaces in one-dimensional micromagnetics. For various thicknesses of soft phase in a hard matrix, the two types of angular dependence of coercivity, with or without a local minimum, were demarcated and illustrated as a phase diagram. The appearance or absence of a local minimum was confirmed as a sign of whether the switching was dominated by the spin rotation or by the depinning of the domain wall. The mechanism could transform from the former to the latter if the coupling ratio between soft and hard phases, ${\ensuremath{\varepsilon}}_{AM}={A}_{s}{M}_{s}/{A}_{h}{M}_{h}$, was increased. The results explained the transformation of angular dependence curves reported in Nd-Fe-B-based permanent magnets.

Dynamic Strain Reconstruction of Rotating Blades Based on Tip Timing and Response Transmissibility

Abstract Dynamic strain of rotating blades is critical in turbomachinery health monitoring and residual life evaluation. Though the blade tip timing (BTT) technique is promising to replace traditional strain gages, the lack of effective strain transformation through BTT hinders the implementation. In this paper, a noncontact dynamic strain reconstruction method of rotating blades is proposed based on the BTT technique and response transmissibility. First, the displacement-to-strain transmissibility (DST) considering rotational speed is derived from the frequency response functions based on blade mode shapes. A quadratic polynomial function of DST with respect to the rotational speed is provided to calibrate DST in blade rotational state. Second, the blade-tip displacement in resonance is obtained by BTT measurement and the Circumferential Fourier Fit processing method. Third, the dynamic strains of critical points on blades are calculated using the DST in conjunction with the tip displacement amplitude. In this paper, to validate the proposed method, acceleration and deceleration experiments, including both BTT and strain gages, are conducted on a spinning rotor rig. Experimental results demonstrate that the reconstructed dynamic strains of different positions on the rotating blades correspond well to the results measured by strain gages. The mean relative error between the reconstructed and measured results is generally within 8%.

High resolution spectroscopy of the [formula omitted] band of the [formula omitted]ClO2 free radical: Spin–rotation–vibration interactions

The high resolution spectrum of the ν1+ν3 band of the 35ClO2 free radical was recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer and theoretically analysed with an improved theoretical basis including the reduced effective spin–rotation Hamiltonian (which takes into account sixth order operators describing spin–rotational interactions) and a newly created computer code ROVDES for the ro–vibrational spectra of open–shell free radicals. About 2600 spin–ro–vibrational transitions with the values Nmax=59 and Kamax=17 (being about 2.4 times higher in comparison with the number of assigned transitions known in the literature) were assigned to the ν1+ν3 band of 35ClO2 and 1049 spin–ro–vibrational energies (produced only from unblended non–saturated and not very weak experimental lines) of the (101) upper vibrational state were obtained. A set of 30 varied parameters of the effective spin–rotation–vibration Hamiltonian of the (101) vibrational state (vibrational energy, 17 rotational and centrifugal distortion parameters and 12 are spin–rotational ones) was determined from the weighted fit of parameters of the effective spin–rotational Hamiltonian in A-reduction and Ir-representation. The obtained set of parameters reproduces the initial 1049 “experimental” upper state energies with the drms=2.5×10-4 cm−1 which is close to the experimental uncertainty of the recorded spectra and is almost 70 times higher in comparison with the analogous reproduction of the same initial upper energies with the use of parameters from (J.Mol.Spectrosc.,158,347-356(1993)).

Simulation studies for upgrading a high-intensity surface muon beamline at Paul Scherrer Institute

The $\ensuremath{\mu}\mathrm{E}4$-LEM beamline at Paul Scherrer Institute (PSI, Switzerland) is a special muon beamline combining the hybrid-type surface muon beamline $\ensuremath{\mu}\mathrm{E}4$ with the low-energy muon (LEM) facility and delivers ${\ensuremath{\mu}}^{+}$ with tunable energy up to 30 keV for low-energy muon spin rotation (LE-$\ensuremath{\mu}\mathrm{SR}$) experiments. We investigate a possible upgrade scenario for the surface muon beamline $\ensuremath{\mu}\mathrm{E}4$ by replacing the last set of quadrupole triplets with a special solenoid to obtain 1.4 times the original beam intensity on the LEM muon moderator target. In order to avoid the muon beam intensity loss at the LEM spectrometer due to the stray magnetic field of the solenoid, three kinds of solenoid models have been explored and the stray field of the solenoid at the LEM facility is finally reduced to the magnitude of the geomagnetic field. A more radical design, ``Super-$\ensuremath{\mu}\mathrm{E}4$,'' has also been investigated for further increasing the brightness of the low-energy muon beam, where we make use of the current $\ensuremath{\mu}\mathrm{E}4$ channel and all sets of quadrupole triplets are replaced by large aperture solenoids. Together with the new slanted muon target E, at least 2.9 times the original muon beam intensity can be expected in the Super-$\ensuremath{\mu}\mathrm{E}4$ beamline. Our work demonstrates the feasibility of upgrading surface muon beamlines by replacing quadrupole magnets with normal-conducting solenoids, resulting in higher muon rates and smaller beam spot sizes.

Spin-liquid signatures in the quantum critical regime of pressurized CePdAl

CePdAl is a prototypical frustrated Kondo lattice with partial long-range order (LRO) at ${T}_{\mathrm{N}}=2.7$ K. Previous bulk experiments under hydrostatic pressure found signatures for a quantum critical regime that extends from ${p}_{\mathrm{c}}\ensuremath{\approx}0.9$ GPa, where LRO disappears, up to $\ensuremath{\sim}1.7$ GPa. We employed extensive muon spin relaxation and rotation experiments under pressure. The continuous and complete suppression of LRO at ${p}_{\mathrm{c}}$ is confirmed. Above ${T}_{\mathrm{N}}(p)$ and beyond ${p}_{\mathrm{c}}$, an additional crossover scale ${T}^{*}(p)$ characterizes the change from pure to stretched exponential relaxation in zero field. Remarkably, ${T}^{*}(p)$ agrees with previously determined signatures of entropy accumulation above LRO. This coincidence microscopically evidences fluctuating frustrated spins at $T\ensuremath{\le}{T}^{*}$ with spin-liquid behavior. Power-law divergences of the temperature and longitudinal field dependences of the relaxation rate, with time-field scaling, at pressures between ${p}_{c}$ and 1.7 GPa characterize this regime as quantum critical.

Magnetic and magnetocaloric properties in GdFeTiO5 and GdMnTeO6

We report the magnetic and magnetocaloric properties of two Gd-based compounds. First, for the orthorhombic lattice compound GdFeTiO5, no signature of long-range magnetic ordering is observed down to 2 K. The maximum magnetic entropy change (−ΔSMmax) is derived to be 18.9 J kg−1 K−1 at 3 K for 0–3 T and 33.6 J kg−1 K−1at 5 K for 0–7 T, respectively, which is attributed to the rotation of spins of weakly ferromagnetically coupled Gd3+/Fe3+ ions toward the external magnetic field. Second, a new honeycomb layered tellurate GdMnTeO6 is synthesized. The compound crystallizes in a trigonal structure with space group P-31c and is long-range antiferromagnetically ordered at TN = 7.0 K. The value of −ΔSMmax at TN is about 14.8 J kg−1 K−1 for 0–3 T and 29.8 J kg−1 K−1 for 0–7 T, respectively, which is associated with field-induced antiferromagnetic to ferromagnetic transition. Thus, with the large value of −ΔSMmax and the absence of thermal and field hysteresis, both Gd compounds are candidates for low-temperature magnetocaloric materials. In relative to GdFeTiO5, the reduction of MCE in GdMnTeO6 might be associated with antiferromagnetic order.

Low-temperature magnetic crossover in the topological kagome magnet TbMn6Sn6

Magnetic topological phases of quantum matter are an emerging frontier in physics and materials science, of which kagome magnets appear as a highly promising platform. Here, we explore magnetic correlations in the recently identified topological kagome system TbMn6Sn6 using muon spin rotation, combined with local field analysis and neutron diffraction. Our studies identify an out-of-plane ferrimagnetic structure with slow magnetic fluctuations which exhibit a critical slowing down below {T}_{{{{{{{{rm{C1}}}}}}}}}^{* } ≃ 120 K and finally freeze into static patches with ideal out-of-plane order below TC1 ≃ 20 K. We further show that hydrostatic pressure of 2.1 GPa stabilises the static out-of-plane topological ferrimagnetic ground state in the whole volume of the sample. Therefore the exciting perspective arises of a magnetically-induced topological system whose magnetism can be controlled through external parameters. The present results will stimulate theoretical investigations to obtain a microscopic understanding of the relation between the low-temperature volume-wise magnetic evolution of the static c-axis ferrimagnetic patches and the topological electronic properties in TbMn6Sn6.

Prompt acceleration of a μ + beam in a toroidal wakefield driven by a shaped steep-rising-front Laguerre–Gaussian laser pulse

Recent experimental data for anomalous magnetic moments strongly indicates the existence of new physics beyond the Standard Model. Energetic μ + bunches are relevant to μ + rare decay, spin rotation, resonance and relaxation (μSR) technology, future muon colliders, and neutrino factories. In this paper, we propose prompt μ + acceleration in a nonlinear toroidal wakefield driven by a shaped steep-rising-front Laguerre–Gaussian (LG) laser pulse. An analytical model is described, which shows that a μ + beam can be focused by an electron cylinder at the centerline of a toroidal bubble and accelerated by the front part of the longitudinal wakefield. A shaped LG laser with a short rise time can push plasma electrons, generating a higher-density electron sheath at the front of the bubble, which can enhance the acceleration field. The acceleration field driven by the shaped steep-rising-front LG laser pulse is about four times greater than that driven by a normal LG laser pulse. Our simulation results show that a 300 MeV μ + bunch can be accelerated to 2 GeV and its transverse size is focused from an initial value of w 0 = 5 μm to w = 2 μm in the toroidal bubble driven by the shaped steep-rising-front LG laser pulse with a normalized amplitude of a = 22.

THE EFFECT OF VARIATION CONCENTRATION AND DEPOSITION PARAMETER TO THE OPTICAL CHARACTERISTICS AND THE CRYSTALLITE PROPERTIES OF ZINC OXIDE

The objective of the study was to obtain the ZnO thin films with variation concentration of zinc acetate dehydrate (ZAD), and variation of spin coater speed and rotation time. We observed the effect of the former parameters on the optical characteristics that comprised of the spectrum of absorption, transmittance, and ZnO crystallite size from UV-Vis spectrometer and XRD orderly. For the analysis of the effect of the variation of concentration, ZAD diluted into ethanol with the concentration 0.1M, 0.25M, 0.5M, 0.75M dan 1M, with the addition of diethanolamine (DEA). Then it was deposited above the glass substrate with spin coater, continued by the heating on the hotplate with the number of layers variation. For the analysis of deposition parameter effect on the transmittance and the size of ZnO crystal, we used 0.25M ZnO precursor solution with the addition of DEA, then deposited by speed and time of rotation of spin coater of 1230 rpm, 2500 rpm, and 3200 rpm for 10, 15 and 30 seconds of each. The smallest absorbance value 0.05 obtained for single layer 0.1M ZnO, while the maximum transmittance value obtained for three-layer 0.25M ZnO. Concentration variation did not affect the energy gap, whose value was approximately 3.2 eV for all samples. From the XRD result, we found that deposition time affected the number of diffraction lines, the size of the crystallite, and the transmittance.

Quantum Sensing and Imaging of Spin-Orbit-Torque-Driven Spin Dynamics in the Non-Collinear Antiferromagnet Mn3 Sn.

Novel non-collinear antiferromagnets with spontaneous time-reversal symmetry breaking, non-trivial band topology, and unconventional transport properties have received immense research interest over the past decade due to their rich physics and enormous promise in technological applications. One of the central focuses in this emerging field is exploring the relationship between the microscopic magnetic structure and exotic material properties. Here, nanoscale imaging of both spin-orbit-torque-induced deterministic magnetic switching and chiral spin rotation in non-collinear antiferromagnet Mn3 Sn films using nitrogen-vacancy (NV) centers are reported. Direct evidence of the off-resonance dipole-dipole coupling between the spin dynamics in Mn3 Sn and proximate NV centers is also demonstrated by NV relaxometry measurements. These results demonstrate the unique capabilities of NV centers in accessing the local information of the magnetic order and dynamics in these emergent quantum materials and suggest new opportunities for investigating the interplay between topology and magnetism in a broad range of topological magnets.

Helicity Transfer in Strong Laser Fields via the Electron Anomalous Magnetic Moment.

Electron beam longitudinal polarization during the interaction with counterpropagating circularly polarized ultraintense laser pulses is investigated, while accounting for the anomalous magnetic moment of the electron. Although it is known that the helicity transfer from the laser photons to the electron beam is suppressed in linear and nonlinear Compton scattering processes, we show that the helicity transfer nevertheless can happen via an intermediate step of the electron radiative transverse polarization, phase matched with the driving field, followed up by spin rotation into the longitudinal direction as induced by the anomalous magnetic moment of the electron. With spin-resolved QED MonteCarlo simulations, we demonstrate the consequent helicity transfer from laser photons to the electron beam with a degree up to 10%, along with an electron radial polarization up to 65% after multiple photon emissions in a femtosecond timescale. This effect is detectable with currently achievable laser facilities, evidencing the role of the leading QED vertex correction to the electron anomalous magnetic moment in the polarization dynamics in ultrastrong laser fields.

Spin-Group Symmetry in Magnetic Materials with Negligible Spin-Orbit Coupling

Symmetry formulated by group theory plays an essential role with respect to the laws of nature, from fundamental particles to condensed matter systems. Here, by combining symmetry analysis and tight-binding model calculations, we elucidate that the crystallographic symmetries of a vast number of magnetic materials with light elements, in which the neglect of relativistic spin-orbit coupling (SOC) is an appropriate approximation, are considerably larger than the conventional magnetic groups. Thus, a symmetry description that involves partially-decoupled spin and spatial rotations, dubbed as spin group, is required. Spin group permits more symmetry operations and thus more energy degeneracies that are disallowed by the magnetic groups. One consequence of the spin group is the new anti-unitary symmetries that protect SOC-free Z_2 topological phases with unprecedented surface node structures. Our work not only manifests the physical reality of materials with weak SOC, but also shed light on the understanding of all solids with and without SOC by a unified group theory.