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Journal of Physics D: Applied Physics - latest papers

Latest articles for Journal of Physics D: Applied Physics

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  • Electrical detection of interfacial exchange field at the (ferromagnetic insulator) | ...
    The spin–orbit field and interfacial exchange field (IEF) are two major interface phenomena, and the detection and manipulation of these fields can enable a variety of nanoscale spintronics devices. Optimizing the IEF, which governs the spin-dependent scattering asymmetry at (ferromagnetic insulator)|(normal metal) interfaces, will pave the way for next-generation nanoscale, low-power insulator spintronics devices. Here, we demonstrate an experimental pathway to detect an IEF between insulating ferromagnet EuS and non-magnetic Cu using magnetoresistance (MR) measurements, and show that the spin-dependent scattering at the common interface can lead to a significant current-in-plane MR in Py Cu EuS trilayer Hall-bar device. Our experiment suggests that simple magnetoresistance measurements can be used to experimentally detect the IEF and thereby the magnetic state of a ferromagnetic insulator.

  • Measurements of argon 4p state population densities in a capacitively coupled discharge
    Optical emission spectroscopy is performed in a capacitively coupled 13.56 MHz radio-frequency argon plasma discharge with a 2 cm gap between parallel plate electrodes. Cycle-averaged measurements are made at the center of the discharge volume at pressures of 0.1 Torr to 10 Torr and peak-to-peak voltages 1 kV. Spectra are calibrated for absolute spectral radiance, and populations of excited electronic states are inferred from the atomic transition lines. Measurements of all ten states comprising the Ar(4p) grouping are reported individually, and the population distributions analyzed as functions of both pressure and voltage. It is found that the population densities increase with applied voltage. The state distribution is highly non-equilibrium and the relative populations are insensitive to voltage or pressure at pressures 1 Torr. At higher pressures, the relative population distribution becomes a function of both pressure and voltage. Uncertainty quantification is performed using a Bayesian approach, making the reported population densities useful for plasma modeling purposes and validation of numerical simulations.

  • Tri-axial time-dependent magnetic field calibrated in-situ by harmonic analysis of adiabatically evolving atomic spins
    We introduce a methodology to calibrate in situ a set of coils generating bi- or tri-axial magnetic fields, at frequencies where a calibration performed under static conditions would be inaccurate. The methodology uses harmonic analysis of one component of the magnetization of an atomic sample whose spins adiabatically follow an ad hoc applied time-dependent field. The procedure enables the identification of phases and amplitudes of the coil currents required to produce a dynamic magnetic field with the assigned polarization. This determines coil constants that can be subsequently used to produce arbitrary three-dimensional time-dependent fields.

  • Reconstructing the Hall drift current by neural network
    Reconstruction of the Hall drift current (HDC) is important for monitoring the performance of a Hall thruster. One of the noninvasive reconstruction methods, which utilises an external magnetic sensor array to measure the magnetic field induced by the HDC and reconstruct the HDC according to the law of electromagnetic induction, has great application potential. In previous research, the relationship between the HDC and the measured magnetic flux densities was formulated with a linear magnetostatic model, and the HDC was reconstructed by solving a magnetostatic inverse problem using the least-squares (LS) method. However, the reconstruction results were prone to large errors. Because the regularisation term is introduced to reduce the ill-posedness of the inverse problem, subjective errors are inevitable when selecting the regularisation parameters. In this study, a method that utilises a Bayesian regularised backpropagation neural network to realise noninvasive reconstruction was developed. Compared with the traditional LS method, the proposed method overcomes the linear limitations of the magnetostatic model and avoids the subjectivity of the regularisation parameters. The results show that the reconstruction accuracy improved by more than 90%, and the recognition capability for different HDCs was significantly strengthened. This study provides strong support for the noninvasive detection of HDC and is also of great reference value for reconstruction research of other complex plasma currents.

  • Surface Brillouin light spectroscopy of high-frequency guided elastic waves in CoFeB-multilayers on lithium niobate
    CoFeB alloy is a ferromagnetic material that is often considered to produce synthetic antiferromagnets (SAF) used in spintronic devices. SAF host spin waves with high tunability, making their coupling with surface acoustic waves (SAWs) a promising avenue for next-generation communication devices. This coupling offers potential advantages such as SAW tunability and non-reciprocal operation in the multi-gigahertz range. Epitaxial lithium niobate (LN) thin films on sapphire substrates have emerged as a promising solution for achieving high SAW phase velocities. The combination of LN thin films with SAF, for instance based on CoFeB-based multilayers, hence offers new possibilities for engineering acoustic wave propagation. As the elastic properties of CoFeB depend on the composition of the alloy, their determination is a requisite to evaluate SAW dispersion. We investigate elastic wave dispersion in Co40Fe40B20-based multilayers on LN/ZX-sapphire, ZX-LN, and SiO2/Si substrates, combining surface Brillouin light spectroscopy and finite element computations. Surface-guided phonons ranging from 9 to 18 GHz are observed, for a wavelength of about 300 nm, and the elastic constants of Co40Fe40B20 are estimated from them.