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Unidirectional spin Hall magnetoresistance (USMR) is a magnetoresistance effect with potential applications to read two-terminal spin–orbit-torque (SOT) devices directly. In this work, we observed a large USMR value (up to 0.7 × 10−11 per A/cm2, 50% larger than reported values from heavy metals) in sputtered amorphous PtSn4/CoFeB bilayers. Ta/CoFeB bilayers with interfacial MgO insertion layers are deposited as control samples. The control experiments show that increasing the interfacial resistance can increase the USMR value, which is the case in PtSn4/CoFeB bilayers. The observation of a large USMR value in an amorphous spin–orbit-torque material has provided an alternative pathway for USMR application in two-terminal SOT devices.

Bulk perpendicular magnetic anisotropy materials are proposed to be a promising candidate for next-generation ultrahigh density and ultralow energy-consumption spintronic devices. In this work, we experimentally investigate the structure, thermal stability, and magnetic properties of FePd thin films seeded by a Ru layer. An fcc-phase Ru layer induces the highly-ordered L1(0)-phase FePd thin films with perpendicular magnetic anisotropy (K(u) ~ 10.1 Merg/cm(3)). The thermal stability of FePd samples is then studied through the annealing process. It is found that a K(u) ~ 6.8 Merg/cm(3) can be obtained with the annealing temperature of 500 °C. In addition, the damping constant α, an important parameter for switching current density, is determined as a function of the testing temperature. We observe that α increases from 0.006 to 0.009 for as-deposited FePd sample and from 0.006 to 0.012 for 400 °C-annealed FePd sample as the testing temperature changes from 25 °C to 150 °C. These results suggest that Ru-seeded FePd provides great potential in scaling perpendicular magnetic tunnel junctions below 10 nm for applications in ultralow energy-consumption spintronic devices.

In this work, we study the effects of mobile oxygen ions in a synthetic antiferromagnet structure gated by a sputtered SiO2 dielectric layer for memory and logic applications. Our devices utilize electrochemical reactions between dielectric reactive species and magnetic elements to create irreversible changes in magnetization. We analyzed the dependence of ion velocity on the gate dielectric properties such as the lattice parameter, oxygen migration energy barrier, and electric field (E-field). Hall bar devices were patterned and tested to determine the interlayer exchange coupling between the CoFeB and [Co/Pd]n layers. The anomalous Hall effect (AHE) of the CoFeB layer at different gate voltages (Vg) was measured to determine the Vg dependence. A sharp change in the behavior of the CoFeB layer with respect to negative Vg results in a non-reciprocal decrease in the coercivity and magnetization and an increase in exchange bias. The observed change in exchange bias field and magnetization allows us to measure the change in the effective thickness of the CoFeB layer. This led us to conclude that the source of such behavior is the negatively charged mobile oxygen ions from the SiO2 gate.

Bulk perpendicular magnetic anisotropy materials are proposed to be a promising candidate for next-generation ultrahigh density and ultralow energy-consumption spintronic devices. In this work, we experimentally investigate the structure, thermal stability, and magnetic properties of FePd thin films seeded by an Ru layer. An fcc-phase Ru layer induces the highly-ordered L10-phase FePd thin films with perpendicular magnetic anisotropy (Ku ∼10.1 Merg/cm3). The thermal stability of FePd samples is then studied through the annealing process. It is found that a Ku ∼6.8 Merg/cm3 can be obtained with an annealing temperature of 500 °C. In addition, the Gilbert damping constant α, an important parameter for switching current density, is determined as a function of the testing temperature. We observe that α increases from 0.006 to 0.009 for the as-deposited FePd sample and from 0.006 to 0.012 for the 400 °C-annealed FePd sample as the testing temperature changes from 25 °C to 150 °C. These results suggest that Ru-seeded FePd provides great potential in scaling perpendicular magnetic tunnel junctions below 10 nm for applications in ultralow energy-consumption spintronic devices.

Magnetic storage and magnetic memory have recently shifted towards the use of magnetic thin films with large perpendicular magnetic anisotropy (PMA) to simultaneously satisfy the requirements in storage density and thermal stability. Understanding the magnetic switching process and its dependence on the Gilbert damping (α) of materials with large PMA is crucial for developing low-power consumption, fast-switching, and high-thermal stability devices. The need to quantify α of materials with large PMA has resulted in the development of the all-optical ultrafast Time-Resolved Magneto-optical Kerr Effect (TR-MOKE) technique. While TR-MOKE has demonstrated its capability of capturing magnetization dynamics of materials with large PMA, a quantitative analysis regarding the operational optimization of this emerging technique is still lacking. In this paper, we discuss the dependence of the TR-MOKE signal on the magnitude and angle of the applied field, by utilizing a numerical algorithm based on the Landau-Lifshitz-Gilbert equation. The optimized operational conditions that produce the largest TR-MOKE signals are predicted. As an experimental verification, we conduct TR-MOKE measurements on a representative sample of a tungsten-seeded CoFeB PMA thin film to show the excellent agreement of the model prediction with measurements. Our analysis results in a better understanding of the external field influence on the magnetization precession processes. The results of this work can also provide guidance on selecting operational conditions of the TR-MOKE technique to achieve optimal signal-to-noise ratios and thus more accurate measurements of magnetization dynamics.

We propose a method for generating an elliptic perfect vector beam (EPVB) by modulating the dynamic and geometric phases. It is theoretically demonstrated that the shape of the beam can be changed from circle to ellipse by setting the scale factor m of the dynamic phase, but the diameter of it is independent on the topological charge and the polarization order. Since the geometric phases provided by the dialectic Q-plate vary with the polarization state of the illumination beam, EPVB can be converted to the elliptic perfect optical vortex (EPOV) beam by changing the polarization state of the illuminating beam. Therefore, we also provide an alternative method to generate the EPOV beam. The experimental results agree well with the theoretical expectations.

Fe4N thin films with (001) texture were prepared by reactive sputtering on MgO substrates, utilizing either a Cr or Ag buffer layer to facilitate the epitaxial growth. X-ray diffraction, atomic force microscopy, and vibrating sample magnetometry measurements show that the Fe4N thin film grown on the Ag buffer layer is superior to that grown on the Cr buffer layer. The point contact Andreev reflection measurement was then conducted, and the spin polarizations were determined to be 61.1% and 81.3% for Fe4N thin films with Cr and Ag buffer layers, respectively. The 81.3% spin polarization is significantly higher than the ratio reported previously for Fe4N and is comparable with that of state-of-the-art Heusler alloys. This result is in agreement with the theoretical prediction on the discrepancy between the two differently defined spin polarizations for Fe4N. Moreover, our study indicates that an optimized growth process for Fe4N thin films is crucial for achieving a high spin polarization and that true half-metallicity could potentially be realized with Fe4N. The high spin polarization of Fe4N combined with its low fabrication temperature and simple composition makes Fe4N a competitive candidate to be a half-metallic ferromagnet in spintronic devices.

We studied the tunnel magnetoresistance (TMR) of L10-FePd perpendicular magnetic tunnel junctions (p-MTJs) with an FePd free layer and an inserted diffusion barrier. The diffusion barriers studied here (Ta and W) were shown to enhance the TMR ratio of the p-MTJs formed using high-temperature annealing, which are necessary for the formation of high quality L10-FePd films and MgO barriers. The L10-FePd p-MTJ stack was developed with an FePd free layer with a stack of FePd/X/Co20Fe60B20, where X is the diffusion barrier, and patterned into micron-sized MTJ pillars. The addition of the diffusion barrier was found to greatly enhance the magneto-transport behavior of the L10-FePd p-MTJ pillars such that those without a diffusion barrier exhibited negligible TMR ratios (

Spin-orbit torque (SOT) induced magnetization switching has become a research focus in spintronics because it enables energy-efficient switching. There have been several experiments realizing field-free SOT-induced magnetization switching of materials with perpendicular magnetic anisotropy (PMA) in a bilayer system, either using thin Co(Fe) and CoFeB layers with interfacial PMA or using Co/Ni multilayers. All of these stacks are ferromagnets with large saturation magnetization (MS). Here, we demonstrate SOT switching in a multilayer stack of CoFeB/Gd/CoFeB. This stack shows a good PMA and a low MS (370 ± 20 emu/cm3), where CoFeB and Gd layers are antiferromagnetically exchange-coupled with each other. SOT induced magnetization switching has been demonstrated in this stack at zero magnetic field with a switching current density of ∼9.6 × 106 A/cm2 by using antiferromagnetic PtMn as the spin Hall channel material. The spin Hall angle of PtMn was also determined to be ∼0.084 ± 0.005 by performing a second harmonic Hall measurement. This layer structure is compatible with perpendicular magnetic tunnel junctions (p-MTJs), which could enable field-free three-terminal p-MTJs and lead to memory and logic devices based on SOT.

Reflective gradient metasurfaces are reported as flat, ultra-thin light focusers using a cross-resonator array with spatially varied geometric parameters atop a continuous gold ground plane spaced by a layer of SiO2. The sub-wavelength cross-shaped building element offers polarization-independent performance and full 2π phase tuning range by varying its width and length, which is explained by an analytical model based on harmonically oscillating dipole antenna. With a radial phase gradient, a metasurface is demonstrated to function as a parabolic reflector at 1.47 μm wavelength with the measured efficiency of 44%. In addition, by elaborately engineering the planar distribution of different building elements, another two focusing reflectors are designed and experimentally verified to anomalously reflect and concentrate light along normal direction but with oblique incident angles of 30° and 60°, respectively.

We demonstrate that recent data on the length and temperature dependence of the critical current in Josephson junctions with YBa2Cu3O7−x electrodes coupled by Ca‐ and Co‐substituted YBa2Cu3O7−x interlayers are consistent with the conventional theory of the proximity effect.

We describe the fabrication and properties of Nb‐AlOx‐Nb Josephson tunnel junctions having critical current densities as high as 400 kA/cm2, roughly an order of magnitude larger than any previously reported for this materials system. The quality of the junction characteristics, as indicated by the current level at subgap voltages, is considerably lower in high‐Jc than in low‐Jc junctions. However, over the entire high‐Jc range of 20–400 kA/cm2, the quality of our junctions remains the same (i.e., subgap current scales with critical current).