The antiferromagnet (AFM) and ferromagnet (FM) interface is a unique branch of magnetics of broad scientific interest. AFMs play an important role in spin‐orbit torque devices based on their ability ...to generate spin‐polarized current and exchange bias when combined with FMs. In this study, an interesting spin‐orbit torque (SOT) ratchet involving the exchange spring effect in an IrMn/CoFeB bilayer device with perpendicular anisotropy and exchange bias is developed. The combined use of electrical and spectroscopic analysis reveals that the exchange spring in IrMn/CoFeB bilayer yields unidirectional anisotropy, resulting in a collinear/orthogonal AFM/FM spin configuration at the interface upon switching CoFeB magnetization upward/downward. The ratcheting characteristics resulting from unidirectional anisotropy manifest in SOT switching. In this process, magnetization against the exchange spring features digital‐like switching with a sharp transition, whereas the reverse function is characteristic of analog switching with a gradual transition tail. The dual digital‐analog characteristics of the IrMn/CoFeB bilayer may be of benefit in neuromorphic and memory applications.
A spin‐orbit torque ratchet is discovered in an anti‐ferromagnet (IrMn)/ferromagnet (CoFeB) bilayer device with exchange bias. An exchange spring effect is found to be responsible for the unidirectional anisotropy of CoFeB, which supports the multilevel cell feature for neuromorphic applications. This finding opens a new avenue for the advanced spin‐orbit torque (SOT) technology.
The stability and activity of Platinum catalysts under the redox process are the key parameters affecting catalytic performance. Here, we investigated the surface species evolution of low‐loading Pt ...catalyst deposited on a Nafion membrane through e‐beam deposition during redox reactions by using in situ X‐ray photoelectron spectroscopy (XPS) combined with a static electrochemical cell. Operando ambient‐pressure XPS measurement revealed the oxide species (Ptδ+, Pt2+, and Pt4+) evolution over different potentials in the water layer constructed by an acid solution. The amount of Pt2+ increased with an increment of the anodic potential, whereas Pt4+ suddenly formed when the threshold voltage of the oxygen evolution reaction was crossed. Hysteresis of Pt2+ was revealed as Pt4+ was completely reduced when returning to the open circuit potential. Incorporating depth‐profiling studies enabled us to uncover the mechanism of oxide species evolution between the surface and subsurface of the Pt catalyst during a redox reaction.
The surface species evolution on membrane electrode with low‐loading Platinum catalyst is investigated by operando ambient‐pressure X‐ray photoelectron spectroscopy. The results provide a better understanding of the interaction between the conductive metallic Pt catalyst and hydrophilic oxide overlayer for oxygen evolution reaction.
Dry eye disease (DED) has become a common eye disease in recent years and appears to be influenced by environmental factors. This study aimed to examine the association between the first occurrence ...of DED, air pollution and weather changes in Taiwan. We used the systematic sampling cohort database containing 1,000,000 insureds of the National Health Insurance of Taiwan from 2004 to 2013, and identified a total of 25,818 eligible DED subjects. Environmental data, including those of air pollutants, temperature and relative humidity, were retrieved from the environmental monitoring stations adjacent to subjects' locations of clinics as exposure information. We applied the case-crossover design, which used the same subjects experiencing exposures on diagnosis days as cases and those on other days as controls. The descriptive statistics showed that the first occurrences of DED were the most for the elderly by age (53.6%), women by gender (68.9%), and spring by season (25.9%). Multivariate conditional logistic regression analyses indicated that carbon monoxide (CO), nitrogen dioxide (NO₂), and temperature were positively associated with DED (
< 0.05), while relative humidity was negatively related (
< 0.001). Because CO and NO₂ together are considered a surrogate of traffic emission, which is easier to control than the uprising temperature, it is suggested that efficient management and control of traffic emission may lower the probability of DED occurrence.
•Fabrication BiSe-based SOT devices with ultra-thin insertion layers of Pt, Cu and Ta.•Investigating the role of these insertion layers on the SOT performance.•Quantifying the SOT performance using ...X-ray and transport measurements.
The way inter-mixing chemical state influences the damping-torque efficiency of a spin–orbit torque (SOT) heterostructure is a matter of debate. This is because it acts as a local symmetry-breaking that differs from the global symmetry-breaking at the interface. A combination of angle-resolved X-ray photoelectron spectroscopy (AR-XPS), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) was utilized to investigate the composition-gradient effects on the damping-torque efficiency of the Bi2Se3/insertion (Ta, Pt, Cu)/CoFeB SOT devices, with the insertion to be 0.5 and 1.0 nm. These embedded metals have the advantages of (i) Ta: suppressing CoFeB magnetic dead-layer (ii) Pt: large spin-hall angle (iii) Cu: larger spin-diffusion length. From AR-XPS we observed a sharper composition gradient for Pt-0.5 nm than Pt-1.0 nm in terms of the Se-Pt state. By XAS branching ratio and XMCD sum-rule analyses, we obtained larger spin–orbit coupling (SOC) and spin-polarization (SP) effects on the Pt-0.5, Pt-1.0 nm samples than Cu & Ta insertion. The sharper composition gradient and promoted SOC and SP validate the larger damping-torque efficiency in the Pt-0.5 nm than the Pt-1.0 nm sample. This work manifests interfacial engineering as a powerful avenue for modulating SOT efficiency in spintronic-based applications.
This paper outlines an approach to biological sensing involving the use of spintronic devices to sense magnetic particles attached to biological carriers. We developed an enzyme-linked immunosorbent ...assay (ELISA)-based Anomalous Hall Effect magnetic sensor via surface functionalization using Triethoxysilylundecanal (TESUD). The proposed sensor uses a CoFeB/MgO heterostructure with a perpendicular magnetic anisotropy. Through several sets of magnetic layer thickness, this work also explored the optimization process of ferromagnetic layer used. Our spintronics-based biosensor is compatible with semiconductor fabrication technology and can be effectively miniaturized to integrate with semiconductor chips, which has the advantage of reduced manufacturing cost and reduced power consumption. The proposed sensor provides real-time measurement results and it is competitive to conventional biological colorimetric measurement systems in terms of accuracy and immediacy.
Display omitted
•We demonstrate the importance of considering the influence of oxygen vacancy in ferroelectric capacitors.•In-situ synchrotron X-ray techniques were used to examine the polarization ...wake-up effect of HZO.•Oxygen vacancy creates a trade-off between polarization wake-up enhancement and interfacial trap states.
TiN/Hf0.5Zr0.5O2 (HZO) is a popular heterostructure for HZO-based ferroelectric devices. In this study, in-situ synchrotron X-ray techniques were used to examine the ferroelectric wake-up effect of HZO in relation to TiN electrodes. TiN was shown to favor orthorhombic (O)/ferroelectric phase of HZO, while promoting the reconstruction of the TiN/HZO interface through the formation of oxygen vacancy (VO′′) states. Real-time changes in polarization under an applied voltage (electrical stress) indicated that VO′′ regulates the observed ferroelectric wake-up effects. The changes observed using in-situ X-ray analysis included an intensification of the VO′′ signal and the breaking of Hf-O bonds under electrical stress over a period of 1000 s. Stress-driven VO′′ increased polarization without degrading the interface, as indicated by the capacitance–voltage (C-V) characteristics of the device. It appears that VO′′ woke up HZO polarization without introducing any structural transitions. Despite the fact that VO′′ formed concomitantly with the O-phase following TiN capping, it appears that VO′′ plays an independent role in regulating polarization under an applied electrical field. Thus, VO′′ creates a trade-off between polarization wake-up enhancement and trap states. Furthermore, the results of cyclic polarization-voltage (P-V) measurement show that stress-induced VO′′ near the TiN/HZO interface is conducive to enhancing the ferroelectricity with fewer wake-up operation cycles.
In this work perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films is achieved using rapid thermal annealing under N2/H2 gas flow in ...Si/β-Ta(6.5 nm)/CFA(0.6–2 nm)/MgO(1.15 nm)/Pd(1 nm) heterostructures. The Al interdiffusion into MgO layer plays an important role in determining perpendicular magnetic anisotropy(PMA) and increasing the damping constant (α) of ultrathin CFA samples. The time of flight SIMS depth profiling along with XPS is used to study interdiffusion of Al across CFA/MgO interface. XPS analysis of Al-2p and Mg-1s spectra indicate the formation of Al2O3 and MgAl2Ox oxide phases at CFA/MgO interface in addition to pure Al metal. The Slonczewski-like and the field-like SOT effective fields are quantified using second harmonics measurements. An effective spin hall angle of β-Ta (6.5 nm) is estimated in range −0.02 to −0.06 for CFA layer thickness varied from 0.8 nm to 1.5 nm.
Ambient pressure XPS is a powerful technique capable of performing measurements with samples kept at mbar pressure. The filled gas, also X‐ray ionized, provides electrons to neutralize positive ...charges built up on insulating samples. However, this convenient neutralization scheme does not solve the charging problem completely. In this study, the effectiveness of how the electrons generated from conducting mechanical parts mounted in the immediate front of insulating samples neutralize positive charges on the samples during XPS measurements is tested. The mechanical parts range from fine gold mesh, holey carbon film to graphene monolayer, and measured insulating samples are polished sapphire and rough pellets of CaCO3 powder. All these mechanical add‐ons reduce the charging to different degrees at the expense of sample signal. Amazingly, the graphene monolayer is found to effect perfect charge neutralization for both smooth sapphire and rough CaCO3 pellet, evidenced by realistic spectral profile and binding energy values. The finding that an untreated CaCO3 pellet is often terminated with Ca(OH)(HCO3) is consistent with earlier reports. It is speculated that a likely conformal covering with graphene on the sample with rough morphology holds the key to its superb performance in charge compensation.
Charging‐free X‐ray photoelectron spectra can be routinely acquired from graphene‐covered insulating samples as the graphene acts as a self‐regulating electron source. This simple scheme works on smooth surfaces as well as topographical materials because of the conformal covering nature of graphene.
Defect engineering is of great interest to the two-dimensional (2D) materials community. If nonmagnetic transition-metal dichalcogenides can possess room-temperature ferromagnetism (RTFM) induced by ...defects, then they will be ideal for application as spintronic materials and also for studying the relation between electronic and magnetic properties of quantum-confined structures. Thus, in this work, we aimed to study gamma-ray irradiation effects on MoS2, which is diamagnetic in nature. We found that gamma-ray exposure up to 9 kGy on few-layered (3.5 nm) MoS2 films induces an ultrahigh saturation magnetization of around 610 emu/cm3 at RT, whereas no significant changes were observed in the structure and magnetism of bulk MoS2 (40 nm) films even after gamma-ray irradiation. The RTFM in a few-layered gamma-ray irradiated sample is most likely due to the bound magnetic polaron created by the spin interaction of Mo 4d ions with trapped electrons present at sulfur vacancies. In addition, density functional theory (DFT) calculations suggest that the defect containing one Mo and two S vacancies is the dominant defect inducing the RTFM in MoS2. These DFT results are consistent with Raman, X-ray photoelectron spectroscopy, and ESR spectroscopy results, and they confirm the breakage of Mo and S bonds and the existence of vacancies after gamma-ray irradiation. Overall, this study suggests that the occurrence of magnetism in gamma-ray irradiated MoS2 few-layered films could be attributed to the synergistic effects of magnetic moments arising from the existence of both Mo and S vacancies as well as lattice distortion of the MoS2 structure.
Abstract
The further commercialization of spintronic memory devices depends on the development of methods by which to assess performance. This paper presents an approach to the atomistic ...investigation of switching performance in spin transfer torque magneto-resistive random access memory (MRAM) devices with the use of interface imperfection model. Switching simulation in the nanosecond regime was made possible under this model, and we first time demonstrate that switching time is inversely proportional to interface imperfection (i.e. roughness). In investigating the damping of CoFeB/MgO films, we analyzed the effective damping constant
α
eff
, which cannot be accurately predicted for ferromagnetic layers of less than 2 nm using existing micromagnetic models. The proposed model includes a roughness parameter, which has nearly no effect on the effective damping constant in films of >2 nm, but a profound effect in films of <2 nm, reaching a 27% decrease in a 1.0 nm CoFeB film. Our finding is supported by the experimental data of classic references. We expect that these results will prove valuable in magnetic simulation and research on MRAM with ultrathin films.
PDF
