Magnetic interlayer coupling is a critical study topic for spintronic device technology because it is an essential component in designing magnetic multilayers with functionality that can be expanded ...into application areas. Particularly, the interlayer coupling between two ferromagnetic (FM) layers with different magnetic properties in the magnetic field is the specific situation to develop spintronic applications, such as increasing the sensitivity of magnetic field sensors. Therefore, the film structure was chosen as two layers in this study; the first ferromagnetic layer (FM1-CoRh) has a perpendicular and the second ferromagnetic layer (FM2-Fe) has an in-plane (IP) magnetic easy axis in the presence of a magnetic field. Here, a non-magnetic (NM) Rh spacer layer separated the two FM layers. The magnetic properties dependent on spacer layer thickness (t) in CoRh/Rh/Fe multilayers were investigated in detail. It is found that the strength of interlayer coupling alters depending on the t.
Although both theoretical predictions and experimental observations have demonstrated that the Gilbert damping is anisotropic at ferromagnet/semiconductor interface possessing robust interfacial ...spin-orbit coupling, it is not well understood whether non-local Gilbert damping driven by spin pumping in heavy metal/ferromagnetic metallic bilayers is anisotropic or not. Here, we investigated the angular and frequency dependence of magnetic relaxation in epitaxial Pd/Fe films on MgO(001) substrates. After disentangling parasitic contributions, we unambiguously observe that the non-local Gilbert damping is isotropic in the Fe(001) plane, suggesting that the spin transport across the Pd/Fe interface is independent of the Fe magnetization orientation. First principles calculations reveal that the effective spin mixing conductance of the Pd/Fe interface is nearly invariant for different magnetization directions, in good agreement with the experimental observations. These results offer valuable insight into spin transport in metallic bilayers, and facilitate the development of next-generation spintronic devices.
In the literature, a magnetic “easy” axis perpendicular to the film plane at room temperature (i.e., perpendicular magnetic anisotropy - PMA) has been reported in Ni (nickel) layers with thicknesses ...below ≈15 nm. In this work, we observed room-temperature PMA in a-Si/Ni/a-Si (where a-Si denotes amorphous silicon) thin film structures with nickel layer thicker than 15 nm. Two layered structures were prepared by DC/RF triode sputtering: a-Si/Ni/a-Si sandwich structure and a-Si/Ni/a-Si5 multilayer structure. The cross sectional STEM revealed uniform Ni layers with thicknesses of ≈17 nm in a-Si/Ni/a-Si5 – multilayer and ≈28 nm in a-Si/Ni/a-Si – single-layer whereas amorphous Si layers were ≈15 nm and 170 nm thick, respectively. An amorphous Ni–Si interphase was also observed in the layered structures. The XRD showed patterns for fcc-Ni with dominant (111) orientation. No other crystalline phases were observed in the XRD patterns. To our knowledge, there are no literature reports of easy magnetization direction perpendicular to the film plane at room temperature for Ni layers with thickness of ≈28 nm as presented in this work. The origin of PMA in a-Si/Ni/a-Si films may be mainly attributed to the magnetoelastic anisotropy whereas the secondary source of PMA is believed to be the surface anisotropy and magnetocrystalline anisotropy of 111 columnar grains. Amorphous silicon layers (substrate) do not have a well-defined lattice structure like crystalline substrates. Therefore, they do not induce strains in the nickel layers through lattice mismatch as in the case of epitaxy. The strains can be caused by other factors such as diffusion-induced strain, thermal expansion mismatch or intrinsic stresses during the growth process. These results could be important for applications in memory devices, sensors, logic chips, magneto-optic, magneto-electronic and spintronic devices and in fundamental research, as well as first step toward preparation and understanding of the PMA in thick nickel layers.
Functional neuroimaging provides means to understand the relationship between brain structure and associated functions. Functional MR (fMR) imaging can offer a unique insight into preoperative ...planning for central nervous system (CNS) neoplasms by identifying areas of the brain effected or spared by the neoplasm. BOLD (blood-oxygen-level-dependent) fMR imaging can be reliably used to map eloquent cortex presurgically and is sufficiently accurate for neurosurgical planning. In patients with brain tumors undergoing neurosurgical intervention, fMR imaging can decrease postoperative morbidity. This article discusses the applications, significance, and interpretation of BOLD fMR imaging, and its applications in presurgical planning for CNS neoplasms.
•X-ray detected ferromagnetic resonance (XFMR) is a new synchrotron-based technique.•It combines ferromagnetic resonance with X-ray magnetic circular dichroism.•The amplitude and phase response is a ...signature for spin-transfer torque coupling.•Field-dependent phase plots distinguish between static and dynamic exchange coupling.•Spin currents can be strongly enhanced in anisotropic magnetic materials.
X-ray detected ferromagnetic resonance (XFMR) has recently emerged as a powerful synchrotron-radiation-based tool able to study the element-selective magnetization dynamics. Magnetic and chemical contrast in XFMR is obtained by X-ray magnetic circular dichroism (XMCD), while the phase difference between the magnetization precessions is monitored using stroboscopic probing. A unique property of time-resolved XFMR is the visualization of the magnetization precession for each individual layer in a magnetic device. Measurement of the amplitude and phase response of the magnetic layers gives a clear signature of spin-transfer torque (STT) coupling between ferromagnetic layers due to spin pumping.
We report spin-torque ferromagnetic resonance studies of the efficiency of the damping-like (ξDL) spin–orbit torque exerted on an adjacent ferromagnet film by current flowing in epitaxial (001) and ...(110) IrO2 thin films. IrO2 possesses Dirac nodal lines (DNLs) in the band structure that are gapped by spin–orbit coupling, which could enable a very high spin Hall conductivity, σSH. We find that the (001) films do exhibit exceptionally high ξDL ranging from 0.45 at 293 K to 0.65 at 30 K, which sets the lower bounds of σSH to be 1.9 × 105 and 3.75 × 105 Ω–1 m–1, respectively, 10 times higher and of opposite sign than the theoretical prediction. Furthermore, ξDL and σSH are substantially reduced in anisotropically strained (110) films. We suggest that this high sensitivity to anisotropic strain is because of changes in contributions to σSH near the DNLs.
M-type Sr (SrM) hexaferrites have been widely applied in millimetre/microwave ferrite devices such as circulators and isolators. SrM hexaferrites must exhibit a high remanence ratio Mr/Ms, a high ...anisotropy field Ha, and a low ferromagnetic resonance (FMR) linewidth ΔH to further develop millimetre/microwave equipment and devices with high frequencies, miniaturisation, and planarisation. However, it is difficult for M-type hexaferrite to simultaneously meet the requirements of high Mr/Ms, high Ha, and low ΔH, which are key to realising high-frequency self-biased ferrite devices. In this work, Ca–La–Co-substituted SrM ferrite was prepared, and the influence of La substitution on the micromorphology, static magnetic properties, and ΔH values of SrM hexaferrites is discussed in detail. The results demonstrated that as the La substitution content x increased from 0.0 to 0.5, the saturation magnetisation 4πMs and coercivity Hc initially increased, and then decreased. The Ha values of all samples were higher than 18 kOe. The FMR linewidth ΔH initially increases, and then decreased after reaching a maximum value at x = 0.2. The independent grain approximation theory was used to analyse the changing trend of the FMR linewidth. The results showed that the crystalline anisotropy linewidth ΔHa accounted for a larger proportion of the FMR linewidth than the porosity linewidth ΔHp. The sample with a La substitution content x of 0.3, exhibited the best performance (4πMs = 3915 Gs, 4πMr = 3387 Gs, Hc = 1818 Oe, Mr/Ms = 0.865, large Ha = 23.99 kOe, and ΔH = 1548 Oe at 58.8 GHz). The materials prepared in this research have significant potential for application in high-frequency self-biased devices and microwave engineering.
PDF
