Magnetic domain-wall creep driven by field and current in Ta/CoFeB/MgO

Creep motion of magnetic domain wall (DW), thermally activated DW dynamics under subthreshold driving forces, is a paradigm to understand the interaction between driven interfaces and applied external forces. Previous investigation has shown that DW in a metallic system interacts differently with current and magnetic field, manifesting itself as different universality classes for the creep motion. In this article, we first review the experimental determination of the universality classes for current- and field-driven DW creeps in a Ta/CoFeB/MgO wire, and then elucidate the underlying factors governing the obtained results. We show that the nature of torque arising from current in association with DW configuration determines universality class for the current-induced creep in this system. We also discuss the correlation between the field-induced DW creep characteristics and structure observed by a transmission electron microscope. The observed results are expected to provide a deeper understanding for physics of DW motion in various magnetic materials

Ways to Reduce Water Erosion on Mountainous Slope Lands

The most important problem in the highland area is the development of technologies to reduce water erosion and improve soil fertility preservation. In order to restore degraded soils of slope lands, a number of measure is undertaken, among them planting crops across the slope and rational fertilizer treatment. To reduce erosion processes, mineral fertilizers were applied depending on the steepness of slope. High sections with the steepness of 9–10∘ received ammonium sulphate in a quantity of 60 kg/ha. Lower part of the slope with the steepness of 5–7∘ received ammonia nitrate as a nitrogen fertilizer in a quantity of 80 kg/ha, while the gentle sloping part with 2–5∘ had urea-formaldehyde fertilizer incorporated under winter tillage in a quantity of 50 kg/ha. At that, stripes were formed across the slope where tall-growing perennial herbs were planted: hill mustard (Bunias orentalis L.), silphium (Silphium perfaliatum), Eastern galega (Galeqa orientalis L.), cock’s foot grass (Dakfilis qlamerata L.). The research results have shown that thanks to fertilizers, yield of crops increases by a factor of 1.5–2, while soil losses reduced from 0.042 to 0.018 t/ha

Enhanced magnon transport through an amorphous magnetic insulator

Conduction of spin currents in disordered insulating antiferromagnets has recently been at the center of scientific debate with both long-range spin transport or no spin transport at all observed experimentally. In this study, ferromagnetic resonance has been used to probe the transmission of ac spin current through thin amorphous yttrium iron garnet (YIG) layers. The spin current is found to be mediated by evanescent spin waves with a penetration length four times larger than that of previous studies of amorphous YIG, even exceeding the spin penetration length of crystalline NiO

Enhanced magnetoelectric effect in M-type hexaferrites by Co substitution into trigonal bi-pyramidal sites

The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect

Enhanced magnetoelectric effect in M-type hexaferrites by Co substitution into trigonal bi-pyramidal sites

The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect

HAADF-STEM Image Resolution Enhancement Using High-Quality Image Reconstruction Techniques: Case of the Fe3O4(111) Surface

From simple averaging to more sophisticated registration and restoration strategies, such as super-resolution (SR), there exist different computational techniques that use a series of images of the same object to generate enhanced images where noise and other distortions have been reduced. In this work, we provide qualitative and quantitative measurements of this enhancement for high-angle annular dark-field scanning transmission electron microscopy imaging. These images are compared in two ways, qualitatively through visual inspection in real and reciprocal space, and quantitatively, through the calculation of objective measurements, such as signal-to-noise ratio and atom column roundness. Results show that these techniques improve the quality of the images. In this paper, we use an SR methodology that allows us to take advantage of the information present in the image frames and to reliably facilitate the analysis of more difficult regions of interest in experimental images, such as surfaces and interfaces. By acquiring a series of cross-sectional experimental images of magnetite (Fe3O4) thin films (111), we have generated interpolated images using averaging and SR, and reconstructed the atomic structure of the very top surface layer that consists of a full monolayer of Fe, with topmost Fe atoms in tetrahedrally coordinated sites

Nano-faceted stabilization of polar-oxide thin films : The case of MgO(111) and NiO(111) surfaces

Molecular beam epitaxy growth of polar MgO(111) and NiO(111) films demonstrates that surface stabilization of the films is achieved via the formation of neutral nano-faceted surfaces. First-principles modeling of the growth of polar MgO(111) films reveals that the growth does not proceed layer-by-layer. Instead, the Mg or O layers grow up to a critical sub-monolayer coverage, beyond which the growth of the next layer becomes energetically favorable. This non-layer-by-layer growth is accompanied by complex relaxations of atoms both at the surface and in the sub-surface, and leads to the experimentally observed surface nano-faceting of MgO and NiO (111) films through formation of neutral nano-pyramids terminated by {100} facets. These facets are limited in size by an asymptotical surface energy relation to their height; with the reconstruction being much more stable than previously reported surface terminations across a wide range of growth conditions. The termination offers access to lower coordinated atoms at the intersection of the neutral {100} planes whilst also increasing the surface area of the film. The unique electronic structures of these surfaces can be utilized in catalysis, as well for forming unique heterostructures for electronic and spintronic applications

Growth and characterisation of MnSb(0 0 0 1)/InGaAs(1 1 1)A epitaxial films

MnSb layers have been grown on InxGa1-xAs(1 1 1) A virtual substrates using molecular beam epitaxy (MBE). The effects of both substrate temperature (Tsub) and Sb/Mn beam flux ratio (JSb/Mn) were investigated. The surface morphology, layer and interface structural quality, and magnetic properties have been studied for a 3 × 3 grid of Tsub and JSb/Mn values. Compared to known optimal MBE conditions for MnSb/GaAs(1 1 1) [Tsub = 415°C,JSb/Mn = 6.5], a lower substrate temperature is required for sharp interface formation when growing MnSb on In0.48Ga0.52As(1 1 1) A [Tsub = 350°C,JSb/Mn = 6.5]. At high flux ratio (JSb/Mn = 9.5) elemental Sb is readily incorporated into MnSb films. At higher substrate temperatures and lower flux ratios, (In,Ga) Sb inclusions in the MnSb are formed, as well as MnAs inclusions within the substrate. The Sb and (In,Ga) Sb inclusions are epitaxial, while MnAs inclusions are endotaxial, i.e. all have a crytallographic relationship to the substrate and epilayer. MBE optimisation towards different device structures is discussed along with results from a two-stage growth scheme

Absence of spin-mixed states in ferrimagnet Yttrium iron garnet

The spectroscopic g-factor of epitaxial thin film Yttrium Iron Garnet (YIG) has been studied using a combination of ferromagnetic resonance spectroscopy and x-ray magnetic circular dichroism. The values obtained by the two techniques are found, within experimental error, to be in agreement using Kittel's original derivation for the g-factor. For an insulating material with an entirely Fe3+ configuration, a spin mixing correction to Kittel's derivation of the spectroscopic g-factor, as recently shown by Shaw et al. [Phys. Rev. Lett. 127, 207201 (2021)] for metallic systems, is not required and demonstrates that the spin mixing parameter is small in YIG due to negligible spin-orbit coupling

Correlated electron diffraction and energy-dispersive X-ray for automated microstructure analysis

In this study the effect of merging correlated energy dispersive X-ray (EDS) spectra and electron diffraction data on unsupervised machine learning (clustering) is explored. The combination of data allows second phase coherent precipitates to be identified, that could not be determined from either the individual EDS or diffraction data alone. In order to successfully combine these two distinct data types we leveraged a data fusion method where both data sets were normalised and combined using a robust scaler followed by variance equalisation. A machine learning pipeline was implemented which performs dimensional reduction with PCA and followed by fuzzy C-means clustering, as this allows signals from overlapping regions of the microstructure to be partitioned between different clusters. User control of this partition is used to confirm a change in the stoichiometry of the embedded second phase regions