Domain structure in magnetic dots prepared by nanoimprint and e-beam lithography

The magnetic domain structure of the surface of microwires with composition Fe73.9B13.2Si10.9C2 was studied by magnetic force microscopy. It has been found that the removal of glass shell by chipping leads to distortion of the original magnetic domain structure. Chemical etching of the glass shell makes it possible to observe the magnetic domain structure due to the stresses that have arisen due to the microwire production. In the absence of an applied magnetic field, a magnetic domain structure of the surface layer is observed, consisting of domain layers inclined to the microwire axis by 45 or 135 degrees. This structure has a shape close to a zigzag. The thickness of the domain layers is not constant and varies from 3 to 5 μm. It has been found that the application of a constant magnetic field along the microwire axis causes the formation of ring domain layers of various thicknesses (from 1 to 5 μm) with different orientations of the magnetic moment relative to the microwire surface. In a field of 60 oersteds along the axis of the microwire, the domain magnetic structure consists of only ring layers of domains. Magnetic field inversion leads to almost complete inversion of the observed domain structure. In this case, the complete removal of the magnetic field leads to the formation of a new domain structure of the surface layer. Such a structure is close in shape and position of the domains to the original one, but does not repeat it.

The magneto-impedance (MI) effect attracts an increasing interest due to its high value in comparison to magnetic resistance (MR) effects, opening possible applications as e.g., high-sensitivity magnetic field detectors, magnetic recording heads, etc. However, for most samples employed in MI measurements in the literature, i.e., amorphous wires, magnetic multilayers and ribbons, the real three-dimensional domain structure remains unknown. In order to find the relation between the magnetic domain structure and the respective value of the MI effect, permalloy (Ni81Fe19) nanowires and thin films were produced by electron-beam lithography (EBL), lift-off technique and focused ion beam (FIB) milling. Wires and other structures (rectangles, circles), and domain pinning sites (notches) were manufactured with optimized dimension (size, thickness, etc.). The magnetic structure of our samples and the MI effects were analyzed by magnetic force microscopy and transport measurements.

Low cost, rapid fabrication of durable molds of grating arrays for nanoimprint lithography

The magnetic domain structure is an important factor in discussing the coercivity development mechanism. We have researched on the new observation method of magnetic domain structures using multiple distances observation of magnetic force microscope (MFM) and image processing. We observed magnetic domain structures in thermally demagnetized state and alternating current (ac) demagnetized state of ferrite-sintered magnets using this method. In addition, the initial magnetization curve was measured in each demagnetized state. There were differences in the domain structures and the initial magnetization curves in each demagnetized state. These differences suggest that irreversible multi-domain gains (IRMDGs) confirmed in rare-earth magnets are present even in sintered ferrite magnets.

Magnetic domain structures and stray fields of individual elongated magnetite grains revealed by magnetic force microscopy (MFM)

Thickness dependence of magnetic domains of MnAs films

The magnetic domain structure in thin ferromagnetic films with perpendicular anisotropy is investigated. The effect of an in-plane magnetic field on the presence of domains and the magnetization profile is analyzed within the framework of a one-dimensional analytical model. The general results are reported in a state diagram as a function of the two relevant dimensionless parameters: the quality factor and the ratio of the film thickness to the exchange length. The experimental results, including hysteresis measurements, magnetic force microscopy, and x-ray resonant magnetic scattering obtained on a generic FePd thin layer, are reported and compared to the model.

The domain structure of (PtCoPt)/Si multilayers in the dc demagnetized state has been investigated by magnetic force microscopy.The domain structure is found to change dramatically as the thickness of the non-magnetic Si sublayer (tsi) increases.Together with the analysis of magnetic properties,the variation of the domain period indicates that the domain wall energy decreases.Using the model developed by Draaisma and de Jonge,the domain wall energy is obtained.

Wave transmission media created by a periodically modulated magnetic material are referred to as magnonic crystals [1]. The dynamics of magnonic crystals are described by common concepts of solid state physics, i.e., group velocity, density of states, and band structure. We investigate so-called magnonic vortex crystals created via rectangular arrangements of magnetic vortices. Here we aim at the control of vortex-core polarizations by perpendicularly aligned bias fields and use magnetic force microscopy and broadband-ferromagnetic transmission spectroscopy. In the first step, arrays of CoPt-multilayer disks arranged in a checkerboard pattern are prepared by electron-beam lithography, sputter deposition, and lift-off processing, compare figure 1(a). Two layer types A (Pt/0.7 nm Co/Pt) and B (Pt/2x(0.8 Co/1.1 nm Pt)/Pt) of the pattern differ in the magnetic anisotropy and thus yield different switching fields of the perpendicularly magnetized disks [2]. The switching fields are investigated by Kerr microscopy. After saturation in negative field direction, disks of type B start to switch at a field strength of μ 0 H = +29 mT visible in the hysteresis loop shown in figure 1(b). The switching is completed at +37 mT where the greyscale intensity stays constant. A stable state of antiparallel magnetization of both types of disks persists up to +56 mT, where disks of type A start to switch. At +68 mT the magnetizations of disks of type A and B are aligned parallel with the positive field direction, compare figure 1(c). The switching of the multilayer disks follows a normal distribution and shows no dependence on the interdisk distance. In the next step, permalloy disks are prepared on top of the CoPt disks by electron-beam lithography, thermal evaporation, and lift-off processing. A thin Si interlayer is used to avoid direct contact of the perpendicularly and in-plane magnetized ferromagnets. The magnetization of the CoPt disks is adjusted using a perpendicularly aligned magnetic field. Subsequently an in-plane field is used to nucleate vortices in the permalloy disks. It is expected that due to stray field coupling the polarization of the vortex core in each permalloy disk is determined by the subjacent CoPt disk and coincides with the direction of the magnetization of the CoPt disk. The vortex-core polarizations are investigated using magnetic force microscopy (not shown).

Nanoimprint lithography (NIL) technology has aroused great interests in both academia and industry due to its high resolution, low-cost, and high-volume nanopatterning capability. And as an expoxy resin-based negative amplified photoresist, SU-8 is an ideal candidate for NIL because of its low-glass-transition temperature, low-volume shrinkage coefficient, and good optical properties. In this reviewing paper, we highlight the major technical achievements in NIL on epoxy resin and its applications for bio- and nanophotonic structures. NIL was also applied for the duplication of imprint templates, originally fabricated by e-beam lithography (EBL) followed by reactive ion etch (RIE), using a SU-8/ SiO 2/PMMA tri-layer technique. And nanoimprint properties were systematically investigated for optimization. The developed nanoimprint process for different applications indicates promising industrial potentials in the next generation lithography resolution.

Fe-based amorphous and nanocrystalline alloys are considered as the preferred dual-green energy-saving materials due to their unique magnetic properties, such as high permeability, low coercivity, and near-zero saturation magnetostriction. As such, they have received extensive attention in applications like magnetic core material for high-frequency transformers, common model chokes, ground fault interrupters, and rotors in motors, over the past decades. In this work, Fe<sub>64.8</sub>Co<sub>7.2</sub>Nb<sub>4</sub>Si<sub>4.8</sub>B<sub>19.2</sub> (in atom percent) amorphous alloy ribbons are prepared by using the single roller quenching method, then subsequently subjected to multi-field coupling heating treatment in the air which includes heating by Joule heating effect and tensile stress field. Furthermore, the longitudinally driven giant magneto-impedance effect and magnetic domain structures of ribbons are observed by using 4294A impedance analyzer and magnetic force microscopy, respectively. The magneto-crystalline anisotropy field and stress anisotropy field of ribbons are analyzed by using X-ray diffraction, random anisotropy model, and numerical fitting. Meanwhile, the concept of magnetic anisotropy competing factor (<i>k</i>) is proposed, from the viewpoint of magnetic anisotropy, a mechanism for regulating giant magneto-impedance effect of ribbons prepared with multi-field coupling is studied. It is found that the longitudinally driven giant magneto-impedance effect gradually transforms from the single peak to dome-like with tensile stress increasing. However, a spike and dome-like giant magneto-impedance effect appears during such transformation, which is composed of two parts: spike-like top and dome-like base. Based on the magnetic domain structure of ribbons, it is found that the typical stress-annealed transversal magnetic domain structure is observed in ribbons of <inline-formula><tex-math id="Z-20221115160531">\begin{document}$k \leqslant 0.147$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221376_Z-20221115160531.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="23-20221376_Z-20221115160531.png"/></alternatives></inline-formula>, while nucleation and splitting phenomenon of new domains are observed at the transversal magnetic domain wall in ribbons of <i>k</i> > 0.147. Both longitudinally driven giant magneto-impedance effect and domain structures provide evidence to support the competing inhibition effect of magnetic anisotropy which exists in Fe-based alloy ribbon. Therefore, it is suggested that Fe-based alloys exhibit excellent stress-sensitive properties that can be understood by the competing inhibition effects of magnetic anisotropy. It is further shown that the competing inhibition effect of magnetic anisotropy is the main reason for regulating the giant magneto-impedance effect of soft magnetic materials. This multi-field coupling Fe-based alloy has good application prospects in regulating magnetic properties of magnetic materials.

Summary form only given. Nanoscale metal-semiconductor-metal (MSM) photodetectors and MESFETs are key elements in ultra-fast optical and wireless communication systems. However, devices with sub-0.25 /spl mu/m feature sizes are typically fabricated using electron-beam lithography (EEL), which has high cost and low throughput. Nanoimprint lithography (NIL), on the other hand, has both low cost and high throughput, as well as sub-l0 nm resolution. We report the fabrication of MSM photodetectors on semi-insulating (SI) GaAs using NIL, and the examination of NIL on the quality of the nanoscale Schottky contact. We found that if the imprint pressure is 600 psi or lower, nanoscale GaAs MSM photodetectors fabricated using NIL are comparable to those fabricated by conventional EEL and photolithography, indicating no degradation to the photodetector Schottky contact induced by the imprint process.

Microstructure of polycrystalline Fe ₈₂ Ga ₁₈ sample with solidification texture

Artificial pinning sites have been fabricated for the magnetic domain pinning in perpendicular anisotropy magneto-optical (MO) thin film media. The pinning sites were radial hole array made by patterning a layer of radial gold grid on the silicon nitride (SiN) coated silicon (Si) substrate using a standard electron beam lithography. Various magnetization and demagnetization procedures were performed to investigate the magnetic domain pinning behavior. A polar Kerr microscope was used in situ to monitor the magnetic wall motion and a magnetic force microscope was employed to scan the magnetic domain structures. Magnetic domains were found to be pinned inside the hole array and resembled to the geometric shape of the holes. The coercivity in the patterned MO layer is much higher than in the unpatterned MO layer. Moreover, the coercivity in the larger pinning sites area is higher than in the smaller pinning sites area.

Local evolution of magnetic domain structures in Terfenol-D under variable magnetic fields is characterized using magnetic force microscopy and the resulting magnetostrictive strains parallel and perpendicular to the applied magnetic field are simultaneously measured. It is found that both magnetic domain structure and magnetostrictive response depend upon the loading history and a substantial change in magnetic domains is observed for Terfenol-D under opposite magnetic field, resulting in notable asymmetry in magnetostrictive strain. The technique will be useful in characterizing the evolution of magnetic domains for a wide range of ferromagnetic materials under an external field.