Thermomagnetic data writing and erasing in DyCo/NiFe (TbFe/NiFe) film structures

A new principle of data writing and erasing is proposed based on the exchange coupling between magnetic layers with mutually orthogonal orientations of the effective magnetization. The new method provides for a significant decrease in energy consumption. The possibility of using bilayer magnetic films of the (rare earth metal-transition metal)/NiFe type possessing unidirectional anisotropy as the media for thermomagnetic writing and erasing of magnetooptical data is studied.     

Studying the mechanism of exchange coupling in ferro/ferrimagnet NiFe/DyCo film structures

Dependence of the magnetic and magnetooptical properties of an exchange-coupled NiFe/DyCo bilayer system on the thickness (t _DyCo) of a magnetically hard layer has been studied. It is established that the unidirectional anisotropy vanishes at t _DyCo ～ 400 Å, while the coercive field in the magnetically soft layer becomes comparable to the exchange-induced field shift. In this case, the DyCo layer magnetization is almost parallel to the film plane, whereas a reference DyCo film exhibits a perpendicular anisotropy. A model of the magnetic state of layers in the ferro/ferrimagnetic layer structure under consideration is proposed, which assumes that a 180° domain wall is formed at the interface upon magnetization reversal in the magnetically soft layer.     

Peculiarities of magnetization reversal in exchange-coupled ferro/ferromagnet NiFe/CoP film structures

The effect of layer thicknesses on the magnetic properties and mechanism of magnetization reversal in exchange-coupled NiFe/CoP film structures has been studied. The process of magnetization reversal was studied by analysis of the magnetic-induction and magneto-optical hysteresis loops. It is established that, as the thicknesses of layers in the NiFe/CoP film structure are increased, the system exhibits a transition from homogeneous magnetization reversal in the structure to exchange spring formation in the soft magnetic layer.     

Broadband microwave absorption in [NiFe/FeMn]n exchange-coupled multilayer films

[NiFe/FeMn]_n exchange-coupled multilayer films have been fabricated on the silicon substrate by magnetron sputtering deposition. The static and dynamic magnetic properties of multilayer films have been investigated with varying numbers of layers. The results show that the linewidth and permeability of imaginary resonance peak are increased with increasing numbers of layers. For the NiFe/FeMn/NiFe sample, the resonance frequency shows a different shift with applying external magnetic field along the direction of easy and hard magnetization axis of the sample, respectively, indicating a different magnetic reversal process in two ferromagnetic layers. It proved that the increase of linewidth was originated from the different interface exchange coupling.     

交换耦合的纳米软-硬磁性晶粒的有效各向异性常数

以α-Fe、Nd2Fe14B为例,研究了纳米晶粒尺寸对交换耦合的软-硬磁性晶粒各向异性的影响.结果表明,软-硬磁性晶粒的有效各向异性常数〈Ksh〉随软磁性晶粒尺寸Ds的增加而减小,随硬磁性晶粒尺寸Dh的增加而增大.当Ds/Dh为固定值且1/1.1≥Ds/Dh≥1/1.4时,〈Ksh〉在Ds为10～20nm之间取得一极大值.当Dh＞25nm,Ds在10nm左右时,可获得较大的〈Ksh〉.     

Multiple film cracking in film/substrate systems with residual stresses and unidirectional loading

Multiple film cracking in film/substrate systems is analyzed in the present study. Specifically, the experimental measurements of multiple cracking of SiO _x films of various thicknesses on polyethylene terephthalate substrates are analyzed. The system is subjected to both residual stresses and unidirectional tensile loading. Considering a three- dimensional geometry, an analytical model is developed to derive the stress distribution in the system, and the film-cracking problem is analyzed using both the strength and the energy criteria. Compared to the strength criterion, the energy criterion shows better agreement with the measurements of the crack density versus applied strain relation.     

Perpendicular GMI Effect in Meander NiFe and NiFe/Cu/NiFe Film

We have evaluated the perpendicular giant magnetoimpedance effect (GMI) in both NiFe and NiFe/Cu/NiFe films with meander geometry in the $>$1 MHz high-frequency range. With the magnetic field, the perpendicular GMI effect shows an intense GMI peak value at a certain field. This effect is comparable to the longitudinal GMI effect in both profile and peak value amplitude. The experimental results correspond well with the predictions of a single-domain rotational magnetization model. These findings demonstrate that the deflection of the anisotropy to a perpendicular direction plays an important role in the perpendicular GMI effect.      

Terahertz unidirectional invisibility in grating-based structures

A grating-based structure is proposed to realize unidirectional invisibility in the terahertz range. We show that the strict demand on refractive index for unidirectional invisibility can be flexibly satisfied in such proposed structure due to the tunable effective refractive index property of the grating layer by adjusting its geometric parameters. All these behaviours are demonstrated in the example of GaAs grating-based structure illuminated around 40 μm. Our results may lead to the development of a variety of novel terahertz devices for photonic integrated circuits.     

NiO/FeCo磁性多层膜的高频磁性

制备了一系列具有铁磁/反铁磁交换偏置作用的[NiO/Fe65Co35]10多层膜,使用振动样品磁强计(VSM)测量了样品的静磁参数,利用微带线法测量了样品4GHz-10GHz的磁谱,首次制备并测得了自然共振频率(fr)在6GHz以上,最高到fr=9.6GHz的薄膜样品。结果表明交换偏置场(Hex)、各向异性场(Hua)、以及矫顽力(Hc)随铁磁层厚度(tFM)增大而减小;基于Landau-Lifishitz(L-L)方程对静磁参量和磁谱进行了比较,发现样品自然共振频率较L-L方程计算值偏大30%以上。     

Specific features of three-dimensional wave regimes development in a vertically falling liquid film

This Letter presents the results of an experimental study of the wave regimes of the liquid film flow over the vertical plate within a range of moderate Reynolds numbers using liquids with different physical properties. The analysis of statistical characteristics of wave fields has made it possible to elaborate the classification of three-dimensional wave regimes in a range of liquid flow rates under study. Steady-state threedimensional wave regimes are shown to occur at Reynolds numbers that are significantly higher than the Reynolds number of a transition from a two-dimensional to three-dimensional wave flow.     

Specific features of proton interaction with transistor structures having a 2D AlGaN/GaN channel

It has been shown that the interaction of 1 MeV protons at doses of (0.5–2) × 10¹⁴ cm^–2 with transistor structures having a 2D AlGaN/GaN channel (AlGaN/GaN HEMTs) is accompanied not only by the generation of point defects, but also by the formation of local regions with a disordered nanomaterial. The degree of disorder of the nanomaterial was evaluated by multifractal analysis methods. An increase in the degree of disorder of the nanomaterial, manifested the most clearly at a proton dose of 2 × 10¹⁴ cm^–2, leads to several-fold changes in the mobility and electron density in the 2D channel of HEMT structures. In this case, the transistors show a decrease in the source–drain current and an order-of-magnitude increase in the gate leakage current. In HEMT structures having an enhanced disorder of the nanomaterial prior to exposure to protons, proton irradiation results in suppression of the 2D conductivity in the channel and failure of the transistors, even at a dose of 1 × 10¹⁴ cm^–2.     

Correlation between isotropic ferromagnetic resonance field shift and rotatable anisotropy in polycrystalline NiFe/FeMn bilayers

Polycrystalline NiFe/FeMn bilayers were fabricated by DC magnetron sputtering and studied by ferromagnetic resonance and vibrating sample magnetometer. The isotropic resonance field shift and the rotatable anisotropy are correlated to each other because they both undergo the maximal values around 2.5 nm and then decrease with increasing the antiferromagnetic layer thickness. These results can be explained in terms of thermally activated transition of antiferromagnetic spins.     

Directional alignment of FeCo crystallites in Si/NiFe/Ru/FeCoB multilayer with high anisotropy field above 500 Oe

In-plane magnetic anisotropy and crystal structure of FeCoB layer on Si/NiFe/Ru underlayer were investigated by using X-Ray Diffraction (XRD) measurement. A pole-figure measurement of XRD showed directionally tilted alignment of FeCo crystallites in Si/NiFe/Ru/FeCoB multilayered film with high in-plane anisotropy field H(k) but no directional alignment was found in FeCoB single layered film. The higher H(k) appeared in the Si/NiFe/Ru/FeCoB multilayered configuration with the thicker FeCoB layer. Since Ru crystallites in a multiunderlayer configuration exhibited no directional alignment, the surface structure of underlayer should be no main reason for the directional alignment of FeCo crystallites deposited on it. The dependence of hickness of FeCoB layer in Si/NiFe/Ru/FeCoB film on H(k) indicated that the in-plane magnetic anisotropy is caused by not only the structure of Ru underlayer but also oblique incidence effect of sputtered particles, which is attained in configuration of Facing Targets Sputtering (FTS) system. From these experimental results, remarkably high H(k) of 540 Oe was obtained.     

Spin valve effect of NiFe/graphene/NiFe junctions

When spins are injected through graphene layers from a transition metal ferromagnet, high spin polarization can be achieved. When detected by another ferromagnet, the spin-polarized current makes high- and low-resistance states in a ferromagnet/graphene/ferromagnet junction. Here, we report manifest spin valve effects from room temperature to 10 K in junctions comprising NiFe electrodes and an interlayer made of double-layer or single-layer graphene grown by chemical vapor deposition. We have found that the spin valve effect is stronger with double-layer graphene than with single-layer graphene. The ratio of relative magnetoresistance increases from 0.09% at room temperature to 0.14% at 10 K for single-layer graphene and from 0.27% at room temperature to 0.48% at 10 K for double-layer graphene. The spin valve effect is perceived to retain the spin-polarized transport in the vertical direction and the hysteretic nature of magnetoresistance provides the basic functionality of a memory device. We have also found that the junction resistance decreases monotonically as temperature is lowered and the current-voltage characteristics show linear behaviour. These results revealed that a graphene interlayer works not as a tunnel barrier but rather as a conducting thin film between two NiFe electrodes.      

Magnetic anisotropy of the ultrathin Fe layers in Fe/NiFe/Fe/Cu multilayers and their effect to the magnetoresistance

The effects of the deposition of ultrathin ⁵⁷Fe layers on both sides of the NiFe layers in NiFe/Cu multilayers were investigated by focusing on their structural, magnetic and magnetoresistance properties. Conversion electron Mössbauer spectroscopy measurements showed an out-of-plane magnetic anisotropy of the Fe layers. The magnetoresistance curves showed an unusual shape, where up to three peaks were observed. Eight variables computer simulations, based on a phenomenological model that considers bilinear and biquadratic couplings between layers with cubic and in-plane uniaxial anisotropies, were used in order to calculate the best-fitting magnetization curves for the NiFe/Cu and Fe/NiFe/Fe/Cu multilayers. Both model and Mössbauer spectroscopy results showed that it is the rotation of the Fe magnetic moment from out-of-plane to in-plane orientation that provokes the unusual magnetoresistance curve shape. The observed reduction of the magnetoresistance amplitude with the addition of one monolayer of Fe in the NiFe/Cu multilayer was attributed to a less-effective spin-dependent scattering that occurs at Fe/Cu and Fe/NiFe interfaces than at the NiFe/Cu interfaces.     

Specific features of injection hardening of cracked concrete structures and buildings with polyurethanes

The procedure of renovation of damaged concrete matrices by injecting flowing polyurethane compositions is described. It is shown that the process of filling of cracks is accompanied by the penetration of injected compositions into the weakened zones and impregnation of the surface layers of concrete. It is confirmed that the components of polyurethane compositions undergo chemical interaction with the OH-groups of cement stone and mineral fillers of concrete. It is demonstrated that the concrete–transition-layer–polyurethane joints formed as a result of the injection guarantee the required serviceability of concrete structures and buildings. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 115–119, September–October, 2008.     

Preparation and Properties of Amorphous NiFe/Cu/NiFe Thin Films

The amorphous of Permalloy on the copper subtract was studied using composite electroplating method. A portion of hydrogen brings the counteraction on the surface of cathode leading nickel-iron alloys to be anomalous in the process of co-depositing. The results of X-ray diffraction (XRD) show that the Ni-Fe alloys layer is amorphous. The Giant Magneto -Impedance (GMI) effect of Ni-Fe alloys was obtained under the optimal conditions, dependence on the soft magnetic property of Ni-Fe amorphous thin film. As a result, the ratios△ Z/Z of NiFe/Cu/NiFe amorphous thin film are 30% at 40 kHz which is in low frequency. Furthermore, the GMI value of NiFe/Cu/NiFe amorphous thin film with a sandwich structure is higher than that of single-layer ferromagnetic films of the same thickness.     

Asymmetry of Magnetization Reversal of Pinned Layer in NiFe/Cu/NiFe/IrMn Spin-Valve Structure

Two types of asymmetry in giant magnetoresistance (GMR) are observed which are not related to a training effect, but indicate different mechanisms of magnetization reversal of the pinned layer in spin-valve (SV) structures for ascending and descending field scans. GMR, exchange bias and coercivity in Si/Ta/NiFe/Cu/NiFe/IrMn/Ta SV-structures were investigated as functions of the thickness of the nonmagnetic spacer. The spacer thickness effects are discussed in correlation with layers microstructure and interfaces morphology variations.     

Cu对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应影响的研究

用直流磁控溅射方法制备了NiFe/Cu/NiFe层状薄膜 ,研究了Cu膜宽度对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应的影响 ,结果表明 ,层状薄膜的巨磁阻抗效应随Cu膜宽度发生振荡现象 ;并提出了一个等效电路模型直观地解释了层状薄膜增强巨磁阻抗效应的机理