The magnetocaloric properties of a thin spacer of gadolinium (Gd) between layers of "strong" ferromagnets (relatively high Curie temperatures) are studied experimentally. It is found that, at room temperatures, the magnetocaloric efficiency Delta S/Delta H (Delta S is the isothermal magnetic entropy change and Delta H is the range of applied magnetic fields) of Gd spacer of thickness of 3 nm is up to two orders in magnitude higher than this value in an individual thicker (30 nm) Gd layer. This opens up opportunities for using the magnetocaloric effect in micro(nano)electronics and biomedicine using relatively weak magnetic fields H<1 kOe. The observed increase in the magnetocaloric efficiency is explained by the influence of direct exchange coupling between Gd spacer and its surroundings, which changes the distribution of magnetization in the spacer and, ultimately, its magnetocaloric potential. Keywords: magnetocaloric effect, magnetic heterostructures, exchange coupling at interfaces, Curie temperature.

The data on the EPR, photoluminescence (PL), and current transfer in porous silicon (PS) on KDB-0.3 and KES-0.01 Si, which was oxidized by 10-min isochronous thermal annealing in air at temperatures Tann from 20 to 900°C, as well as in HNO3, are presented in order to further clarify the nature of Pb centers of nonradiative recombination. The maximum PL quantum yield was observed during the chemical oxidation of PS on KDB-0.3 silicon. An anticorrelation of the PL and EPR intensities of Pb centers is observed in the range Tann = (20–300)°C. A nonmonotonic dependence of the EPR intensity of Pb centers on Tann with a minimum at approximately 700°C is revealed. The weak PL of PS with Tann of ~700°C accompanied by a minimum EPR signal from Pb centers means that other nonradiative-recombination centers arise after annealing. A decrease in the PS conductivity with an increase in Tann is associated with the decomposition of Si fibers in PS into small granules, through which discrete tunneling of current carriers occurs.

There are presented research data of ESR, photoluminescence (PL) and carrent transport in porous silicon (PS) on KDB-0.3 and KES-0.01 Si, oxidized by10 minute isochronous thermal annealing on air at temperatures Tann from 20°С to 900°С and also in HNO3 for the purpose of the further clearing of Pb - centres nature of no radiating recombination. Maximum quantum yield of PL was observed at chemical oxidation of the PS on silicon of KDB-0.3 mark.. Anticorrelation of PL and ESR intensities of Pb - centres in the range of Tann = (20-300) °С takes a place. . Nonmonotonic dependence of ESR intensity of Pb - centres vs Tann with a minimum nearby 700°С is found out. Weak PL in PS with Tann nearby 700°С at minimum of ESR of Pb - centres means occurrence with annealing of other no radiating recombination centres. Falling of conductivity of PS with growth of Tann is connected with disintegration of Si fibres in Ps on small granules through which there is a discrete tunneling of current carriers.

Porous silicon is formed using pulsed current with a pulse modulation varied in a range spanning five orders of magnitude, starting from a hundredth of a second, in order to achieve modulation of the properties of PS on the nanoscale. The PS is characterized by performing photoluminescence (PL), paramagnetic, and charge transport measurements. We find that the properties of prepared PS are greatly affected by the modulation period applied and depend on it in a nonmonotonic way. The intensity of orange-red PL exhibits a resonance-like behavior reaching a maximum at the modulation period in the range of 0.1–0.25 s. A correlation between the variation in PL intensity and the electron paramagnetic resonance signal is noticed. We show that PS with a porosity of 50% and a distance between pores of 10 nm is mainly consists of air and silicon oxide. In the prepared PS, the silicon, in the form of granules with a diameter of ≈1.5 nm arranged in chainlets, has a volume fraction on the order of 1%.

We experimentally study the interlayer interaction in a magnetic multilayer system ferromagnet/insulator/ferromagnet with different spacer thickness. The sign and the magnitude of the interaction can be deduced from the ferromagnetic resonance (FMR) peak shape rather than the FMR peak shift. The proposed technique allows studying the interlayer interaction using a single sample (without a reference sample for comparison).

We present a theoretical study of the ferromagnetic resonance in a system of two coupled magnetic layers. We show that an interaction between the layers leads to the occurrence of the so-called Fano resonance. The Fano resonance changes the shape of the ferromagnetic resonance peak. It introduces a peak asymmetry. The asymmetry type is defined by the sign of the interaction between the magnetic layers. Therefore, by studying the shape of the ferromagnetic resonance peaks, one can define the type of the interlayer coupling (ferromagnetic or antiferromagnetic).

AbstractPorous silicon is formed using pulsed current with a pulse modulation varied in a range spanning five orders of magnitude, starting from a hundredth of a second, in order to achieve modulation of the properties of PS on the nanoscale. The PS is characterized by performing photoluminescence (PL), paramagnetic, and charge transport measurements. We find that the properties of prepared PS are greatly affected by the modulation period applied and depend on it in a nonmonotonic way. The intensity of orange-red PL exhibits a resonance-like behavior reaching a maximum at the modulation period in the range of 0.1–0.25 s. A correlation between the variation in PL intensity and the electron paramagnetic resonance signal is noticed. We show that PS with a porosity of 50% and a distance between pores of 10 nm is mainly consists of air and silicon oxide. In the prepared PS, the silicon, in the form of granules with a diameter of ≈1.5 nm arranged in chainlets, has a volume fraction on the order of 1%.

Получение распыляемых композитных мишеней, содержащих фазы сплавов Гейслера Co 2 FeSi

The paper presents a method for manufacturing mechanically strong sputtering composite targets containing the phase of the Co2FeSi or Co2MnSi Heusler alloy of the stoichiometric composition, which can be used for fabrication of spin electronic devices by high-frequency magnetron deposition and pulsed laser deposition of thin films.

Nanostructured Co and permalloy films are fabricated on top of a polymethyl methacrylate (PMMA) colloidal crystals by magnetron sputtering. The influence of the geometry of the samples on the ferromagnetic resonance spectra is studied. A number of spin-wave resonances are found in the nanostructured system, while only a single resonance is observed in the spatially uniform flat film. The number of the observed resonance peaks increases with both the period of the colloidal crystal (120/340 nm) and the film thickness (20/90 nm). The micromagnetic simulations of the system show that the excited spin-wave modes are nonreciprocal because of nonzero toroidal momentum of the magnetization of the system. (C) 2017 Elsevier B.V. All rights reserved.

The peculiarities of absorption of rf electromagnetic radiation (ferromagnetic resonance) in multilayer NiFe/Ni0.65Cu0.35(d)/CoFe structures in a wide temperature range are analyzed. It is shown that the type of interaction of the NiFe and CoFe ferromagnetic films via a “weak” ferromagnetic Ni0.65Cu0.35 interlayer changes from antiferromagnetic to ferromagnetic upon cooling and a decrease in interlayer thickness d. The detected temperature dependence of the interlayer interaction indicates the possibility of observation of a strong magnetocaloric effect in the structures under investigation.

We present systematic experimental investigation and micromagnetic simulation of ferromagnetic resonance (FMR) in planar rectangular permalloy microstripes. The experimental microwave absorption was studied for different sample orientations in an external magnetic field. To analyze the FMR modes we developed the algorithm for the simulation of spectrum and spatial distribution of magnetization oscillations in dependence on swept external magnetic field based on numerical solution of Landau-Lifshitz-Gilbert equation. It was shown good agreement between experimental and model FMR spectra that enables the reliable visualization for spatial distributions of oscillating magnetization in modes of spin-wave resonances for different excitation conditions.

Представлены данные изменения свойств пористого кремния (ПК), сформированного при импульсной модуляции тока в диапазоне (0.1-1) Hz с целью нанометровой модуляции свойств ПК. Показано, что применение импульсного режима формирования ПК с периодом в десятые доли секунды может существенно повлиять на квантовый выход фотолюминесценции и другие свойства ПК. Имеется корреляция люминесцентных, электротранспортных и парамагнитных свойств ПК, сформированного в различных режимах. DOI: 10.21883/FTT.2017.02.44042.275

We present the data on changes in the properties of porous silicon formed at the current pulse modulation in the range of 0.1–1 Hz with the aim to modulate the properties of porous silicon in a nanoscale range. It is demonstrated that the use of the pulsed mode of formation of porous silicon with a period of a few tenths of a second can dramatically affect the photoluminescence quantum yield and other properties of the material. There is a correlation of the luminescent, electrotransport, and paramagnetic properties of porous silicon formed under different modes.

There are essential achievements in synthesis of interesting for creation of compact electronic memory switched by own current structures of spin valves and magnetic tunnel junctions with hysteretic current dependences of resistance. In the offered message the attention to discrepancy to physical principles of a hysteresis of resistance represented in publications is paid. It is schematically presented how the dependences of resistance on current should look not contradicting the energy conservation law for hysteresis dependence of resistance on current and corresponding volt-ampere characteristic.

We report a study of interlayer exchange interaction in multilayer CoPt/Co structures consisting of periodic CoPt multilayer film with an "easy axis" anisotropy and thick Co layer with an "easy plane" anisotropy separated by Pt spacer with variable thickness. The magnetooptical Kerr effect (MOKE) and ferromagnetic resonance (FMR) measurements show up the essentially non-collinear state of magnetic moments of the layers and strong exchange coupling between CoPt and Co subsystems. The estimation of effective anisotropy and exchange coupling in a simple model based on the Landau-Lifshitz-Gilbert equation describing magnetization dynamics was performed.

New data on the structure of the diluted magnetic semiconductor Si:Mn with the Curie point to 500 K synthesized by the laser method have been presented. High-resolution electron microscopy and diffraction in the directions 〈110〉 and 〈100〉 of epitaxial layers of the diluted magnetic semiconductor Si:15% Mn with the elimination of the contribution from the GaAs substrate and interface have been applied. It has been established that the diluted magnetic semiconductor Si:Mn is a previously unknown compound with the variable composition Si3 − x Mn x (0 < x < 1), single-phase diamond-like structure, high crystal perfection, and self-organized formation of the superlattice structure with the period of the triple distance between the nearest (110) atomic layers and the interval between the (110) layers doped with Mn atoms and oriented along the growth direction of the Si:Mn film. The layers Si:15% Mn (or Si2.5Mn0.5) consist of 15- to 50-nm blocks with the mutually perpendicular orientations of the superlattice modulations. Manganese atoms in the (110) layers doped with this impurity are located in the form of single-atom stripes, which alternate with the silicon single-atom stripes in agreement with the X-ray spectral analysis and ferromagnetic resonance data. The ferromagnetism of Si3 − x Mn x is associated with a specific feature of the impurity band.

We report the experimental observation of magnetic skyrmion-like states in patterned ferromagnetic nanostructures consisting of perpendicular magnetized Co/Pt multilayer film exchange coupled with Co nanodisks in vortex state. The magnetic force microscopy and micromagnetic simulations show that depending on the magnitude of Co/Pt perpendicular anisotropy in these systems two different modes of skyrmion formation are realized.