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Magnetic properties of two-phase granular semiconductor–ferromagnet GaSb–MnSb films obtained by pulsed laser deposition as a function of growth temperature and postgrowth annealing were stu-died.

We observed a temperature-controlled increase in the magnetic anisotropy and its dispersion in thin GaMnSb films with MnSb nanoinclusions obtained by pulsed laser deposition. The data of transmission electron microscopy indicate that in the samples, a transition of the crystalline structure of magnetic MnSb nanoinclusions from hexagonal (spatial group (sp. gr.) P63/mmc) to cubic (sp. gr. F-43m) takes place. Analysis of the temperature dependences of the magnetic moment m(T), measured using a SQUID magnetometer, obtained for both unannealed and annealed samples cooled in a zero magnetic field and a magnetic field of 10 kOe, indicates that this mechanism is not unique. In unannealed samples, the distribution of the magnetic anisotropy of MnSb nanoinclusions, determined from the dependences of m(T), is unimodal. In the annealed samples, the same dependence becomes multimodal. This means that several thermally activated processes occur in the samples during annealing, resulting in several “populations” of nanoinclusions present in the annealed thin films. The contribution to the increase in the magnetic anisotropy during annealing can result in the structural phase transition, the mismatch of the crystal lattices between MnSb and GaSb, an increase in the average volume of MnSb nanoinclusions, and a change in their stoichiometry.

The temperature behavior of the coercive field Hc(T) and the magnetic anisotropy in (CoFeB)x(LiNbOy)100 –x nanocomposite films with a ferromagnetic alloy content x = 33–48 at % near the metal–insulator transition (xc ≈ 42 at %) have been studied by the magnetometry and ferromagnetic resonance methods. The films were ensembles of CoFe granules with lateral sizes of 2–4 nm, which are highly elongated (up to 10–15 nm) in the nanocomposite growth direction and embedded in a LiNbOy matrix with a high content of magnetic Fe2+ and Co2+ ions (up to 3 × 1022 cm–3). A nonmonotonic behavior of Hc(T), viz., a sharp minimum at a temperature TF ≈ 50 K close to the blocking temperature ( $$T_{b}^{*}$$ ≈ 70 K) of the granule magnetic moment, has been detected in samples with x < 42 at %. The effective field of the perpendicular growth anisotropy (0.4–0.8 kOe) turns out to be an order of magnitude lower than the field of the granule shape anisotropy (about 7 kOe) and increases with x. The revealed peculiarities are explained by the fact that, apart from the ferromagnetic intergranular exchange interaction in an infinite cluster, the surface anisotropy effects involving magnetic ions in a thin layer adjacent to the cluster and responsible for the surface interaction fluctuations play a big role in the investigated percolation nanocomposites, enhancing the nanocomposite demagnetization at T ≈ TF ~ $$T_{b}^{*}$$ .

—The effect of laser pulse energy E on the possibility of forming of a homogeneous “high-temperature” ferromagnetic phase in MnxSi1 – x (x ≈ 0.5) alloy films grown by pulsed laser deposition onto an Al2O3 (0001) substrate has been studied. The high-temperature phase with manganese concentration x ≈ 0.53 and the Curie temperature TC ~ 200–300 K is shown to form near the substrate at the initial stage of the film growth. In this case, high values E ≥ 6.8 J/cm2 favor the stabilization of this phase over all film thickness, while low values E = 2.6–5.7 J/cm2 lead to a decrease in the manganese concentration in the upper film layer and the formation of additional “low–temperature” phase with TC ≈ 30–50 K provided by silicides MnSi and Mn4Si7 crystallites.

Conditions and mechanisms of controlled variation of the magnetic anisotropy of GaMnSb films containing magnetic MnSb nanoinclusions by means of heat treatment have been determined. For this purpose, the temperature and magnetic-field dependences of the magnetic moments of samples before and after thermal annealing were measured using a SQUID magnetometer. It is established that the heat treatment of GaMnSb films leads to a significant increase in the values of characteristics determined by the magnetic anisotropy, including the growth of blocking temperature (from 95 to 390 K) and the magnetic anisotropy field (from 330 to 630 Oe). Results of transmission electron microscopy investigation indicate that a change in the magnetic anisotropy of GaMnSb films as a result of their thermal annealing can be related to a transition of the crystalline structure of magnetic MnSb nanoinclusions from hexagonal (space group P62/mmc) to cubic (space group F-43m).

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

Thin films of Si1−xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1−xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1−xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1−xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤ 4.4 J/cm2.

Comparative examination of magnetotransport properties of nonstoichiometric Si1–xMnx alloys with roughly the same (δх/x ≈ 7%) excess of Mn relative to silicides Mn4Si7 and MnSi has been performed. Films of Si1–xMnx (х ≈ 0.39 and 0.535) with a thickness of 60–70 nm have been fabricated by means of pulsed laser deposition on Al2O3 (0001) substrates at a temperature of 340°С. It has been found that the excess of Mn produces the strongest effect on the Curie temperature in the case of MnSi (ТС increases from 30 K to 300 K and higher), while no such effect is observed in Mn4Si7. This may be attributed to strong nonmagnetic disorder in Si1–xMnx with x ≈ 0.39 and the associated unusual behavior of negative magnetoresistance (NMR): The NMR varies linearly with magnetic field at В ≤ 1.3 T and exhibits almost no temperature dependence at T = 40–85 K.

The structural, transport, and magnetic characteristics of polycrystalline Mn x Si1–x (x ≈ 0.51–0.52) films grown by pulsed laser deposition onto Al2O3(0001) substrates when the low-energy components are deposited owing to collisions with the atoms of the buffer gas have been studied in the “shadow” geometry. The magnetization of these films is determined by two ferromagnetic phases—the high-temperature phase with the Curie temperature T C ≈ 370 K and the low-temperature one with T C ≈ 46 K. The anomalous Hall effect changes sign from positive to negative with a decrease in temperature. The sign change occurs in the temperature range of 30–50 K; the specific value of this temperature depends on the thickness of the Mn x Si1–x film. The results can be interpreted in terms of the structural self-organization related to the formation of two layers in the course of film growth. These layers have nearly the same chemical composition but significantly differ in the shapes and sizes of crystallites. This leads to a drastic difference in the values of T C and in the value and the sign of the anomalous Hall effect for such layers.

Effect of charge carriers concentration on magnetic parameters of the ferromagnetic MnSb nanoclusters as well as opposite effect of cluster magnetization on spin polarization of holes and magnetoresistance were observed in GaSbMn thin films. Microwave magneto-resistance effect is evidence of the charge carriers spin filtering by ferromagnetic clusters.

The paper reports on the comprehensive study of properties of nonstoichiometric Si1−xMnx alloys slightly enriched in Mn (x≈0.51–0.55) as compared to the stoichiometric monosilicide MnSi. Mosaic type Si1−xMnx films 55–70 nm in thickness were produced by the pulsed laser deposition (PLD) method onto the single crystalline Al2O3 substrates at 340 °C. The Curie temperature TC in nonstoichiometric Si1−xMnx (x≈0.52–0.55) films exceeds room temperature, while in their stoichiometric counterpart, MnSi, the TC value does not exceed ≈30 К. The consistent data on anomalous Hall effect and transverse Kerr effect prove the global character of ferromagnetic (FM) order caused by magnetic defect formation rather than the presence of FM clusters. Аt Mn content x≤0.55, the magnetization data testify to a good homogeneity in the distribution of magnetic defects without their segregation: variations of the saturation magnetization Ms do not exceed 6% in the temperature range T=10–100 К and are well described by the Bloch law. It is also revealed that textured high-quality Si1−xMnx films with x≈0.52 and ТС~300 К could be formed by PLD method in the “shadow” geometry (at lower energy of deposited atoms).

The influence of the charge carrier concentration on the magnetic properties of GaSb-MnSb alloys is studied. The ferromagnetism of GaSb-MnSb films is caused by the presence of MnSb granules and manifests itself in both magnetometric measurements and the presence of an anisotropic magnetoresistance and the anomalous Hall effect. Electric conduction is executed by charge carriers (holes) in a GaSb matrix. The magnetization of clusters depends on stoichiometry and the concentration of Mn2+ and Mn3+ ions, which is specified by the film growth conditions. At high film growth temperatures, ferromagnetic clusters containing Mn2+ ions mainly form. At low growth temperatures, an antiferromagnetic phase containing Mn3+ ions forms.

It has been found that the Curie temperature (T C ≈ 300 K) in nonstoichiometric Si1 − x Mn x alloys slightly enriched in Mn (x ≈ 0.52–0.55) in comparison to the stoichiometric manganese monosilicide MnSi becomes about an order of magnitude higher than that in MnSi (T C ∼ 30 K). Deviations from stoichiometry lead to a drastic decrease in the density of charge carries (holes), whereas their mobility at about 100 K becomes an order of magnitude higher than the value characteristic of MnSi. The high-temperature ferromagnetism is ascribed to the formation of defects with the localized magnetic moments and by their indirect exchange interaction mediated by the paramagnetic fluctuations of the hole spin density. The existence of defects with the localized magnetic moments in Si1 − x Mn x alloys with x ≈ 0.52–0.55 is supported by the results of numerical calculations performed within the framework of the local-density-functional approximation. The increase in the hole mobility in the nonstoichiometric material is attributed to the decay of the Kondo (or spin-polaron) resonances presumably existing in MnSi.

Using pulsed laser deposition, we have grown n-ZnO/p-GaN, n-ZnO/i-ZnO/p-GaN and n-ZnO/n-Mg0.2Zn0.8O/i-Cd0.2Zn0.8O/p-GaN light-emitting diode (LED) heterostructures with peak emission wavelengths of 495, 382 and 465 nm and threshold current densities (used in electroluminescence measurements) of 1.35, 2, and 0.48 A cm-2, respectively. Because of the spatial carrier confinement, the n-ZnO/n-Mg0.2Zn0.8O/i-Cd0.2Zn0.8O/p-GaN double heterostructure LED offers a higher electroluminescence intensity and lower electroluminescence threshold in comparison with the n-ZnO/p-GaN and n-ZnO/i-ZnO/p-GaN LEDs.

A Langmuir probe was used to study the erosion plume produced during the ablation of a tantalum target in vacuum by radiation from an excimer laser at 308 nm. The spatial and temporal dependences of the electron and ion currents of the probe were obtained in real time. The electron temperature of different regions of the plume at different distances from the target was measured for the first time from a series of dependences of the electron probe current on the probe voltage. The nonuniformity of the electron temperature and its lowering in different plume regions with increasing expansion time were determined. The ion density in the plume was determined at different distances from the target.

An experimental investigation was made of the formation of a channel in the process of hole punching in glass by pulse-periodic radiation from a cw CO2 laser in the presence of a concurrent stream of air reaching the target. The dependence of the punching velocity on the air pressure in the laser-radiation intensity range 40–270 kW cm-2 and the rate of change of the hole radius were determined. The frequency of oscillations of the channel walls in the course of punching was measured. Formation of quasiperiodic structures on the channel walls was observed.

Thin films of Mn x Si1−x alloys with different Mn concentration grown by the pulsed-laser deposition (PLD) method onto the Al2O3 (0001) substrate were investigated in the temperature range 4–300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies and magnetic fields . For samples with , FMR data show clear evidence of ferromagnetism (FM) with high Curie temperatures . These samples demonstrate the complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second-order easy-plane anisotropy contribution and the additional fourth-order anisotropy contribution with the easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch.

Infrared-luminescence diagnostics, based on vibrational—rotational bands of the CO2 molecule with the wavelengths 2.7 and 4.3 μm, was used in a study of the spatial structure of the characteristics of the active medium of an industrial fast-flow CO2 laser excited by a self-sustained glow discharge with orthogonally sectioned electrodes. The distributions of the infrared luminescence intensity were determined along and across the gas flow in the gas-discharge chamber at various heights above the anode. The experimental infrared luminescence data were used to calculate the spatial distribution of the vibrational temperatures of the coupled and asymmetric modes of the CO2 molecule in the downstream direction. The feasibility of monitoring the output power of an industrial laser on the basis of the 4.3 μm infrared luminescence band was demonstrated.

Experimental and theoretical investigations were made of turbulent diffusion in an industrial CO2 laser with crossed electrodes. The particle diffusion reduced considerably the spatial inhomogeneity of the gain. The results obtained were used to propose a new method for the determination of the turbulent diffusion coefficient.

We present a comparative study of the anomalous Hall effect (AHE) and of the transverse Kerr effect (TKE) in the nonstoichiometric alloys. The data on AHE and TKE are consistent with each other and clearly indicate the intrinsic above room-temperature ferromagnetic order in the studied samples. We argue that this order is not produced by the phase segregation effects, but rather has a global character, while even a small level of the nonstoichiometry in alloys drastically changes their magnetic, electrical, optical and magneto-optical properties as compared to those of the stoichiometric manganese monosilicide MnSi. We propose a qualitative explanation of the obtained experimental results in the frame of the model of defect-induced ferromagnetic order using the first-principles calculations of the electronic and magnetic structure of the system.

The coefficients of ambipolar diffusion of lithium, sodium, nickel, indium, platinum, and lead ions were measured by laser optogalvanic spectroscopy in the upper cone of a luminous gas-air flame at atmospheric pressure in the absence of an electric field in the flame. The coefficients of diffusion and mobility of the singly charged ions of these elements were calculated from the experimental data.