Single-crystal (001) rutile plate was irradiated intensively with 40 keV argon ions. Then, electromigration of oxygen vacancies was done in the irradiated rutile. The effect the concentration and charge state of oxygen vacancies has on the color, optical absorption spectra, and photoluminescence of rutile is shown.

In this work, we have studied the microstructure and unusual ferromagnetic behavior in epitaxial tin dioxide (SnO2) films implanted with 40 keV Co+ ions to a high fluence of 1.0 × 1017 ions/cm2 at room or elevated substrate temperatures. The aim was to comprehensively understand the interplay between cobalt implant distribution, crystal defects (such as oxygen vacancies), and magnetic properties of Co-implanted SnO2 films, which have potential applications in spintronics. We have utilized scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), differential thermomagnetic analysis (DTMA), and ferromagnetic resonance (FMR) to investigate Co-implanted epitaxial SnO2 films. The comprehensive experimental investigation shows that the Co ion implantation with high cobalt concentration induces significant changes in the microstructure of SnO2 films, leading to the appearance of ferromagnetism with the Curie temperature significantly above the room temperature. We also established a strong influence of implantation temperature and subsequent high-temperature annealing in air or under vacuum on the magnetic properties of Co-implanted SnO2 films. In addition, we report a strong chemical effect of ethanol on the FMR spectra. The obtained results are discussed within the model of two magnetic layers, with different concentrations and valence states of the implanted cobalt, and with a high content of oxygen vacancies.

In this work, we have studied microstructure and unusual ferromagnetic behavior in cobalt (Co)-implanted epitaxial tin dioxide (SnO2) films. The study was aimed to provide a comprehensive understanding of the interplay between cobalt implant distribution, crystal defects, such as oxygen vacancies, and magnetic properties in Co-implanted SnO2 films, which has potential applications in spintronics and memristor devices. The scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), differential thermo-magnetic analysis (DTMA), and ferromagnetic resonance (FMR) were employed for investigations of SnO2 films implanted with 40 keV Co+ ions at room or the elevated temperatures of substrate. The experimental data showed that the Co ion implantation with high fluence of 1.0 1017 ions/cm2 induces significant changes in the microstructure of SnO2 films, leading to the appearance of ferromagnetism with the Curie temperature significantly above room temperature. Strong influence of implantation temperature and subsequent high-temperature annealing in air or in vacuum on magnetic properties of Co-implanted SnO2 films were established. Moreover, the chemical effect of ethanol on FMR spectra were observed. The obtained results are discussed within the model of two magnetic layers with different concentration and valence states of the implanted cobalt and with high content of oxygen vacancies.

The optical properties of erbium-doped yttrium iron garnet (Er:YIG) thin films have been studied at temperatures between 1.6 K and 260 K. Single crystal YIG thin films on GGG (Gd3Ga5O12) have been implanted with 20 keV Er+ ions to the fluences of (0.5 or 1.0) x 10(16) ion/cm(2). Erbium concentration has been kept on a level preventing a detrimental effect on the magnetic properties of the YIG garnet while providing the ion ratio enough for intense photoluminescence. Raman spectra for the YIG films on GGG substrate which are similar to the literature data have been observed. No effect of the erbium implantation on Raman peaks has been revealed and explained by the small thickness of the implanted layer. Photoluminescence signals appearing with temperature cooling between 680 nm and 720 nm have been observed and attributed to the emission from the erbium ions. Our result reveals that doping YIG by Er can be useful for tailoring the magneto-optical properties of YIG.

Manganese-doped TlInS2 (TlInS2+Mn) layered semiconductors with different doping concentrations of about 0.1 and 0.3 at. percent were investigated. Photo-induced current transient spectroscopy (PICTS) measurements in the temperature range of 80 and 300 K have been made for identifying energy levels related to Mn dopant within the electronic bandgap of TlInS2+Mn crystal. Optical absorption spectra in the photon energy range of similar to 1.8-3.1 eV have been extracted by fitting the transmittance spectra of TlInS2+Mn recorded at the temperatures varied from similar to 40-300 K. A redshift trend of the absorption edge with increasing of temperature was observed. On the other hand, a blue shift in the absorption edge with Mn doping was observed in the absorption spectra. The Mn dopant induced photoluminescence (PL) was also investigated in the visible region ranging from 320 to 960 nm. Seven peaks were observed in the PL spectra of Mn doped TlInS2 crystal in the regions both similar to 960-620 nm (similar to 1.3-2 eV) and similar to 620-320 nm (similar to 2-3.8 eV) due to the electronic states of Mn ions. Laser- -induced breakdown spectroscopy (LIBS) technique was applied to establish of the elemental chemical composition and to confirm presence of each constituent element in TlInS2:Mn. The dc magnetization measurements of TlInS2+Mn performed in a wide temperature range of similar to 5 and similar to 300 K revealed different (diamagnetic and paramagnetic states) magnetic phases inside the studied temperature range. The X-band electron paramagnetic resonance (ESR) experiments were carried out in the low-temperature phase of TlInS2+Mn to probe the structure of Mn centers in TlInS2. The measurements revealed that the ESR spectrum changes drastically in the low-temperature phase of TlInS2+Mn bulk sample. Finally, a detailed density functional theory (DFT) based computational investigation of electronic band structures, density of states and optical properties of TlInS2+Mn compound has been performed. The results of ab - initio calculations are discussed for three possible states when the manganese atom was doped by replacing either the Tl, In or S atoms in the unit cell of TlInS2. Additionally, the effect of interstitial Mn dopant on the electronic structure and optical properties of TlInS2 material has been simulated.

As a result of enormous progress in nanoscale electronics, interest in artificial intelligence (AI) supported systems has also increased greatly. These systems are typically designed to process computationally intensive data. Parallel processing neural network architectures are particularly noteworthy for their ability to process dense data at high speeds, making them suitable candidates for AI algorithms. Due to their ability to combine processing and memory functions in a single device, memristors offer a significant advantage over other electronic platforms in terms of area scaling efficiency and energy savings. In this study, single-layer and bilayer metal-oxide HfOx and TiOy memristor devices inspired by biological synapses were fabricated by pulsed laser and magnetron sputtering deposition techniques in high vacuum with different oxide thicknesses. The structural and electrical properties of the fabricated devices were analysed using x-ray reflectivity, x-ray photoelectron spectroscopy, and standard two-probe electrical characterization measurements. The stoichiometry and degree of oxidation of the elements in the oxide material for each thin film were determined. Moreover, the switching characteristics of the metal oxide upper layer in bilayer devices indicated its potential as a selective layer for synapse. The devices successfully maintained the previous conductivity values, and the conductivity increased after each pulse and reached its maximum value. Furthermore, the study successfully observed synaptic behaviours with long-term potentiation, long-term depression (LTD), paired-pulse facilitation, and spike-timing-dependent plasticity, showcasing potential of the devices for neuromorphic computing applications.

The electron paramagnetic resonance (EPR) spectra of oxygen-deficient rutile TiO2 – δ under photoexcitation at low temperatures in the range of 15–40 K were measured. Excluding the early described Ti3+ centers, concentration of which is independent of photoexcitation, new EPR signals appear at various wavelengths (λ) of photoexcitation taken in the range 400–460 nm. From the analysis of the EPR data we conclude that the observed EPR signals can be attributed to either the positive-charged oxygen vacancies ( V_O^ + ) with S = 1/2 (upon photoexcitation with λ ≤ 420 nm only), or more complex defects such as positively-charged [Ti3+–VO]+ pairs with S = 1/2 and neutral complexes of (Ti3+–VO–Ti3+) with S = 1. The latter is observed upon photoexcitation with a wavelength above 420 nm.

The high-dose implantation of Co+ ions into the rutile (TiO2) structure induces the formation of ferromagnetism and two magnetic phases in it: metallic cobalt nanoparticles and a divalent cobalt ion solid solution. The effect the temperature and orientation of the TiO2 substrate have on the ferromagnetism and magnetic phase composition of rutile upon ion exposure and subsequent annealing in air or a vacuum is demonstrated.

Magnetic nanoparticles embedded into semiconductors have current perspectives for use in semiconducting spintronics. In this work, 40 keV Fe+ ions were implanted in high fluences of (0.5 ÷ 1.5) × 1017 ion/cm2 into an oxide semiconductor and single-crystalline TiO2 plates of rutile structure with (100) or (001) face orientations. Microstructure, elemental-phase composition, and magnetic properties of the Fe-ion-implanted TiO2 were studied by scanning and transmission electron microscopies (SEM and TEM), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies, as well as vibrating-sample magnetometry (VSM). The high-fluence ion implantation results in the formation of magnetic nanoparticles of metallic iron beneath the irradiated surface of rutile. The induced ferromagnetism and observed two- or four-fold magnetic anisotropy are associated with the endotaxial growth of Fe nanoparticles oriented along the crystallographic axes of TiO2.

A monocrystalline rutile (TiO2) plate implanted with cobalt ions at a fluence of 1.25∙1017 ions/cm3 with energy 40 keV at constant current density in the ion beam of 2 μA/cm2 when the temperature of the irradiated substrate was maintained at 620°C was studied using light reflection and transmission spectroscopy in the visible spectral region. The spectral dependences of the optical parameters of the modified layer were obtained. The calculated optical Tauc gap of the layer was 0.2–0.3 eV.

The results of a study of heavy implantation of a LiNbO3 crystal with iron ions are reported for the first time. The X-cut LiNbO3 substrate was implanted with 40-keV Fe+ ions to the fluence of 1.5·1017 ions/cm2. The sample reveals pronounced ferromagnetic properties at room temperature. However, the ferromagnetic response observed in the iron-implanted LiNbO3 differs from the magnetic behavior of other oxides implanted with iron ions under the same conditions. This difference occurs from the unusual magnetic phase composition of the implanted surface layer of the LiNbO3 in which the iron implant precipitates in the form of the nanoscale alloy of metallic iron with niobium. Based on Mössbauer spectroscopy data, we estimated the Nb content in the ion-synthesized nanosized alloy as ~12 at.%, which is much higher than the solid solubility limit of Nb in bulk Fe.

Abstract The dielectric constant measurements of Fe implanted TlInS2 and TlGaSe2 crystals without and under application of constant magnetic field have been performed. It has been observed that the implantation of the crystals with Fe ions caused the formation of ferromagnetic layer in the irradiated region, which leads to considerable shifts of the successive incommensurate and commensurate phase transitions to high temperatures in the heating regime. Remarkable shifts of the phase transition temperatures back to the low temperature region on heating of the samples were observed on applying the magnetic field perpendicularly to the implanted surface. None changes of the phase transition temperature points on measurements of the samples have been observed in cooling regime. The obtained results are interpreted as magnetodielectric effects that resulted from magnetoelectric coupling between ferromagnetic and ferroelectric constituents of the composite structure.

Objects of the study were colorless single crystals of quartz with a total amount of impurities lesser than 1%. Implantation of vanadium ions into the quartz structure was carried out parallel to the symmetry axis C. Irradiation doses varied from 0.75 × 1017 to 1.5 × 1017 ion/cm2. With the purpose to anneal radiation defects and to redistribute the implanted vanadium admixture, the post-implanting heat treatment was carried out in the air atmosphere, within the range 200–1000 °C. There was solved issue of ion-beam modification of the colorimetric properties of the quartz matrix with simultaneous control of change in the nature of color of the piezo quartz raw material. In result of the study, samples with annealing temperatures of 383 and 585 °C were investigated most thoroughly by methods of adsorption optical spectroscopy. The quartz sample with annealing temperature 383 °C has acquired an olive-green color due to formation of oxide nanoprecipitates of vanadium ions with different valences: V2+, V3+, V4+. The quartz sample with annealing temperature 585 °C become discolored in result of oxidation of vanadium ions and their transition in the pentavalent state V5+.

The point defects have been produced in the rutile structure by irradiation of a single crystalline (001)-TiO2 rutile platet wih 40 keV Ar+ ions. It is found that Ar-ion bombardment of rutile results in a large number of positively charged oxygen vacancies and, as a consequence, leads to a change in the valence of neighbouring Ti cations. Electron paramagnetic resonance (EPR) of Ar-ion irradiated TiO2 rutile is studied in detail. The analysis of angular , temperature dependences of EPR spectra makes it possible to conclude that EPR signals are associated with Ti3+ ions in the sixfold symmetric environment. In addition to the main signal from even titanium isotopes, eight equidistant weak lines are observed due to the hyperfine interaction typical for two titanium isotopes: 47Ti with a nuclear spin I = 5/2 (natural abundance of 7.4%) and 49Ti with a nuclear spin I = 7/2 (natural abundance of 5.4%). By comparing the g-tensor components with the reference data it is concluded that these Ti3+-based centers in Ar-ion implanted rutile were not described before.

Here we present the measurements of the temperature dependence of resistance, transverse and longitudinal magnetoresistance (MR) in nanocrystalline iron films in the temperature range 2-300 K and the sweep of the magnetic field up to 8 T. Thin nanocrystalline films of α-iron phase with 80 nm thickness were obtained by ion-beam assisted deposition on a silicon substrate. In addition to the shape anisotropy, the obtained iron films exhibited perpendicular magnetic anisotropy (PMA), which disappeared after annealing the films at a temperature of 450 o C in a vacuum. The effect of PMA on the sign and magnitude of the MR of iron films, as well as on the magnetic field dependences of the magnetoresistive effect, recorded at different orientations of the external magnetic field with respect to the film plane and current direction, is experimentally shown. The results obtained are discussed in the framework of modern views on the processes of charge transfer in a weakly disordered ferromagnetic films with different magnetic anisotropy and domain structure when a weak (less than the saturation field of magnetization) or strong (higher than the saturation field) external magnetic field is applied. Keywords: nanocrystalline iron films, perpendicular magnetic anisotropy, magnetoresistance, anisotropic magnetoresistance, magnon magnetoresistance, percolation, weak localization.

In this work, we report on the endotaxial growth of α-Fe nanoparticles in the near-surface layer under high-fluence iron ion implantation of the single-crystal magnesium oxide substrate. Comprehensive Mössbauer effect and magnetometry studies show that the implanted sample reveals a pronounced ferromagnetic response even at room temperature, and the α-Fe nanoparticles serve as its main source. The broad band at ~1000 Oe in the X-band magnetic resonance spectra originates from the α-Fe fraction. It manifests the properties of the easy-plane system with the four-fold in-plane anisotropy. The last indicates that the α-Fe nanoparticles are coherently incorporated into the host MgO matrix.

Palladium-iron alloys produced by high-dose implantation of iron ions into epitaxial palladium films were investigated with the ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal distinct multiple FMR responses depending on the dose of iron ion implantation. The post-implantation annealing at 770 K does not bring the implanted films to a homogeneous solid solution state, as might be expected from the Pd-Fe phase diagram. On the contrary, the system approaches a stable state composed of several magnetic phases. FMR spectra exhibit an angular behavior specific for a stack of interacting magnetic layers. This observation, correlated with the magnetometry data, indicates that the palladium-iron binary alloy has a previously unknown tendency towards spinodal decomposition into isostructural phases with well-defined iron concentrations and, accordingly, with different temperatures of ferromagnetic ordering and saturation magnetizations.

Various types of nanowires obtained by matrix synthesis --- homogeneous (from iron) and heterogeneous (layered) --- have been studied. A technique for obtaining arrays of layered nanowires with alternating thin layers of magnetic and non-magnetic metals (Co/Cu, Ni/Cu) has been developed and described. Microscopy methods (SEM and TEM with elemental analysis) have been used to study the topography of the resulting structures, the diameters of nanowires and the thicknesses of individual layers, and the features of interlayer interfaces. Methods of synthesis of nanowires with thin layers and clear boundaries are proposed --- dilution of the electrolyte, use of a reference electrode, control of the leaked charge. Layered nanowires have been studied by magnetometry methods and it has been shown that the magnetic properties of an array of layered nanowires (in particular, the direction of the axis of light magnetization in the Co/Cu-NP array) depend not only on the aspect ratio of the magnetic layer, but also on the ratio of the thickness of the magnetic metal layer to the thickness of a non-magnetic spacer (copper layer). The nuclear magnetic resonance (NMR) method was used to study two types of nanowires. The NMR method (on 59-Co nuclei) studied the layer structures of Co/Cu: it is shown that in nanowires with layers of smaller thickness (and, accordingly, with a large contribution of interfaces), a large proportion of Co atoms coordinated by Cu atoms is observed. The high proportion of atoms coordinated by copper suggests that an admixture of copper enters the cobalt layers. Homogeneous iron nanowires (NMR on 57-Fe nuclei) were compared with bulk iron samples. A shift of the line towards high frequencies (by 0.3 MHz) was detected, indicating an increase in the field by about 0.2 T. A significant broadening of the line and a decrease in the spin-lattice relaxation time may indicate a significant variation in the local magnetic field values. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, NMR.

We have performed full-stack research of Pd1−xFex and Pd1-xCox (x = 0.01–0.1) alloys. At the first stage, the occurrence of impurity ferromagnetism in the considered alloys was studied employing the density functional theory (DFT). At the second stage, magnetic impurities of Fe and Co atoms were implanted into epitaxial Pd thin films to verify the DFT results. The magnetic properties of implanted Pd films were investigated by a Vibrating Sample Magnetometer (VSM) in the temperature range from 5 to 300 K. It has been established that VSM results are in good agreement with ab initio calculations. In particular, 4 and 5 µB for Co found from VSM for x = 0.025 and x = 0.035 agree well with DFT value of 5.5 µB for x = 0.025.

We report investigation of ferromagnetic resonance phenomenon in ferromagnetic thin films with essentially non-uniform composition. Epitaxial Pd-Fe thin film with linear distribution of Fe content across the thickness is used as the model material. Anomalous perpendicular standing spin waves are observed and quantified using the collective dynamic equation. Numerical analysis yields the exchange stiffness constant for diluted Pd-Fe alloy $D=2A/\mu_0M_s=15$~T$\cdot$nm$^2$ and the ratio of the effective magnetization to the saturation magnetization $M_{eff}/M_s=1.16$. It is demonstrated that, overall, engineering of thin films with non-uniform composition across the thickness can be used for high-frequency or low-field magnonic operations using exchange spin waves.