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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 study, the method of thermal decomposition of iron(III) oleate at different ratios of oleic acid and octadecene-1 was used to obtain iron oxide nanoparticles (IONPs). Transmission electron microscopy (TEM) showed that they all had a spherical shape and a diameter of 8–9 nm, and FT-IR spectroscopy revealed the presence of oleate shells in them, which ensure the stability of the colloidal solutions of these nanoparticles in nonpolar solvents. For all synthesized IONPs, the sizes of the crystalline core formed by iron oxides were determined using X-ray diffraction analysis and magnetometry. The sizes of the oleate protective shells were established by comparison with the TEM data. These values were in agreement with those from the literature.

This study demonstrates capabilities of a molecular beam epitaxy method for the deposition of ferromagnetic Pd–Fe alloy thin films with variable compositions across film thickness. It is proposed as a technological route to synthesize graded magnetic materials possessing unusual physical properties. A particular approach to realize a concentration profile through temperature control of an effusion cell during deposition is described in detail. Using this technique, graded ferromagnetic films were synthesized and characterized to reveal the possibility of controlling the spectrum of standing spin waves in them. Limitations of creating Pd–Fe films magnetically profiled across the thickness are discussed, associated with the thermal inertia of effusion cells and possible phase separation. [ABSTRACT FROM AUTHOR]

Increasing the efficiency of upconversion luminophores is an important problem in materials science. Here we report on approach of use of disordered crystals namely solid solutions BaY1.8Lu0.2F8 doped with Er3+ ions to improve spectral characteristics and efficiency of upconversion from near IR spectral region. It is shown that investigated compound provide up to 9.4% of external energy yield of the up-conversion luminescence at an excitation power density of 6 W/cm2 at 1532 nm for the 10 at.% of Er3+ doping. Also the investigated crystals of BaY1.8Lu0.2F8:Er3+ allow the control of the CCT parameter in the range of 2384–5149 K by changing the concentration and power density of the excitation. Advantages revealed in this work for crystalline compounds BaY1.8Lu0.2F8:Er3+ such as wide absorption bands in the infrared spectral range, a high external energy yield, and a controllable distribution of intensity of luminescence bands makes them prospective to improve the efficiency of double-sided solar cells

A method for the design and synthesis of a metallopolymer composite (CoNP) based on cobalt nanoparticles using the hyperbranched polyol process was developed. It was shown that hyperbranched polyester polyols in a melted state can be both a reducing agent and a stabilizer of metal nanoparticles at the same time. The mechanism of oxidation of hyperbranched polyol was studied using diffuse reflectance IR spectroscopy. The process of oxidation of OH groups in G4-OH started from 90 °C and finished with the oxidation of aldehyde groups. The composition and properties of nanomaterials were determined with FT-IR and UV-Vis spectroscopy, Nanoparticle Tracking Analysis (NTA), thermogravimetric analysis (TG), powder X-ray diffraction (XRD), NMR relaxation, and in vitro biological tests. The cobalt-containing nanocomposite (CoNP) had a high colloidal stability and contained spheroid polymer aggregates with a diameter of 35–50 nm with immobilized cobalt nanoparticles of 5–7 nm. The values of R2 and R1 according to the NMR relaxation method for CoNPs were 6.77 mM·ms−1 × 10−5 and 4.14 mM·ms−1 × 10−5 for, respectively. The ratio R2/R1 = 0.61 defines the cobalt-containing nanocomposite as a T1 contrast agent. The synthesized CoNPs were nonhemotoxic (HC50 > 8 g/mL) multifunctional reagents and exhibited the properties of synthetic modulators of the enzymatic activity of chymosin aspartic proteinase and exhibited antimycotic activity against Aspergillus fumigatus. The results of the study show the unique prospects of the developed two-component method of the hyperbranched polyol process for the creation of colloidal multifunctional metal–polymer nanocomposites for theranostics.

Results are presented from studying the magnetostatic and magnetoresonant properties of a thin-film bilayer Fe3Al/Pt structure synthesized via molecular beam epitaxy. Magnetometry and ferromagnetic resonance data indicate the four-fold in-plane magnetocrystalline anisotropy of the Fe3Al layer. The magnetic field dependence of the voltage induced by the inverse spin Hall effect is measured under conditions of spin pumping, and the quantitative characteristic of the spin-charge transformation in platinum (the spin Hall angle) is estimated as θSH = 0.030 ± 0.005. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Single-layer vanadium nitride (VN) and bilayer Pd0.96Fe0.04/VN and VN/Pd0.92Fe0.08 thin-film heterostructures for possible spintronics applications were synthesized on (001)-oriented single-crystalline magnesium oxide (MgO) substrates utilizing a four-chamber ultrahigh vacuum deposition and analysis system. The VN layers were reactively magnetron sputtered from a metallic vanadium target in Ar/N2 plasma, while the Pd1−xFex layers were deposited by co-evaporation of metallic Pd and Fe pellets from calibrated effusion cells in a molecular beam epitaxy chamber. The VN stoichiometry and Pd1−xFex composition were controlled by X-ray photoelectron spectroscopy. In situ low-energy electron diffraction and ex situ X-ray diffraction show that the 30 nm thick single-layer VN as well as the double-layer VN(30 nm)/Pd0.92Fe0.08(12 nm) and Pd0.96Fe0.04(20 nm)/VN(30 nm) structures have grown cube-on-cube epitaxially. Electric resistance measurements demonstrate a metallic-type temperature dependence for the VN film with a small residual resistivity of 9 μΩ·cm at 10 K, indicating high purity and structural quality of the film. The transition to the superconducting state was observed at 7.7 K for the VN film, at 7.2 K for the Pd0.96Fe0.04/VN structure and at 6.1 K for the VN/Pd0.92Fe0.08 structure with the critical temperature decreasing due to the proximity effect. Contrary to expectations, all transitions were very sharp with the width ranging from 25 mK for the VN film to 50 mK for the VN/Pd0.92Fe0.08 structure. We propose epitaxial single-crystalline thin films of VN and heteroepitaxial Pd1−xFex/VN and VN/Pd1−xFex (x ≤ 0.08) structures grown on MgO(001) as the materials of a choice for the improvement of superconducting magnetic random access memory characteristics.

The synthesis of the NiCr2O4 compound with the spinel structure via the high-temperature solid-state reaction leads to different deviations of the cationic composition from the nominal depending on the atmosphere in the furnace chamber. The samples prepared from the same starting NiO and Cr2O3 compounds but in different atmospheres differ in phase composition and orbital and spin ordering temperatures. We find that a common route of synthesis in the air and a possible presence of the Ni2O3 in initial NiO lead to the incorporation of the Ni3+ ions into the octahedral sites regularly occupied by the Cr3+ ions. This results in a decrease in the orbital ordering and an increase in the Nèel temperatures. We propose that the Nèel temperature value serves as a measure of a departure of a composition from the nominal NiCr2O4. The lowest Nèel temperature among our series was TN = 63 K which we consider the closest to the intrinsic quantity of the NiCr2O4 compound.

This work is devoted to the study of thermometric performances of Nd3+ (0.1 or 0.5 mol.%), Yb3+ (X%):YF3 nanoparticles. Temperature sensitivity of spectral shape is related to the phonon-assisted nature of energy transfer (PAET) between Nd3+ and Yb3+). However, in the case of single-doped Nd3+ (0.1 or 0.5 mol.%):YF3 nanoparticles, luminescence decay time (LDT) of 4F3/2 level of Nd3+ in Nd3+ (0.5 mol.%):YF3 decreases with the temperature decrease. In turn, luminescence decay time in Nd3+ (0.1 mol.%):YF3 sample remains constant. It was proposed, that at 0.5 mol.% the cross-relaxation (CR) between Nd3+ ions takes place in contradistinction from 0.1 mol.% Nd3+ concentration. The decrease of LDT with temperature is explained by the decrease of distances between Nd3+ with temperature that leads to the increase of cross-relaxation efficiency. It was suggested, that the presence of both CR and PAET processes in the studied system (Nd3+ (0.5 mol.%), Yb3+ (X%):YF3) nanoparticles provides higher temperature sensitivity compared to the systems having one process (Nd3+ (0.1 mol.%), Yb3+ (X%):YF3). The experimental results confirmed this suggestion. The maximum relative temperature sensitivity was 0.9%·K−1 at 80 K.

This article shows the success of using the chemical reduction method, the polyol thermolytic process, the sonochemistry method, and the hybrid sonochemistry/polyol process method to design iron-based magnetically active composite nanomaterials in a hyperbranched polyester polyol matrix. Four samples were obtained and characterized by transmission and scanning electron microscopy, infrared spectroscopy and thermogravimetry. In all cases, the hyperbranched polymer is an excellent stabilizer of the iron and iron oxides nanophase. In addition, during the thermolytic process and hybrid method, the branched polyol exhibits the properties of a good reducing agent. The use of various approaches to the synthesis of iron nanoparticles in a branched polyester polyol matrix makes it possible to control the composition, geometry, dispersity, and size of the iron-based nanophase and to create new promising materials with colloidal stability, low hemolytic activity, and good magnetic properties. The NMR relaxation method proved the possibility of using the obtained composites as tomographic probes.