One-phonon Raman spectra of carbon in composite films prepared by modification of amorphous hydrogenated carbon by copper and cobalt

One-phonon visible-range Raman spectra of a-C: H〈Cu〉 and a-C: H〈Co〉 composite films with comparable metal and carbon contents were studied in the frequency region 1200–1700 cm^?1 including the carbon sp²-bond vibrations. Broad bands G and D characteristic of unmodified a-C: H films, as well as some additional features, are observed experimentally in the spectra. By unfolding the spectra into Gaussian components, it was possible to follow the variation of Raman shifts and of contributions of individual components to the spectrum as a function of metal content and thermal annealing. The data obtained, complemented by available information on carbon sp²-coordinated systems, show that incorporation of Cu or Co favors growth and ordering of graphite-like nanoclusters in a-C: H, the effect being substantially stronger in the case of Co. It is shown that the process of metal-stimulated graphitization includes carbon bond breaking with the formation of short chainlike fragments and their linkage with the formation of aromatic-ring nanoclusters. A qualitatively similar sp²-structure rearrangement takes place under thermal annealing. For the Cu and Co concentrations studied, the linear dimensions L _a of graphite-like clusters are estimated to vary from ～0.8 nm in unannealed a-C: H to ～1.0 and ～1.2 nm in annealed a-C: H〈Cu〉 and a-C: H〈Co〉, respectively. The number of aromatic rings in these clusters is approximately estimated to increase from 12 to 16 (for Cu) and 20 (for Co).     

EPR and photoluminescence spectra of smooth CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films from T-10 tokamak: The effect of iron impurity

The electron and spin structure of thick smooth hydrocarbon CD _x films (“flakes”) with a high relative deuterium concentration of x ~ 0.5, redeposited from deuterium plasma discharge onto the walls of the vacuum chamber of the T-10 tokamak and containing ~1 at % of 3d-metal impurities due to erosion of the chamber walls, are studied using electron paramagnetic resonance (EPR) and photoluminescence (PL). The resulting spectra are compared for the first time to the EPR and photoluminescence spectra of polymer (soft) a-C:H(D) films (H(D)/C ~ 0.5), which are considered model analogues of smooth CD _x films. A certain similarity of the CD _x films with a-C:H films was found in the electronic structure of the valence band. At the same time, the differences in the EPR and photoluminescence spectra were observed due to the presence of 3d-metal impurities in the CD _x samples, contributing to the conversion of sp ³ → sp ² in the formation of films in the tokamak and upon heating and thermal desorption. An impurity of, presumably, 3d metals was detected for the first time by EPR in the a-C:H films in an amount of approximately 0.2 ppm, related to the evaporation of graphite.     

Structure and phase composition of thin a-C:H films modified by Ag and Ti

The structure and phase composition of thin a-C:H and a-C:H〈M〉 films (M = Ag, Ti, or Ag + Ti) have been studied by Raman and X-ray photoelectron spectroscopy. The a-C:H〈M〉 films were prepared by ion-plasma magnetron sputtering of a combined target of graphite and metal in an Ar–CH₄ gas mixture. The Raman spectra of these films indicate that their structure is amorphous. The a-C:H〈Ag + Ti〉 films have a more graphitized structure in comparison with pure a-C:H films and films containing only one metal. It is established that carbon in the a-C:H〈Ag + Ti〉 films is in the sp ², sp ³, and C=O states, which are characteristic of the a-C:H, a-C:H〈Ag〉, and a-C:H〈Ti〉 films. In addition, there are also ether (–C–O–C–) or epoxy (?C?O–) carbon groups in the a-C:H〈Ag + Ti〉 films. It has been revealed that silver atoms in the a-C:H〈Ag〉 and a-C:H〈Ag + Ti〉 films form no chemical bonds with carbon, oxygen, and titanium. Titanium in the a-C:H〈Ti〉 and a-C:H〈Ag + Ti〉 films exists in the form of titanium IV oxide (TiO₂).     

The effect of alloying on the structure and peculiarities of tribological behavior of vacuum-deposited diamond-like coatings

In this work, we report the results of a study of the atomic and crystalline structures, phase and chemical compositions and tribological properties of DLC coatings deposited by plasma-assisted (PA) CVD (a-C:H:Si and a-C:H:Si:Mo) and magnetron reactive sputtering (a-C:H:Cr). The a-C:H:Si:Mo coatings revealed the formation of ultra-dispersed inclusions of either molybdenum carbides or silicides, whereas no such inclusions were found in the a-C:H:Si compound. The a-C:H:Cr coatings that were deposited in an acetylene–nitrogen gas mixture exhibited a nanocomposite structure composed of chromium, its carbide and nitride phases. The tribological tests showed that the DLC coatings with silicon and silicon–molybdenum have a high friction coefficient and a low working performance, while the chromium-containing coatings have high levels of their mechanical and tribological characteristics, making them promising materials for operation under high contact pressures.     

Properties of nanogranular metal-dielectric composites in strong electric fields and the cluster electronic states

The electrical resistance of granular structures with ferromagnetic and nonferromagnetic metal nanoparticles embedded in concentrations below the percolation threshold was studied in strong electric fields. More specifically, amorphous silicon dioxide containing nanoparticles of a Co₄₁Fe₃₉B₂₀ alloy [(a-SiO₂)_{100? x}(Co₄₁Fe₃₉B₂₀)_x structure] and amorphous hydrogenated carbon with embedded copper nanoparticles, a-C: H(Cu), were investigated. The (a-SiO₂)_100?x(Co₄₁Fe₃₉B₂₀)_x structures revealed changes in the electrical resistance and magnetoresistance after being subjected to a strong electric field. The changes could have reversible or irreversible character and depended on the electrical prehistory of the sample. A strong electric field caused not only a decrease in the electrical resistance but also a decrease in the magnetoresistance, although the magnetization of the sample remained unchanged. The temperature dependences of the current in a-C: H(Cu) films exhibited conductivity peaks under a decrease in temperature in strong electric fields and transitions from the insulating to conducting state; after the field was removed, there occurred reverse transitions and conductivity relaxation, as well as pronounced changes in the dielectric permittivity and an increase in dielectric losses with increasing temperature. A model of cluster electronic states (CESs) is proposed to account for the experimental findings. These states are created by electrons of the metal grains and matrix defects near the Fermi surface. The observed features find explanation in a change in the CES structure. A strong electric field does not bring about d-electron delocalization, and the fraction of d electron wave functions in a CES is small.     

Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon (c-Si) using Ge⁺ (40 keV/1 × 10¹⁷ ions/cm²) and Ag⁺ (30 keV/1.5 × 10¹⁷ ions/cm²) ions and sequential irradiation using Ge⁺ and Ag⁺ ions is presented. The implantation of the Ge⁺ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20–40 nm. The implantation of c-Si using Ag⁺ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag⁺ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220–420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.     

Surface structural,morphological, and catalytic studies of homogeneously dispersed anisotropic Ag nanostructures within mesoporous silica

Highly dispersed anisotropic Ag nanostructures were synthesized within the channels of 3-aminopropyltrimethoxysilane (APTMS)-modified mesoporous SBA-15 for catalyzing the reduction of p-dinitrobenzene, p-nitrophenol, and p-nitroacetophenone, respectively. A green templating process without involving any reducing agent, by varying the amount (1–10 wt.%) of Ag loading followed by calcination at 350 °C under H₂ led to change in the morphology of Ag nanoparticles from nanospheres (~7–8 nm) to nanorods (aspect ratio ~12–30 nm) without any deformation in mesoporous sieves. In comparison to white bare SBA-15, gray-colored samples were formed with Ag impregnation exhibiting absorption bands at 484 and 840 nm indicating the formation of anisotropic Ag nanostructures within mesoporous matrix. TEM and FE-SEM micrographs confirmed the presence of evenly dispersed Ag nanostructures within as well as on the surface of mesoporous matrix. AFM studies indicated a small decrease in the average roughness of SBA-15 from 20.59 to 19.21 nm for 4 wt.% Ag/m-SBA-15, illustrating the encapsulation of majority of Ag nanoparticles in the siliceous matrix and presence of small amount of Ag nanoparticles on the mesoporous support. Moreover, due to plugging of mesopores with Ag, a significant decrease in surface area from 680 m²/g of SBA-15 to 385 m²/g was observed. The Ag-impregnated SBA-15 catalyst displayed superior catalytic activity than did bare SBA-15 with 4 wt.% Ag-loaded catalyst exhibiting optimum activity for selective reduction of p-nitrophenol to p-aminophenol (100 %), p-nitroacetophenone to p-aminoacetophenone (100 %), and p-dinitrobenzene to p-nitroaniline (87 %), with a small amount of p-phenylenediamine formation.

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Graphical abstract This paper demonstrates the spontaneous formation of uniformly dispersed Ag nanospecies of various morphologies (nanospheres, size ~7–8 nm and nanorods, aspect ratio ~12–30 nm), both within as well as on the surface of the mesoporous SBA-15, as a function of increased Ag loading. Surface structural and other physiochemical properties of Ag/m-SBA-15 nanocomposites were considerably influenced w.r.t change in Ag loading. Ag/m-SBA-15 nanocomposites with 4 wt.% Ag loading exhibited the highest selectivity (87 %) for the selective reduction of p-dinitrobenzene to p-nitroaniline and 100 % selectivity for p-nitrophenol to p-aminophenol and p-nitroacetophenone to p-aminoacetophenone, respectively.

     

The effect of the size,shape, and structure of metal nanoparticles on the dependence of their optical properties on the refractive index of a disperse medium

The effect of the size, shape, and structure of gold and silver nanoparticles on the dependence of their extinction and integral scattering spectra on the dielectric environment has been investigated. Calculations were performed using the Mie theory for spheres and nanoshells and the T-matrix method for chaotically oriented bispheres, spheroids, and s cylinders with hemispherical ends. The sensitivity of plasmon resonances to variations in the refractive index of the environment in the range 1.3–1.7 for particles of different equivolume size, as well as to variations in the thickness of the metal layer of nanoshells, was studied. For nanoparticles with an equivolume diameter of 15 nm, the maximal shifts of plasmon resonances due to variation in the refractive index of the environment are observed for bispheres and the shifts decrease in the series nanoshells, s cylinders or spheroids, and spheres. For particles 60 nm in diameter, the largest shifts of plasmon resonances occur for nanoshells and the shifts decrease in the series bispheres, s cylinders or spheroids, and spheres. All other conditions being the same, silver nanoparticles are more sensitive to the resonance tuning due to a change in the dielectric environment.     

Evolution of surface morphology during the growth of amorphous and polycrystalline silicon films

The evolution of the surface morphology of LPCVD poly-Si films (deposition temperature 620°C), a-Si films (deposition temperature 550°C) and poly-Si films, obtained by the crystallization of a-Si is investigated in the thickness range 40–500 nm. It is found that upon an increase in the thickness from 40 to 500 nm, the surface roughness (parameters S _q , S _z , S _v ) is increased for poly-Si, while in the case of a-Si and poly-Si obtained by crystallization a-Si, on the contrary, decreases. The correlation length (S _al ) increases for all three types of silicon films. Poly-Si films, obtained by the crystallization of a-Si, as compared to LPCVD poly-Si films have a significantly lower surface roughness, respectively, S _q two times less at a thickness of 40 nm and sixteen times less at 500 nm. In contrast to thick films, thin a-Si films (at thicknesses of less than 40 nm) have a granular structure, which is especially pronounced at an average thickness of about 20 nm and there is a maximum on the dependence of the roughness S _q on the thickness.     

Evaluation of spectral dispersion of optical constants of a-Se films from their normal-incidence transmittance spectra using Swanepoel algebraic envelope approach

Spectral dispersions of index of refraction \({n(\lambda )}\) and extinction coefficient \({\kappa (\lambda )}\) of undoped amorphous selenium (a-Se) films of three thicknesses (d?≈?0.5, 0.75, and 1.0 µm) were evaluated by analyzing experimental room-temperature normal-incidence transmittance-wavelength (\({{T_{{\text{exp}}}}(\lambda )} - \lambda\)) data (λ =?400–1100 µm) of their air-supported {a-Se film/thick glass slide}-stacks using Swanepoel’s transmission envelope theory of uniform films. Above a wavelength \({{\lambda _c}\,\, \approx \,\,640\;{\text{nm}}}\), as-measured \({{T_{{\text{exp}}}}(\lambda )}\,\, - \,\lambda\) spectra display well-resolved maxima and minima, with minor shrinkage in transparent and weak absorption regions (750–1100 nm). Below \({\lambda _{\text{c}}}\), a smeared sharp decline of \({{T_{{\text{exp}}}}(\lambda )}\) with decreasing λ, signifying strong absorption in a-Se films and existence of band-tail localized states. For λ > λ _c, the \({n\,(\lambda )}\, - \,\lambda\) data retrieved from algebraic envelope procedures followed a Sellmeier-like dispersion relation, with the best-fit values of high-frequency dielectric constant \({{\varepsilon _\infty }\, \approx \,\,{\text{4.9}}}\), static index of refraction \({{n_{\text{0}}} = n\left( {E\, \to \,{\text{0}}} \right)\,\, \approx \,\,{\text{2.43}}}\), and resonance wavelength \({{\lambda _0}\, \approx \,490\,\,{\text{nm}}}\), which may be assigned to onset of photogeneration in a-Se. Urbach-like dependency of absorption coefficient \({\alpha (h{{\nu }})}\) of a-Se films on photon energy \({h{{\nu }}}\) was realized with an Urbach-tail breadth of 85 meV. All achieved optical parameters were found to be slightly dependent on film thickness. Findings of present algebraic analysis are consistent with reported literature results obtained on the basis of other optical analytical approaches.     

Amplitude-phase reflectance spectra of amorphous silicon-based Bragg structures

Amplitude-phase spectra of light reflection from distributed Bragg reflectors and Fabry-Pérot microcavities based on a-Si: H/a-SiO_x: H thin films have been studied. The frequency dependence of the phase difference between the amplitude p-and s-light reflection coefficients within the photonic band gap is measured. The phase spectrum exhibits predominantly a monotonic, close-to-linear frequency behavior, except for spectral regions near the stop band edges and near the singularities related to the microcavity eigenmodes. The experimental spectra are compared with theoretical calculations based on the transfer matrix method and approximate analytical relations. A method based on analyzing amplitude-phase reflectance spectra is proposed for structural characterization of multilayer microcavity systems.     

Synthesis,characterization and third-order nonlinear optical properties of polydiacetylene nanostructures,silver nanoparticles and polydiacetylene–silver nanocomposites

We have synthesized, characterized and studied the third-order nonlinear optical properties of two different nanostructures of polydiacetylene (PDA), PDA nanocrystals and PDA nanovesicles, along with silver nanoparticles-decorated PDA nanovesicles. The second molecular hyperpolarizability γ(?ω; ω, ?ω, ω) of the samples has been investigated by antiresonant ring interferometric nonlinear spectroscopic (ARINS) technique using femtosecond mode-locked Ti:sapphire laser in the spectral range of 720–820 nm. The observed spectral dispersion of γ has been explained in the framework of three-essential states model and a correlation between the electronic structure and optical nonlinearity of the samples has been established. The energy of two-photon state, transition dipole moments and linewidth of the transitions have been estimated. We have observed that the nonlinear optical properties of PDA nanocrystals and nanovesicles are different because of the influence of chain coupling effects facilitated by the chain packing geometry of the monomers. On the other hand, our investigation reveals that the spectral dispersion characteristic of γ for silver nanoparticles-coated PDA nanovesicles is qualitatively similar to that observed for the uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the γ values of the coated nanovesicles slightly as compared to that of the uncoated nanovesicles, suggesting a definite but weak coupling between the free electrons of the metal nanoparticles and π electrons of the polymer in the composite system. Our comparative studies show that the arrangement of polymer chains in polydiacetylene nanocrystals is more favourable for higher nonlinearity.     

Effect of the chemical state of silver on the luminescence properties of GeO<Subscript>2</Subscript>-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ag films

A sol-gel method is used to prepare GeO₂-Eu₂O₃-Ag films in which the luminescence efficiency of Eu³⁺ ions during UV excitation is comparable to that in films activated by organic europium complexes. The luminescence spectra of these films are recorded, and the films are also studied using EPR and x-ray diffraction. The main origin of this effect is found to be complex Eu-Ag centers with a high quantum yield of the intracenter transfer of excitations to the rare-earth activator from silver ions and Ag _m ⁿ⁺ oligomer clusters located on the surface of silver nanoparticles.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

The Structure of Radiative Tunnel Recombination Sites in Emulsion Microcrystals of AgBr(I)

To identify the structure of emissive tunnel recombination sites in the emulsion microcrystals of silver bromide AgBr(I) with iodine contaminations and to determine the role of an emulsion medium in their formation, the temperature dependence of the luminescence spectra in the range from 77 to 120 K, the kinetics of the growth of the maximum luminescence intensity value at λ ≈ 560 nm, and the luminescence flash spectrum stimulated by the infrared light are investigated. Two types of the AgBr_{1 – x}(I _x ) (x = 0.03) microcrystals—namely, obtained in an aqueous solution and on a gelatin substrate—are used in the studies. It is established that the emissive tunnel recombination sites with a luminescence maximum at λ ≈ 560 nm in AgBr_{1 – x}(I _x ) (x = 0.03) are the {(I _a ^- I _a ^- )Ag _i ⁺ } donor–acceptor complexes with the I _a ^- iodine ions located in neighbor anionic sites of the AgBr(I) crystal lattice, next to which the Ag _i ⁺ interstitial silver ion is positioned. With an increase in the temperature, the {(I _a ^- I _a ^- )Ag _i ⁺ } sites undergo structural transformation into the {(I _a ^- I _a ^- )Ag_in⁺} sites, where n = 2, 3, …. Moreover, the {(I _a ^- I _a ^- )Ag _in ⁺ } sites (n = 2) after the capture of an electron and hole also provide the tunnel recombination with a luminescence maximum at λ ≈ 720 nm. The influence of an emulsion medium consists in that gelatin interacts with the surface electron-localization sites, i.e., the interstitial silver ions Ag _in ⁺ , n = 1, 2, and forms the complexes {Ag _in ⁰ G⁺} (n = 1, 2) with them. The latter are deeper electron traps with a small capture cross section as compared to the Ag _in ⁺ sites (n = 1, 2) and that manifest themselves in that the kinetics of the luminescence growth in AgBr(I) to a stationary level at λ ≈ 560 nm is characterized by the presence of “flash firing.” At the same time, the luminescence flash stimulated by IR light, for which the Ag _in ⁺ (n = 1, 2) electron-localization sites are responsible, is absent. It is supposed that the electrons localized on the {Ag _in ⁺ G⁺} complexes (n = 2) retain the capability for emissive tunnel recombination with holes localized on paired iodine sites with a luminescence maximum at λ ≈ 750 nm.     

Superconductor-insulator transition tuned by annealing in Bi-film on top of Co-clusters

We deposited amorphous Bi films with a thickness between 3 and 6.5 nm at 4.2 K on top of previously deposited Co clusters having a mean size of ～4.5 nm. The Co cluster layers thickness was between 2.3 and 5 nm. In-situ electrical transport measurements were performed between 2 and 100 K. Measurements on as-prepared samples having a Bi layer thickness of 3.0 nm show hopping (tunneling) conductivity as σ(T) = σ ₀ exp[?(T ₀/T)^1/2] above the superconducting transition temperature T _C and re-entrance behavior again with hopping (tunneling) conductivity below T _C . Annealing of films having a Bi layer thickness of 5.5 nm results in a decrease of resistivity, with variable-range hopping conduction behavior as σ(T) = σ ₀ exp[?(T ₀/T)^1/3 ]. Quite different are the findings for films having a Bi layer thickness of 6.5 nm: annealing of these films results in a power-law behavior as σ(T) = σ ₀ T ^α with α = 2/3, indicating that these films are close to a quantum critical point separating superconducting and insulating phases. A phase diagram including all experimental observations is proposed.     

Amplitudes and phases of electron scattering in polyatomic systems for the structural analysis of disordered,amorphous, and nanosized materials via EXAFS spectroscopy

The results from developing and testing a software package for calculating the amplitudes and phases of electron scattering in polyatomic systems are presented. The potential with which an excited electron moves in a medium is constructed using the muffin-tin approximation with Hartree–Fock exchange interaction. Tests of the package for metals, oxides, and iron-bearing water sulphate solutions show that structural parameters can be derived with high degrees of accuracy (the error for interatomic distances is ~0.01 Å; for coordination numbers, it is ~7%). Using the developed approach and software, analysis of the Ag K-EXAFS spectra of silver nanoparticles in silica glass allow us to determine the average structural parameters of Ag–O and Ag–Ag bonds.     

Optical and electrical properties of thin NiO films deposited by reactive magnetron sputtering and spray pyrolysis

Thin NiO films are deposited by reactive magnetron sputtering and spray pyrolysis. The main optical constants, i.e., refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ), and thickness d, are determined. The temperature dependence of the resistance of thin films is found, and the activation energy of films deposited by different methods is determined.     

Berechnung des Magnetisierungs-„Ripple“ in ferromagnetischen dünnen Schichten

By means of straight forward analysis a complete calculation is given of magnetization ripple in polycrystalline ferromagnetic films. Wavelenghts and practical relations for ripple amplitude, length of coherence, and angle fluctuation are derived (which were so far only rather incompletely available from a very rough model of the ripple, given previously by the author). The dependence of ripple wavelength (λ ₀) on average crystallite sizea reaches a plateau at a definite critical valuea=a _g ∶λ ₀≈4a fora<a _g ,λ ₀ independent ofa fora>a _g , as has been found most recently byBaltz andDoyle.     

Ferrimagnetic nanoparticles for self-controlled magnetic hyperthermia

Based on the Heisenberg model including single-site uniaxial anisotropy and using aGreen’s function technique we studied the influence of size and composition effects on theCurie temperature T _C , saturationmagnetization M _S and coercivityH _C of spherical nanoparticles with astructural formulaM e _1?x Zn _x Fe₂O₄,Me = Ni, Cu, Co, Mn. It is shown that for x = 0.4–0.5and d = 10–20 nm these nanoparticles have aT _C  = 315 K and are suitable for aself-controlled magnetic hyperthermia.