[en] High-quality single-layer and bilayer diamond-like carbon (DLC) thin films are fabricated by two technologies, namely, ion-assisted plasma-enhanced deposition (IAPED) and electron cyclotron resonance (ECR) deposition. Deposition on various substrates, such as sapphires and solar cells, has been performed at low substrate temperatures (50 ∼ 80 C). The two deposition technologies allow good control over the growth conditions to produce DLC films with desired optical properties, thickness, and energy bandgap. The bilayer-structured DLC can be fabricated by using IAPED for the bottom layer followed by ECR for the top layer, or just by IAPED for both layers with different compositions. The DLC films have shown good spatial uniformity, density, microhardness, and adhesion strength. They exhibit excellent stability against attack by strong acids, prolonged damp-heat exposure at 85 C and 85% relative humidity, mechanical scratch, ultrasonication, and irradiation by ultraviolet (UV), protons, and electrons. When deposited on crystalline Si and GaAs solar cells in single-layer and/or bilayer structure, the DLC films not only serve as antireflection coating and protective encapsulant, but also improve the cell efficiencies

[en] The magnetic structure of the Sr₂Cu₃O₄Cl₂ two-subsystem antiferromagnet is studied by the nuclear quadrupole resonance (NQR) method on the ^63,65Cu and ³⁵Cl nuclei. The resonance spectrum above T_N2 = 40 K is determined by the Zeeman splitting of the levels of the ^63,65Cu nuclei of the copper atoms at the Cu1 site with the first-order quadrupole perturbation. The magnetic field on the copper nuclei is equal to 93 kOe. The spectrum below n is significantly different: it includes a low-frequency part, which is associated with the ordering of the second magnetic subsystem Cu2. The splitting of the NQR lines of ³⁵Cl is observed above and below T_N2. This fact indicates the ferromagnetic ordering of the moments of the Cu1 subsystem, which are located along the c axis of the crystal, and makes it possible to determine the direction of the magnetic field on Cu1 copper as (110)

[en] The results of the measurements of the ^6,7Li and ²³Na nuclear magnetic resonance (NMR) and ^63,65Cu nuclear quadrupole resonance in LiCu₂O₂ and NaCu₂O₂ quasi-one-dimensional compounds with a spin chains in the paramagnetic and magnetically ordered states are presented. The shape of the NMR line below T_c = 24 and 13 K for LiCu₂O₂ and NaCu₂O₂, respectively, is characteristic of the incommensurate static modulation of the local magnetic field matching with the incommensurate spiral modulation of the magnetic moments. The differences in the shape of the NMR spectra of ²³Na and ⁷Li are discussed in terms of the features of the crystal structure of LiCu₂O₂ and NaCu₂O₂

[en] A comparative magnetic resonance study on correlated semiconductors is presented. Nuclear spin-lattice relaxation measurements provide an excellent method to gain local information about the gap formation in this new class of materials. In contrast to U2Ru2Sn (Δ/k_B ∼ 230 K) in CeRu₄Sn₆ the gap is slightly reduced (Δ/k_B ∼ 200 K) and correlations form out of a residual density of states in the gap. For FeSb₂ there is revived interest after classifying this system as the second Fe containing Kondo insulator beside FeSi. Surprisingly, FeSb₂ shows a colossal Seebeck coefficient at low temperatures. Using ^121,123Sb nuclei as a local probe, our NMR/NQR investigations strongly support the gap scenario. The spin-lattice relaxation rate ¹²³(1/T₁) in the entire investigated temperature range 2-200 K is perfectly fitted with rectangle DOS model with narrow impurity in-gap band. These in-gap states might originate the high thermopower observed. The obtained gap value is (Δ/k_B ∼ 473 K).

No abstract available

[en] Local magnetic fields H_loc exceeding significantly the magnetic fields produced by nuclear magnetic moments (a few gauss) have been detected in bismuth compounds with valence s and p electrons, which are generally believed to be diamagnetic, by the methods based on measuring the parameters of nuclear quadrupole interactions. Anomalies in the magnetic properties of BiSbO₄ and Bi₄Si₃O₁₂ were clearly manifested when analyzing the line shapes in their ²⁰⁹Bi NQR spectra. The quartet of lines for the lower transition ν₁ (Δm = 1/2–3/2) in the spectrum of Bi₄Si₃O₁₂ in zero external magnetic field and the doublets for the lines of all other transitions in the spectrum of BiSbO₄ at unique crystallographic positions of bismuth atoms in the crystal lattices of the compounds suggest a magnetic nature of the splittings. The most probable values of H_loc in these compounds are those in the range from 40 to 100 G.

[en] An NMR analysis of ³¹P nuclei in metallic iron phosphide FeP has been performed both in a zero field and by sweeping the external magnetic field at several fixed frequencies with the aim of revealing and investigating the transformation of the magnetic helical structure of FeP. The NMR lineshape gradually changes with an increase in the field strength from trapezoidal (in weak fields) to pronounced asymmetric with two peaks (in strong fields). The former shape is typical of NMR spectra of powder samples under an applied magnetic field, while the latter is characteristic of NMR spectra of nonmagnetic atoms in single-crystalline helimagnetics. The observed transformation of the FeP NMR spectrum evidences in favor of the spin-reorientation transition of a spin-flop type in FeP at strong external fields.

[en] The magnetic properties of LiCu₂O₂ single-crystal samples without twinning are investigated using electron spin resonance and nuclear magnetic resonance spectroscopy. The experimental results obtained are described in terms of the model of a planar spiral antiferromagnet for the orientation of the magnetic field H -parallel b or H -parallel c and the model of a collinear spin-modulated antiferromagnet for the orientation of the static magnetic field H -parallel a

[en] ^121,123Sb nuclear quadrupole resonance (NQR) was applied to Fe(Sb_1-xTe_x)₂ in the low doping regime (x = 0 , 0.01, and 0.05) as a microscopic zero field probe to study the evolution of 3d magnetism and the emergence of metallic behavior. Whereas the NQR spectra itself reflects the degree of local disorder via the width of the individual NQR lines, the spin lattice relaxation rate (SLRR) 1/T₁ (T) probes the fluctuations at the Sb site. The fluctuations originate either from conduction electrons or from magnetic moments. In contrast to the semimetal FeSb₂ with a clear signature of the charge and spin gap formation in 1/T₁(T)T[~exp/(Δk_BT)] , the 1% Te-doped system exhibits almost metallic conductivity and the SLRR nicely confirms that the gap is almost filled. A weak divergence of the SLRR coefficient 1/T₁(T)T ~ T^-n ~ T^-0.2 points towards the presence of electronic correlations towards low temperatures. This is supported by the electronic specific heat coefficient γ = (C_el/T) showing a power-law divergence γ (T) ~ T^-m ~ (1/T₁T)^1/2 ~ T^-n/2 ~ C_el/T which is expected in the renormalized Landau Fermi liquid theory for correlated electrons. In contrast to that the 5% Te-doped sample exhibits a much larger divergence in the SLRR coefficient showing 1/T₁(T)T ~ T^-0.72 . According to the specific heat divergence a power law with n = 2 m = 0.56 is expected for the SLRR. This dissimilarity originates from admixed critical magnetic fluctuations in the vicinity of antiferromagnetic long range order with 1/T₁(T)T ~ T^-3/4 behavior. Furthermore Te-doped FeSb₂ as a disordered paramagnetic metal might be a platform for the electronic Griffith phase scenario. NQR evidences a substantial asymmetric broadening of the ^121,123Sb NQR spectrum for the 5% sample. Lastly, this has a predominant electronic origin in agreement with the electronic Griffith phase and stems probably from an enhanced Sb-Te bond polarization and electronic density shift towards the Te atom inside Sb-Te dumbbell.

[en] The results are presented of experimental and theoretical study of the phenomenon of secondary nuclear spin echo in magnetically ordered materials in which the formation of additional echo signals is due to dynamic hyperfine coupling. Numerical simulation of the effect of the amplitude (ω₁) and the durations of the first (t₁) and the second (t₂) exciting pulses on the echo signals is performed. It is found that the maximum amplitude of the secondary echo is formed under the conditions ω₁t₁ = 0.5π and ω₁t₂ ≈ 0.6π. It is shown that secondary echo signals can be observed upon inhomogeneous excitation of the spectral line ω₁ ≤ Δω, where Δω is the inhomogeneous spectral line width. At a temperature of T = 4.2 K, additional double-pulse spin 3τ-echo signals from iron nuclei are experimentally observed in an epitaxial yttrium ferrite garnet film enriched with ⁵⁷Fe magnetic isotope to 96%. The experimentally observed phase relationships between the primary and secondary echo signals, as well as the dependence of the echo signal amplitude on the amplitude and duration of the exciting pulses, are in good agreement with the results of numerical simulation of the dynamics of nuclear magnetization with regard to the dynamic hyperfine coupling. It is shown that the secondary echo exhibits the effect of spectral line narrowing, and the amplitude of the secondary echo is proportional to the nuclear magnetic resonance (NMR) enhancement factor in magnets, η. In the case of ⁵⁷Fe NMR in an yttrium iron garnet (YIG) film, the amplitude of the 3τ-echo is two to three orders of magnitude smaller than the amplitude of the primary 2τ-echo, which corresponds to η ≈ 440. The detection of weak secondary echo signals proves to be possible due to the use of a phase-coherent NMR spectrometer with digital quadrature detection at the carrier frequency and signal accumulation.