Observation of electric quadrupole spin resonance of Ho<Superscript>3+</Superscript> impurity ions in synthetic forsterite

The anomalous dependence of the electron paramagnetic resonance (EPR) line shape on the microwave power in the resonator has been found when studying the continuous-wave EPR spectra of impurity holmium ions in synthetic forsterite on an ELEXSYS E 580 EPR spectrometer. The power-threshold transition from the conventional lines being the derivatives of the spectral line contours to the spectral line contours themselves has been observed as the power increased. The properties of the anomalous EPR lines are qualitatively explained assuming that the resonance electric quadrupole transitions take place between the electron spin levels.     

Synthesis and spectroscopic properties of LiIn(WO4)2 nanopowders and single crystals doped with chromium(III) ions

LiIn(WO₄)₂ single crystals and nanopowders doped with chromium(III) ions were synthesized and investigated, including their EPR spectra and magnetic properties. The EPR spectra have shown low and high field lines attributed to isolated chromium ions with an electron spin S=3/2 and complex chromium centers with higher spin value, respectively. Magnetic susceptibility measurements revealed an almost linear dependence on the magnetic field. The electron resonance and magnetic properties have been related to the structural and spectroscopic data of the studied material.     

Low-temperature heat capacity of rare-earth tetraborides

The paper reports an experimental study of the temperature dependences of the heat capacity of tetraborides of lanthanum, dysprosium, holmium, and lutetium in the range 2–300 K. The electronic, lattice, and magnetic contributions to the total heat capacity of the borides have been identified and analyzed, and the Schottky contribution has been calculated. The ground-state multiplicities of dysprosium and holmium ions in the tetraborides have been determined.     

On reasons for the hysteresis of melting and crystallization of nanoparticles

The specific features of the EPR spectra of Tm³⁺ impurity ions in synthetic forsterite have been studied by continuous-wave EPR spectroscopy in the frequency range of 270–310 GHz at a temperature of 4.2 K in weak magnetic fields. Narrow resonance signals unrelated to the modulation of the resonance conditions of EPR under the modulation of the external magnetic field have been discovered in measurements at frequencies corresponding to the zero field splitting between the ground and first excited singlet electron states of Tm³⁺ ions in zero magnetic field. The origin of these narrow lines is discussed.     

Geometrical resonance of the Rayleigh sound wave absorption as a method for direct measurements of the electron specular reflection coefficient from the metal surface

A theory of resonant absorption of the Rayleigh sound waves in metals has been developed for the case of weak magnetic fields (i.e. the Pippard type geometrical oscillations). The amplitude and shape of resonance lines have been studied in relation to the nature of electron reflection from the surface. It has been shown that observations of the geometrical resonance oscillations may serve for investigating directly surface reflectivity of the metal with respect to conduction electrons.     

Mobility of magnetic helicoid in holmium nano-layer

Spin valves with holmium layers and three-layer structures metal/Ho/metal were prepared by magnetron sputtering. A holmium layer in the spin valves is polycrystalline with weak axial <002> texture. The structural coherence length along the hexagonal c-axis is approximately 2/5 of the total thickness of the holmium layer. Field dependences of the spin valves magnetoresistance were measured at different temperatures. Correlation was revealed between magnetic state in holmium layer and the shape of magnetoresistive curve. Deviation of magnetic moments of the reference layer and the adjacent part of holmium from the applied magnetic field was investigated. The field induced mobility of the magnetic helicoid in holmium layers was revealed.     

Spherulitic crystallization of holmium tartrates in silica gels

Spherulites of holmium tartrate trihydrate and holmium nitro-tartrate monohydrate have been grown in silica gel medium by making holmium nitrate to react with tartaric acid at high supersaturations. The mechanism of spherulitic growth of holmium tartrates is discussed. The spherulitic crystallization is shown to be due to heterogeneous nucleation. In the early stages of growth an amorphous spherical mass gets nucleated inside the gel. Crystal fibers diverge radially from the surface of the spherical mass giving rise to a spherical polycrystalline holmium tartrate. Thermal stability of the two types of spherulites grown in the silica gel shows that the holmium tartrate trihydrate is more stable than holmium nitro-tartrate monohydrate. The surface morphology and internal structure of the spherulites of holmium tartrates have been studied by using scanning electron microscopy. The results on growth kinetics are given by studying the variation of radius of spherulites as a function of time. A non-linear time–size relations under several conditions of growth have been observed, which suggests a non-uniform solute concentration at the crystal surface.     

Mesoscopic conductance fluctuations of a two-dimensional electron gas in a one-dimensional lattice of antidots

Mesoscopic conductance fluctuations of a two-dimensional electron gas in a one-dimensional periodic array of antidots have been studied experimentally, for the first time. The fluctuations show a quasiperiodic behaviour on magnetic field, with period corresponding to the quantization of magnetic flux through the area of a unit cell of the one-dimensional array. The existence of the quasiperiodic component is explained by an anomalous area distribution of interfering trajectories.     

The absorption of rayleigh's sound waves in metals in a parallel magnetic field

The electron absorption coefficient has been calculated for the Rayleigh waves in a metal, with the magnetic field parallel to the boundary. Reflection of electrons from the metal surface is assumed to diffuse. For high magnetic fields the shape and width of the absorption lines have been investigated as well as maximum values of the attenuation. For low fields oscillations of the geometric and cyclotron resonance type are predicted.     

Ultrasonic identification of a new spin-ordering phase transition in holmium

A new tilted spiral phase has been identified in holmium by associating it with an anomalous peak in the shear wave attenuation at 24°K. When a magnetic field is applied in the basal plane the peak moves up in temperature; when it is applied parallel to the c-axis the peak moves down. We propose a model which predicts the observed experimental results.     

Improving the electrong-2 measurement

The measurement and calculation of the anomalous magnetic moment of the electron currently provides the most stringent test of QED. In the past, one of the limitations in the experiment has been the small inhomogeneous component of the magnetic field which has been used to detect the magnet resonances of the trapped electron. We have developed a technique which allows us to reduce this inhomogeneous field by as much as two orders of magnitude and have demonstrated the technique with a factor of fifteen reduction, virtually eliminating the broadening of the magnetic lines in our geonium atom.     

Paramagnetische Relaxation in Holmium- und Dysprosium-Äthylsulfat

The magneto-optical Faraday effect was used to measure the spin-lattice relaxation timeT ₁ of the rare earth ions Ho and Dy in the ethyl sulfate in the temperature range 1.4≦T≦2.15°K and for magnetic fields between 100 and 5300 oersteds. The magnetic field was pulse modulated and the approach to equilibrium in the spin populations was studied. The measured dependence ofT ₁ on the temperature is in good agreement with theory. Cross-relaxation processes have been identified in the holmium ethyl sulfate.     

Electron in a transverse harmonic cavity

Recent experiments with heavy ions and planned experiments with ultraintense lasers require nonperturbative solutions to quantum field theory for predicting and interpreting the results. To propel this theoretical direction, we solve the nonperturbative problem of an electron in a strong transverse confining potential using Hamiltonian light-front quantum field theory. We evaluate both the invariant mass spectra and the anomalous magnetic moment of the lowest state for this two-scale system. The weak external field limit of the anomalous magnetic moment agrees with the result of QED perturbation theory within the anticipated accuracy.     

A sixth order contribution to the electron anomalous magnetic moment

We evaluate analytically the contribution to the anomalous magnetic moment of the electron due to a set of sixth order graphs with two crossed photon lines. The dimensional regularization is used to parametrize the spurious infrared divergences.     

Two-dimensional electron gas in a lattice of antidots with a period of 80 nm

The magnetotransport in a two-dimensional electron gas with a lattice of antidots, which has a record-breaking small (80 nm) period and size (20–40 nm) of antidots comparable with the de Broglie wavelength of electrons, has been experimentally studied. A wide variety of new features of the magnetoresistance behavior has been observed both under semiclassical conditions and in the regime of quantizing magnetic fields. In particular, the anomalous semiclassical magnetoresistance peak induced by the nonmonotonic scattering effects has been revealed. The Shubnikov-de Haas oscillations have been revealed to exhibit an unusual transition from the anomalous period constant in the magnetic field to the normal constant in the inverse magnetic field. The effect of the generation and suppression of the oscillations has also been observed; this effect is induced by the transformation of the short and long-range scattering potentials in the lattice owing to the variation of the density of the two-dimensional electrons.     

Linewidth of ferromagnetic resonance in holmium yttrium garnet ferrites

The specific features experimentally observed in the behavior of the linewidth of ferromagnetic resonance in holmium yttrium garnet ferrites were investigated as a function of the orientation of the external magnetic field at low temperatures. The analysis was performed using the model spectrum of holmium ions, according to which the ground state of these ions is represented by two closely spaced levels (quasi-doublet) that are sufficiently far removed from the other levels. A comparison of the theoretical results with the experimental data was carried out.     

The anomalous magnetic moment of the electron in hydrogenlike ions

The precise determination of the anomalous magnetic moment of the electron bound in hydrogen-like ions allows for a stringent test of quantum electrodynamics (QED)in the presence of strong electric fields. g-factor measurements on the electron bound in hydrogen-like ions ¹²C⁵⁺ and ¹⁶O⁷⁺, using single ions confined in a Penning trap, have yielded values in agreement with theory on the ppb level. If the QED calculations are considered correct, the results can in turn be used for a determination of fundamental constants like the electron mass m_e, the fine structure constant α or nuclear parameters. We report about presentdevelopments towards g-factor measurements also in medium-heavy and heavy highly-charged ions.     

Luminescence spectra of Ho3+ in distorted parity-breaking HoF63− octahedra

Low temperature luminescence spectrum of holmium ions in monoclinic Rb₂KHoF₆ crystal was found to be well analyzable by the comparison with earlier studied cubic Cs₂NaHoF₆. The manifestation of the local symmetry influence on the strength of individual lines is found to be distinctive. In the absence of structural data, the local symmetry of holmium in Rb₂KHoF₆ is proved to be a non-centrosymmetric one. The concentration quenching of holmium luminescence in Rb₂KHoF₆ is found to be rather modest.     

On the low-threshold parametric mechanism of the anomalous power absorption in electron cyclotron resonance heating experiments in toroidal devices

The experimental conditions that facilitate the excitation of parametric decay instabilities upon the electron cyclotron resonance heating of a plasma at the second harmonic extraordinary wave in tokamaks and stellarators and, as a result, make anomalous absorption of microwave power possible have been analyzed. It has been shown that, in the case of a nonmonotonic radial profile of the plasma density, when the beam of electron cyclotron waves passes near the equatorial plane of a toroidal device, the parametric excitation of electron Bernstein waves, as well as the generation of ion Bernstein waves propagating from the parametric decay region to the nearest ion cyclotron harmonic, where they efficiently interact with ions, is possible. The proposed theoretical model can explain the anomalous generation of accelerated ions observed upon electron cyclotron heating in small and moderate toroidal facilities.     

Effects of nanocrystal shape on the physical properties of colloidal ZnO quantum dots

The effects of both nanocrystal shape and applied magnetic field on the electron energy spectra of colloidal ZnO quantum dots have been investigated in the frame of finite element method, using nonuniform triangular elements. Four shapes of quantum dots (spherical, ellipsoidal, rod-shaped, and lens-shaped) were studied. It was found that the physical properties of the semiconductor quantum dots could be manipulated by changing their size and/or their shape. The energies of an electron increase as one reduces the quantum dot shape symmetry from spherical towards the lens-shaped. The magnetic field effect strongly interplays with the nanocrystal size and the nanocrystal shape effects. Such interplay has been attributed to the competition of the quantum confinement effect introduced by the barrier potential and the quantum confinement effect introduced by the applied magnetic field.