Electron paramagnetic resonance of radiation-induced paramagnetic centers in an aerogel

Silicon oxide aerogel samples irradiated with x rays at room temperature have been analyzed using the electron paramagnetic resonance method. It has been found that three types of paramagnetic centers appear: paramagnetic centers with a g factor of 2.0035, centers associated with the presence of protons in SiO₂ globules, and centers in the adsorbed film on the aerogel surface. The fast (T _fast = 30 h) and slow (T _slow = 70 d) processes have been revealed in the recombination of these centers.     

Nuclear spin-lattice relaxation in finely dispersed carbonizate powders

Finely dispersed carbonizate powders were studied with the aim of revealing their suitability for producing hyperpolarized noble gases. In the temperature and frequency dependences obtained over a wide range of temperatures and magnetic fields for the spin-lattice relaxation times of the magnetic moments of ³He, ¹H, and ¹³C nuclei, anomalous features caused by the suppression of the exchange between surface paramagnetic centers in a magnetic field were observed. It is shown that the interaction with magnetic moments of the ¹H nuclei situated near the paramagnetic centers is the main polarization-leakage channel for the noble-gas nuclear spins.     

Nuclear spin relaxation induced by a mechanical resonator

We report on measurements of the spin lifetime of nuclear spins strongly coupled to a micromechanical cantilever as used in magnetic resonance force microscopy. We find that the rotating-frame correlation time of the statistical nuclear polarization is set by the magnetomechanical noise originating from the thermal motion of the cantilever. Evidence is based on the effect of three parameters: (1) the magnetic field gradient (the coupling strength), (2) the Rabi frequency of the spins (the transition energy), and (3) the temperature of the low-frequency mechanical modes. Experimental results are compared to relaxation rates calculated from the spectral density of the magnetomechanical noise.     

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) with average crystallite sizes in the range of 20–50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO ₃ ^2? and which replace the positions of PO ₄ ^3? in the hydroxyapatite structure.     

Effect of quantum confinement and influence of extra charge on the electric field gradient in ZnO

By means of electron-nuclear double resonance (ENDOR), it is shown that the Al impurity, which acts as a shallow donor in ZnO, leads to a significant reduction of the electric field gradient in ZnO single crystals. In ZnO quantum dots, however, the gradient on the Al sites remains virtually unchanged. When the Zn²⁺ ion is substituted by Mn²⁺ in a ZnO single crystal, the electric field gradient slightly increases (by about 20%). Therefore, the Mn²⁺ ions can be used as probes to monitor the electric field gradients in ZnO crystals.     

Photostimulated conductivity in relaxors

Photoconductivity of lead magnesium niobate is studied, and the spectral dependence of the photo-conductivity is measured in the vicinity of the permittivity maximum associated with a diffuse phase transition. Photostimulated currents due to the Dember effect are detected. Based on the data obtained, the structure of the density of states of defect energy levels is discussed.     

EPR of Radiation-Induced Nitrogen Centers in Hydroxyapatite: New Approaches to the Study of Electron-Nuclear Interactions

Russian Journal of Coordination Chemistry - Radiation-induced impurity nitrogen centers ( $${\text{NO}}_{3}^{{2 - }}$$ ) in nanosized powders of synthetic hydroxyapatite are studied by pulse EPR...     

Generation of Optically Addressable Spin Centers in Hexagonal Boron Nitride by Proton Irradiation

Physics of the Solid State - The possibility of creating defects with spin-dependent fluorescence in a van der Waals material, namely, hexagonal boron nitride (hBN), by irradiating the latter with...     

Study of Organic Self-Assembled Nanosystems by Means of High-Frequency ESR/ENDOR: The Case of Oil Asphaltenes

An approach to investigate self-assembly of oil disperse systems based on high-field electron nuclear double resonance has been suggested. As exemplified by asphaltenes, the oil components most prone to self-assembly, the formation of planar rather than multilayer structures has been directly evidenced experimentally. The suggested method can be applied to elucidate the self-assembly mechanism in wide range of organic objects.