Experimental evidences of the shape-induced structural distortion of SrTiO3 single crystals from impurity Mn4+ ions electron paramagnetic resonance

A study of high-quality SrTiO3 single crystals doped with the Mn4+ ions in the cubic phase (T > 105 K) with X-band electron paramagnetic resonance reveals direct correspondence between a shape of a sample and magnetic anisotropy of the impurity Mn4+ centers. In particular, for a sample with the shape of a square base rectangular prism, a size of (a × a × h) and faces perpendicular to the crystallographic directions, zero-field splitting parameter D is approximately proportional to (a / h − 1) quantity. Temperature dependence of D indicates that this peculiar symmetry lowering is a feature characteristic for the cubic Fm3m phase of the strontium titanate. Diminishing of the D value with the decrease of the surface roughness for a thin (001)-oriented SrTiO3:Mn platelet shows that the observed effect originates from the sample surface

ENDOR study of nitrogen hyperfine and quadrupole tensors in vanadyl porphyrins of heavy crude oil

We report the observation of pulsed electron-nuclear double resonance (ENDOR) spectrum caused by interactions of the nitrogen nuclei 14N with the unpaired electron of the paramagnetic vanadyl complexes VO2+ of vanadyl porphyrins in natural crude oil. We provide detailed experimental and theoretical characterization of the nitrogen hyperfine and quadrupole tensors

Creation of negatively charged boron vacancies in hexagonal boron nitride crystal by electron irradiation and mechanism of inhomogeneous broadening of boron vacancy-related spin resonance lines

Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (V−B ). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating V−B centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the V−B centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the V−B spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the V−B spin embedded in the hBN as a probe

Symmetry breaking in single-crystal SrTiO<inf>3</inf>plates: EPR manifestations

Results of the electron paramagnetic resonance (EPR) studies of Fe3+ and Mn4+ impurity centers in high-quality single-crystal SrTiO3 plates with thickness h < 1 mm are presented. Impurities served the paramagnetic probes of the crystal structure. Analysis of the collected data indicates that the symmetry of the crystal structure of thin (001) and (110) oriented strontium titanate plates above 105 K lowers in the bulk from the cubic to tetragonal. The structure of this high-temperature tetragonal state is different from that of the conventional low-temperature antiferrodistorsive phase and has not been reported for SrTiO3 before. It is shown that the effect does not originate from the residual stress; its magnitude and particular manifestations depend on plate orientation, surface quality and geometry of a sample. Peculiarities of the observed phenomenon are presented and the possible scenario of its realization is discussed