Electron paramagnetic resonance in YbNiAl<inf>2</inf> single crystals with strong magnetic anisotropy

© 2017, Pleiades Publishing, Ltd.Anisotropy in the magnetic properties of YbNiAl2 intermetallide has been studied. Electron paramagnetic resonance (EPR) signals assigned to the localized magnetic moments of trivalent ytterbium have been detected at temperatures below 20 K. Spin–lattice relaxation processes like the Orbach–Aminov process with participation of the first excited Stark sublevel of the Yb3+ ion with an energy of 96 K govern electron–spin dynamics and the disappearance of spectrum lines with a further increase in temperature. Strong magnetic anisotropy effects are discussed as a main reason for the appearance of electron paramagnetic resonance

Polytypism driven zero-field splitting of silicon vacancies in 6H -SiC

© 2018 American Physical Society. The fine-structure splitting in zero magnetic field allows one to access the coherent control and manipulation of polarized spin states. Here the zero-field splitting (ZFS) of the S=3/2 silicon vacancy-related centers in 6H-SiC is explored by means of electron paramagnetic resonance and electron nuclear double resonance techniques, combined with first-principle calculations. We show that the centers not only possess significantly different absolute values of ZFS, but they also differ in their sign. This diversity is rationalized by a flattened/elongated character of their spin-density distribution, potentially alters spin-photon entanglement, and suggests these centers for qubits in the upcoming technology of quantum communication and quantum-information processing

Radiation-induced stable radicals in calcium phosphates: Results of multifrequency epr, ednmr, eseem, and endor studies

This article presents the results of a study of radiation-induced defects in various synthetic calcium phosphate (CP) powder materials (hydroxyapatite—HA and octacalcium phosphate—OCP) by electron paramagnetic resonance (EPR) spectroscopy at the X, Q, and W-bands (9, 34, 95 GHz for the microwave frequencies, respectively). Currently, CP materials are widely used in orthopedics and dentistry owing to their high biocompatibility and physico-chemical similarity with human hard tissue. It is shown that in addition to the classical EPR techniques, other experimental approaches such as ELDOR-detected NMR (EDNMR), electron spin echo envelope modulation (ESEEM), and electronnuclear double resonance (ENDOR) can be used to analyze the electron–nuclear interactions of CP powders. We demonstrated that the value and angular dependence of the quadrupole interaction for14 N nuclei of a nitrate radical can be determined by the EDNMR method at room temperature. The ESEEM technique has allowed for a rapid analysis of the nuclear environment and estimation of the structural positions of radiation-induced centers in various crystal matrices. ENDOR spectra can provide information about the distribution of the nitrate radicals in the OCP structure. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Published under the CC BY 4.0 license.Authors would like to thank the Russian Foundation for Basic Research, project no. 18-29-11086. Institute of Solid State Physics, University of Latvia as the Center of Excellence received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01–2016-2017- TeamingPhase2 under grant agreement No. 739508, project CAMART2

Spin Centres in SiC for Quantum Technologies

© 2016, Springer-Verlag Wien.Atomic-scale colour centres in bulk and nanocrystalline SiC are promising for quantum information processing, photonics and sensing at ambient conditions. Their spin state can be initialized, manipulated and readout by means of optically detected magnetic resonance. It has been shown that there are at least two families of colour centres in SiC with S = 1 and S = 3/2, which have the property of optical alignment of the spin levels and allows a spin manipulation. The ground state and the excited state were demonstrated to have spin S = 3/2 and a population inversion in the ground state can be generated using optical pumping, leading to stimulated microwave emission even at room temperature. By controlling the neutron irradiation fluence, the colour centres concentration can be varied over several orders of magnitude down to a single defect level. Several, separately addressable spin centres have been identified in the same crystal for each polytype, which can be used either for magnetic field or temperature sensing. Some of these spin centres are characterised by nearly temperature independent zero-field splitting, making these centres very attractive for vector magnetometry. Contrarily, the zero-field splitting of the centres in the excited state exhibits a giant thermal shift, which can be used for thermometry applications. Finally coherent manipulation of spin states has been performed at room temperature and even at temperatures higher by hundreds of degrees. SiC is taking on a new role as a flexible and practical platform for harnessing the new quantum technologies

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20-50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO3 2- paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO3 2- radicals preferably occupy PO4 3- site in the HAp structure. © 2014 Pleiades Publishing, Inc

Properties of AlN single crystals doped with Beryllium via high temperature diffusion

© 2018 Author(s). We report on co-doping of high-quality AlN single crystals by group II Beryllium acceptors by means of diffusion from the vapour phase at a temperature of 1850 °C. We discovered that Be is characterized by the high diffusion length, allowing one to produce Be co-doping of sub-mm-thick AlN wafers. We show that Be diffusion led to the quenching of the visible (VIS) 450 nm (2.75 eV) and deep ultraviolet (UV) 265 nm (4.7 eV) optical absorption bands with simultaneous induction of the absorption band peaked at 248 nm (5 eV). By means of electron paramagnetic resonance (EPR), we also found that the presence of Be impurities compensated the donor type paramagnetic centers. Correlation of the EPR data with the optical absorption allowed us to conclude that Be produced in the AlN via diffusion acted predominantly as an acceptor, inducing the shift of the Fermi level to the lower part of the AlN bandgap. This shift of the Fermi level results in recharging of the deep level defects in the AlN bandgap, which explains the observed quenching of the VIS and UV absorption bands

Room Temperature High-Field Spin Dynamics of NV Defects in Sintered Diamonds

Sintered oriented nanodiamond arrays with the extremely high concentrations of the nitrogen-vacancy (NV) centers (up to 103 ppm) were investigated by the W-band (94 GHz) electron spin echo electron paramagnetic resonance techniques. The NV centers were fabricated by the high-pressure high-temperature sintering of detonation nanodiamonds (DND) without the post or prior irradiation of the samples. The processes of polarization and recovery of the equilibrium population of the spin sublevels by optical and microwave pulses have been examined at room temperature in high magnetic fields corresponding to the fine-structure transitions for the NV defects at 94 GHz (3,250-3,450 mT). A long spin coherence time of 1.6 μs and spin-lattice relaxation time of 1.7 ms were measured. The results were compared with those obtained on the NV centers fabricated by the irradiation and subsequent annealing of the commercially available bulk diamonds. It was shown that the relaxation characteristics of the NV defects were similar in the both types of the samples despite the extremely high concentrations of NV defects and isolated nitrogen donors in the sintered DND. © 2013 Springer-Verlag Wien