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In the high-frequency ENDOR experiments, the hyperfine (HF) interaction between the unpaired electron of the shallow donor or shallow acceptor and the nuclear spins of the Coulombic center and the surrounding atoms is determined, which is then translated into the spin density of the electronic wave function at the various atomic positions. The results of studying the spatial distribution of wave functions for shallow donors in ZnO, AgCl, AlN, and SiC crystals, ZnO-based nanostructures, and shallow boron acceptors in SiC will be presented. The change of the electronic wave function of a shallow donor in ZnO quantum dots (QDs) when entering the regime of quantum confinement by using the nuclear as probes has been observed. The model, based on the effective mass approximation (EMA), that describes a 1s-like wave function with the Bohr radius of ~ 1.5 nm for distant shells was tested. The EMA does not yield an appropriate description of the electronic wave function when the radius of the QD is reduced below the Bohr radius. The direct reconstruction of the wave function of the intrinsic shallow electronic center (SEC) and self-trapped excitons in AgCl was presented. The SEC was suggested to be an electron that is shallowly trapped by two adjacent silver ions on a single cationic site (split-interstitial position), so-called “latent image” in silver halides. The shallowly trapped electron of the STE is shown to behave like a hydrogen 1s electron, centered on the Ag+ lattice position, with a Bohr radius r0 = 1.51 nm that is in agreement with Bohr radius of SEC (r0 = 1.66 nm). For SEC in AgBr, r0 = 2.48 nm. It was demonstrated that dynamic nuclear polarization of nuclear spins due to hyperfine interactions with ligand nuclei can be achieved in ZnO (and based QDs) and AgCl by saturating the high-frequency EPR transition of a shallow donor at low temperatures corresponding to a high Boltzmann factor. Several types of shallow donors were indicated in AlN crystals: (i) affected by the DX-relaxation and (ii) with normal behavior. The strong HF interaction for light-induced SD in AlN support the assignment to the impurity in anionic sublattice (e.g. oxygen in N position). At the same time, a shallow donor with normal behavior can belong to Si or C in the Al position. The electronic structure of shallow donors and shallow acceptors in silicon carbide was investigated by the ENDOR method. The spin density of the N donor corresponding to the observed ENDOR lines was established to be p like in character and located mainly on the Si atoms for the k site in 4H-SiC, whereas for the three sites in 6H-SiC the spin density is s-like in character and located mainly on the C atoms. An explanation for the difference in the electronic wave function of the N donor in 4H-SiC and 6H-SiC can be found in the large difference in the band structure of the two polytypes and in the position of the minima in the Brillouin Zone. The electronic density for shallow B acceptor substituting Si in the k position is distributed in an ellipsoidal shape with the main symmetry axis making an angle of 70° with the c axis, i.e., along the direction of the B–C with main spin density.

The effects of the high-temperature (T = 1880°C) diffusion of beryllium ions and of electron irradiation on the optical properties of single-crystal aluminum nitride is studied. It is shown that the introduction of Be into AlN results in a change in the spectral characteristics of Raman scattering and infrared absorption. The analysis of Raman spectra and infrared adsorption spectra in crystals containing the Be impurity proves that this impurity is a getter of intrinsic defects responsible for the yellow color of the AlN crystal and for the broadening of lines in the spectra.

A family of atomic-scale color centers, the spin state of which can be controlled via optical and microwave channels, has been found in the rhombic polytype of silicon carbide 21R-SiC considered as a natural superlattice. Zero-phonon lines are observed in photoluminescence corresponding to spin-3/2 centers, which differ in fine structure splitting in the ground and excited states. Giant changes in the photoluminescence intensity under conditions of magnetic resonance and anticrossing of the spin levels of the ground and excited states are demonstrated, which open up possibilities for applications in magnetometry, thermometry, and quantum computing.

In yttrium aluminum garnet (YAG) crystals containing terbium and cerium impurities, along with the main EPR signals of Tb3+ and Се3+ ions located in the dodecahedral sites of the YAG lattice in a regular environment, EPR lines with a lower (several percent) intensity were observed. They also belong to the paramagnetic centers of terbium and cerium, but are characterized by slightly altered parameters—the initial level splitting for non-Kramers Tb3+ ions and g-factors for Се3+ ions. It is shown that the nature of such centers and their number can be explained by the presence of YAl antisite defects, i.e. yttrium ions in the octahedral aluminum positions, in the environment of Tb3+ and Се3+.

The methods of high-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE) and optically detected magnetic resonance (ODMR) are used to study the unique properties of nitrogen-vacancy (NV) defects in diamond in strong magnetic fields. It is shown that in strong magnetic fields (∼3–5 T) there occurs an effective optically induced alignment of populations of spin levels resulting in filling the level MS = 0 and emptying of the levels MS = ±1, that makes it possible to record ODMR using the change in the intensity of photoluminescence which reaches 10% at resonance. It is demonstrated that the efficiency of the alignment has the same order as in zero and low magnetic fields. The samples were preliminary studied by the ODMR method in zero magnetic fields that allowed accurate determination of the main parameters of the fine structure and hyperfine interactions with nitrogen nuclei, as well as dipole-dipole interactions between the NV center and deep nitrogen donors in the form of a nitrogen atom replacing carbon, N0. Hyperfine interactions with the nearest carbon atoms (isotope 13C) were observed in the high-frequency ODMR spectra, that opens up opportunities for measuring the processes of dynamic polarization of carbon nuclei in strong magnetic fields using optical methods. It is assumed that narrow ODMR lines in strong magnetic fields can be used to measure these fields with submicron spatial resolution. A new method for recording ODMR of NV centers with microwave frequency modulation has been developed, which simplifies the technique of measuring high magnetic fields. A significant increase in the intensity of the ODMR signal was demonstrated when a strong magnetic field was oriented along the symmetry axis of the NV center.

A magnetic resonance spectrometer operating at several fixed frequencies in the millimeter range is designed on the basis of a new generation of microwave bridges and a cryogen-free magneto-optical cryogenic system. The spectrometer allows measurements of EPR in continuous wave and pulse (free-induction decay, FID and electron spin echo, ESE) modes, photo-EPR, and optically detected magnetic resonance (ODMR) in a wide range of temperatures (1.5–300 K) and magnetic fields (up to 7 T with the ability to invert the field). It is based on a line of unified microwave bridges with a powerful oscillator and a superheterodyne receiver. Currently, they operate in W and D bands (at 94 and 130 GHz, respectively), but the frequency bands can be extended. In addition to highly stable fixed-frequency oscillators with narrow spectrum (better than − 100 dBc at 10 kHz offset at 94 GHz), they have variable frequency oscillators, which simplify tuning of the microwave circuit with a resonator and allow operation with frequency modulation when using a non-resonant microwave system. In the latter, it is possible to study large samples and quickly change the operating frequency of the spectrometer, simply replacing the microwave bridge. For all frequencies, the spectrometer uses common hardware and original software. The performance of the spectrometer at 94 GHz and 130 GHz was tested in measurements of CW-EPR, ESE and ODMR of NV defects in diamond single crystals, Tb3+ and Ce3+ ions in yttrium aluminum garnet crystals, nitrogen donors, and V3+ ions in 6H-SiC.

Optically detected magnetic resonance with temperature sweep is developed using the temperature dependence of the spin Hamiltonian parameters of paramagnetic color centers in silicon carbide. The detection is based on natural optical alignment of spin level populations over a wide temperature range including room temperature and on the change of these populations during level anti-crossing or cross-relaxation processes.

The advantage of the high-frequency spectroscopy of electron paramagnetic resonance (EPR) for the identification of nitrogen donors and a deep compensating vanadium impurity in various crystallographic positions of the silicon-carbide crystal is shown. Measurements are performed using a new generation EPR spectrometer operating in the continuous wave and pulsed modes at frequencies of 94 and 130 GHz in a wide range of magnetic fields (–7–7 T) and temperatures (1.5–300 K). A magneto-optical closed-cycle cryogenic system (Spectormag PT), highly stable generators (94 and 130 GHz), and a cavity-free system for supplying microwave power to the sample are used.

High-frequency pulsed electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) were used to determine electron nuclear interactions on remote ligand shells of silicon and carbon in spin-3/2 color centers with an optically induced high-temperature spin alignment in hexagonal $4H$-, $6H$-, and rhombic $15R$-silicon carbide (SiC) polytypes. The EPR and ENDOR experimental data relate unambiguously to spin-3/2 centers in which the optically induced alignment of the spin-level populations occurs. The identification is based on resolved ligand hyperfine interactions with carbon and silicon nearest, next-nearest, and the more distant neighbors and on the determination of the unpaired electron spin densities. The hyperfine interactions with $^{29}\mathrm{Si}$ and $^{13}\mathrm{C}$ nuclei are unambiguously separated due to the selective population of the fine-structure levels with certain values of ${\mathrm{M}}_{\mathrm{S}}$. The signs of these interactions and, as a result, the signs of oscillating spin density at $^{29}\mathrm{Si}$ and $^{13}\mathrm{C}$ nuclei, are determined. On the basis of the EPR and optically induced ENDOR measurements, signs of the fine-structure splitting for all the centers were demonstrated, which made it possible to establish the character of optically induced spin alignment, including the inverse populations of the spin levels for these centers. The values of hyperfine interaction with $^{29}\mathrm{Si}$ and $^{13}\mathrm{C}$ nuclei, including those remote from the localization of the spin-3/2 center, are tabulated, which can be used by a number of algorithms in quantum information processing as long-term memory.

Nitrogen-vacancy NV– centers, which are of considerable interest for quantum electronics, are artificially produced in the diamond structure by irradiation and subsequent annealing. In this work, these centers were revealed in natural diamonds of cubic habit (type IaA + Ib according to physical classification) from an industrial placer deposit of the Anabar River (NE Siberian platform) using the method of optically detected magnetic resonance (ODMR). Localization of the NV– centers in the dislocations slip planes {111}, separated by distances of about 5 μm, was established by means of scanning the ODMR and PL signals with a submicron resolution. In various crystals, one or two intersecting systems of such slip planes have been revealed. The largest amounts of these defects were found in the peripheral zones of crystals containing increased amounts of single isomorphic nitrogen atoms in the structure. The data obtained indicate the formation of the NV– centers in natural diamonds under post-crystallization plastic deformation, i.e., by a mechanism that differs from the widely used method of their artificial production.

Electron paramagnetic resonance (EPR) spectra of Ce3+, Yb3+, Cr3+, and Gd3+ impurity ions in yttrium aluminum garnet Y3Al5O12 (YAG) ceramics were detected and identified at frequency of 94 GHz. The advantage of measuring the EPR spectra in the high-frequency range compared to the standard EPR technique is shown, which makes it possible to separate the EPR spectra characterized by different anisotropic g-factors and also to isolate the EPR signals due to the splitting of the fine structure for centers with high-spin states. In ceramics with a high content of magnetic Gd3+ ions, EPR and electron spin echo (ESE) spectra of multi-ionic gadolinium complexes were observed, and EPR spectra of complexes with the maximum number of exchange-coupled gadolinium ions are seen at low temperatures. The temperature dependences of the EPR spectra indicates ferromagnetic ordering of exchange-coupled complexes of gadolinium.

Mn2+ ions in yttrium positions have been studied by means of optically detected magnetic resonance (ODMR) via Mn2+ spin-dependent emission in manganese-doped yttrium aluminum garnet crystals. It was shown that the intensity of photoluminescence excited by circularly polarized light depends on the population of the spin sublevels of the Mn2+ ground state and therefore can be used to study the ODMR. EPR measurements have confirmed that Mn2+ ions in the crystals under study occupy preferentially dodecahedral positions in the YAG lattice. Observation of forbidden transitions in the ODMR spectra has proved that the observed ODMR signals belong to Mn2+. Thus the wavelength dependence of the ODMR amplitude reveals the emission band of Mn2+ ions at dodecahedral positions in YAG:Mn.

Demands for miniaturization, increasing the operation speed and energy efficiency of electronic devices led to the emergence and rapid development of spin electronics, or spintronics. Several areas of experimental and theoretical research are considered, in which the Ioffe Institute is actively involved. We discuss current progress in developing semiconductor and hybrid structures that exhibit specified magnetic properties, the development of methods for manipulating individual spins, a theoretical description of switching of metallic heterostructures magnetization by an electric field, and ultrafast control of magnetization via manipulating the magnetic anisotropy by femtosecond laser pulses.

We review the history and modern state of silicon carbide and SiC-based devices. The main techniques for growing bulk SiC crystals and epitaxial SiC films are discussed. Epitaxial SiC structures used for post-growth processing are briefly reviewed. The state of the art achieved in developing SiC devices is presented. The main problems that occur in developing SiC equipment and prospects for designing and developing such equipment are analyzed.

A scanning optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of hole burning in the signal of optically detected magnetic resonance (ODMR) on atomic-sized color centers in silicon carbide crystals under conditions of spin level saturation by means of additional high-frequency resonance pumping. An increase in the sensitivity is achieved due to narrowing of the ODMR line and increasing slope of the dependence of signal frequency on the magnetic field.

Coherent spin manipulations of spin-$\frac{3}{2}$ color center ensembles in 6H-SiC crystal have been studied in high magnetic fields using methods of pulsed electron paramagnetic resonance, Rabi oscillations, and pulsed electron-electron double resonance under optical alignment conditions of the spin level populations. Rabi oscillation experiments show room temperature coherent control of these spin-$\frac{3}{2}$ color center ensembles in strong magnetic fields. A sharp decrease of the spin-lattice relaxation time ${T}_{1}$, \ensuremath{\sim}40 times, was observed in 6H-SiC at magnetic field of \ensuremath{\sim}3.5 T with increasing temperature from 100 to 300 K, while the spin-spin relaxation time ${T}_{2}$ is only shortened by \ensuremath{\sim}1.3 times. With an increase in the magnetic field, the times ${T}_{1}$ and ${T}_{2}$ were shown to decrease. The relaxation time ${T}_{1}$ in the case of magnetic field directed along the axis of the spin-$\frac{3}{2}$ center is \ensuremath{\sim}2 times longer than ${T}_{1}$ in magnetic field perpendicular to this axis. Relaxation times of the spin center in crystal grown with a reduced concentration of an isotope $^{29}\mathrm{Si}$ are significantly longer than crystal, with the natural content of isotopes. With a decrease in the $^{29}\mathrm{Si}$ content in our experiments by a factor of \ensuremath{\sim}5, the effective nuclear spin bath in SiC is reduced by a factor of \ensuremath{\sim}2. In a zero magnetic field resonance, transitions are allowed as magnetic dipole transitions with frequency ${\ensuremath{\omega}}_{0}$ which correspond to the zero-field splitting. In zero magnetic field and in fixed magnetic fields, the Rabi frequency was shown, using so-called ``Feynman-Vernon-Hellwarth transformation,'' to be ${\ensuremath{\omega}}_{R}=|\ensuremath{\gamma}|{B}_{1}$. In pulsed electron-electron double resonance experiments, a change in the intensity of the electron spin echo signal corresponding to one of the spin-allowed fine structure transitions is recorded depending on the sweep of the second frequency. The experiments show the possibility to coherently detect the optical spin alignment between ${M}_{S}=\ifmmode\pm\else\textpm\fi{}\frac{3}{2}$ via optically pumped silent ${M}_{S}=\ifmmode\pm\else\textpm\fi{}\frac{1}{2}$ sublevels of the spin-$\frac{3}{2}$ color centers, including a detection of Rabi oscillations.

Silicon vacancies in silicon carbide have been proposed as an alternative to nitrogen vacancy centers in diamonds for spintronics and quantum technologies. An important precondition for these applications is the initialization of the qubits into a specific quantum state. In this work, we study the optical alignment of the spin 3/2 negatively charged silicon vacancy in $6H\text{\ensuremath{-}}\mathrm{SiC}$. Using time-resolved optically detected magnetic resonance, we coherently control the silicon vacancy spin ensemble and measure Rabi frequencies, spin-spin and spin-lattice relaxation times of all three transitions. Then to study the optical initialization process of the silicon vacancy spin ensemble, the vacancy spin ensemble is prepared in different ground states and optically excited. We describe a simple rate equation model that can explain the observed behavior and determine the relevant rate constants.

Silicon carbide (SiC) hosts many interesting defects that can potentially serve as qubits for a range of advanced quantum technologies. Some of them have very interesting properties, making them potentially useful, e.g., as interfaces between stationary and flying qubits. Here we present a detailed overview of the relevant properties of the spins in silicon vacancies of the $6H$-SiC polytype. This includes the temperature-dependent photoluminescence, optically detected magnetic resonance, and the relaxation times of the longitudinal and transverse components of the spins during free precession as well as under the influence of different refocusing schemes.

Optical and radio-frequency physical effects that allow spin manipulations at room temperature using magnetic resonance, effects of anticrossing levels in the ground and excited quadruplet spin states, and cross-relaxation resonances in ensembles of spin color centers in silicon carbide micro- and nanocrystals have been demonstrated. A scanning device where ensembles of spin centers placed on the tip of the cantilever probe of an atomic force microscope serve as sensors of magnetic and temperature fields with a submicron spatial resolution has been considered.

A new diagnostic method for evaluation of the local polytypic composition of silicon carbide at room temperature is proposed using known and tabulated zero-field splitting values for spin color centers with S = 3/2 whose frequency parameters are in the megahertz range and depend on the specific polytype. The zero-field splitting values are recorded from the change in the photoluminescence in the near infrared, either under the optically detected magnetic resonance conditions or under the level anticrossing conditions of the spin centers. The proposed method can be used to identify silicon carbide known as carborundum in nature by recording optically induced radio frequency emission of spin color centers, including outer space.

An optical quantum thermometer with a submicron spatial resolution that is based on the physical phenomenon of optical response in the system of spin centers in silicon carbide under conditions of cross-relaxation between the optically active centers in quadruplet spin state and triplet centers, where there is anomalously strong dependence of the splitting of the fine structure on temperature, has been proposed.

Results of investigations of Group III acceptors (B, Al, and Ga) in crystals of silicon carbide using the most informative electron spin resonance and electron nuclear double resonance methods are presented. Structural models of the acceptors with shallow and deep levels are considered. In addition to the data obtained earlier, studies using high-frequency magnetic resonance were obtained, which allowed revealing orthorhombic deviations from the axial symmetry for the deep acceptors; theoretical analysis explains experimentally found shifts of g factors for the deep acceptors arising due to the orthorhombic deviations, which appear probably due to the Jahn–Teller effect.

The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4H-SiC and 6H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.

The electronic structure of non-Kramers ${\mathrm{Tb}}^{3+}$ centers in single crystals of yttrium aluminum garnet (YAG) was studied using a new-generation high-frequency magnetic resonance spectrometer that allows measurements of electron paramagnetic resonance (EPR), electron spin echo (ESE), the photon echo on hyperfine components of Stark levels in zero magnetic field, and optically detected magnetic resonance (ODMR). It was created on the basis of a highly stable microwave bridge operating in the near-terahertz region (0.094 or 0.130 THz), both in continuous-wave (cw) and pulse modes, a nonresonant system for supplying microwave power to a sample, and a cryogen-free magneto-optical cryostat. EPR, ESE, and cw measurements at two frequencies allowed us to reliably and with high accuracy determine the parameters of ${\mathrm{Tb}}^{3+}$ centers that occupy yttrium dodecahedral positions in YAG: ${g}_{||}=15.8\ifmmode\pm\else\textpm\fi{}0.2$, ${g}_{\ensuremath{\perp}}\ensuremath{\approx}0$ (|| corresponds to one of the $\ensuremath{\langle}100\ensuremath{\rangle}$ crystal axes), the zero-field splitting $\mathrm{\ensuremath{\Delta}}=2.705\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$, and the hyperfine interaction constant $A=0.197\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. In addition to the ${\mathrm{Tb}}^{3+}$ centers in a regular environment, EPR spectra with lower intensity and a resolved hyperfine structure were found for at least three types of additional ${\mathrm{Tb}}^{3+}$ centers. They have symmetry, $g$ factors, and hyperfine interaction constants which are close to those of the main ${\mathrm{Tb}}^{3+}$ centers but differ in the zero-field splitting parameters \ensuremath{\Delta} that strongly depend on the crystal field. They were ascribed to ${\mathrm{Tb}}^{3+}$ centers with nearby antisite ${\mathrm{Y}}_{\mathrm{Al}}$ defects. Similarity with several types of ${\mathrm{Ce}}^{3+}$ centers in YAG crystals, the types, and relative concentrations of antisite defects are discussed. For one of the additional ${\mathrm{Tb}}^{3+}$ centers, splitting of the energy levels in the zero field turned out to be close to an energy of 94 GHz microwave quanta, and intense echo signals were observed in weak magnetic fields and in the zero field corresponding to the EPR transitions between the hyperfine components of the ${\mathrm{Tb}}^{3+}$ spin levels. ODMR spectra of ${\mathrm{Tb}}^{3+}$ centers in YAG crystals, containing Ce and Tb, were obtained by monitoring the intensity of the ${\mathrm{Ce}}^{3+}$ luminescence, which implies the transfer of energy from ${\mathrm{Tb}}^{3+}$ ions to ${\mathrm{Ce}}^{3+}$ ions with conservation of spin. This result seems to be important, since these systems are of interest for quantum communication and computations. Taking into account that cerium does not have isotopes with a nuclear spin and that terbium has 100% $^{159}\mathrm{Tb}$ having nuclear spin $I=3/2$ and a sufficiently large nuclear magnetic moment, the ${\mathrm{Tb}}^{3+}\ensuremath{-}{\mathrm{Ce}}^{3+}$ system in garnet crystals can be promising for coherent information processing. ${\mathrm{Tb}}^{3+}$ ions can play a role of qubits and ${\mathrm{Ce}}^{3+}$ ion with a lifetime of about 50 ns, and almost unity quantum efficiency of optical transitions can be used as a single-ion readout arrangement. The prospects for using this system as hardware for quantum communication and computations are discussed.

Inversion recovery with electron spin-echo detection has been used to study the electron spin-lattice relaxation rates 1 / T 1 for transition metal impurities in heavily cobalt-doped hydrothermally grown ZnO single crystals. The relaxation dynamics of Co 2 + ions dominates the phonon bottleneck effect in the Orbach-Aminov process, which involves the modulation of the zero-field-splitting tensor. The relaxation mechanism may be treated in terms of phonon heating with fast rate of energy pump from Co 2 + spins into the lattice phonon modes. The measurements reveal the cross-relaxation process in which the single Co 2 + ions cross-relax to exchange-coupled clusters of cobalt ions. The higher temperature relaxation of Co 2 + indicates an additional Orbach-Aminov process via a state of ∼ 226 cm − 1 above the ground state Kramers doublet. It is shown that in this system Co 2 + ions play a role of the rapidly relaxing centers, strongly mediating the spin-lattice relaxation of the other transition metal impurities, such as Mn 2 + and Fe 3 +.Inversion recovery with electron spin-echo detection has been used to study the electron spin-lattice relaxation rates 1 / T 1 for transition metal impurities in heavily cobalt-doped hydrothermally grown ZnO single crystals. The relaxation dynamics of Co 2 + ions dominates the phonon bottleneck effect in the Orbach-Aminov process, which involves the modulation of the zero-field-splitting tensor. The relaxation mechanism may be treated in terms of phonon heating with fast rate of energy pump from Co 2 + spins into the lattice phonon modes. The measurements reveal the cross-relaxation process in which the single Co 2 + ions cross-relax to exchange-coupled clusters of cobalt ions. The higher temperature relaxation of Co 2 + indicates an additional Orbach-Aminov process via a state of ∼ 226 cm − 1 above the ground state Kramers doublet. It is shown that in this system Co 2 + ions play a role of the rapidly relaxing centers, strongly mediating the spin-lattice relaxation of the oth...

Level anticrossing (LAC) spectroscopy has been demonstrated on a family of uniaxially oriented spin color centers with S = 3/2 in the ground and excited states in hexagonal 4H-, 6H-, and rhombic 15R-SiC polytypes. It has been shown that these centers exhibit unique characteristics such as optical spin alignment up to the temperatures of 250°C. A sharp variation of the IR photoluminescence intensity in the vicinity of LAC with the record contrast has been observed, which can be used for a purely all-optical sensing of the magnetic field and temperature without applying radiofrequency field. A distinctive feature of the LAC signal is weak dependence on the direction of the magnetic field that allows one to monitor the LAC signals in the nonoriented systems, such as powder of SiC nanocrystals.

The unique quantum properties of nitrogen-vacancy color centers (NV centers) in diamond have motivated the search for similar color centers with enhanced properties in SiC. In this paper, experimental evidence is presented that vacancy-related spin centers in SiC not only have properties similar to those of diamond NV centers but also exhibit many additional properties, making these quantum systems promising for various applications in spintronics, sensorics, and quantum information processing under ambient conditions.

Electron paramagnetic resonance (EPR) in the ground state of Gd3+ ions in (LuGd)3 Al5O12 single crystals has been found by monitoring the Ce3+ photoluminescence intensity under circularly polarized excitation in the presence of the 35 GHz microwave field. Due to spin selection rules for optical transitions, the circularly polarized excitation allowed monitoring the populations of the Ce3+ ground-state spin sublevels, which can be changed at the EPR of Gd3+ due to Gd–Ce cross relaxation.

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.

An optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of optical response in a solid-state spin system under conditions of spin sublevel anticrossing without using a resonance frequency. The system operation is demonstrated by example of spin defects in silicon carbide of various polytypes.

An optical quantum thermometer with submicrometer resolution is proposed. Its operation is based on the physical phenomenon of the optical response in a system of spin centers in silicon carbide under conditions of anticrossing of spin sublevels of the excited quadruplet state (S = 3/2) with temperature-dependent fine-structure splitting.

We describe a series of high-frequency EPR/optically detected magnetic-resonance (ODMR) spectrometers operating in both continuous-wave and pulsed regimes in 2-, 3-, 4-, and 8-mm. The resonance signal can be monitored in both microwave and optical detection channels. The entire series of EPR/ODMR spectrometers has common design features.

Atomic-scale colour centres in bulk and nanocrystalline SiC are promising systems for quantum photonics compatible with fiber optics, quantum information processing and sensing at ambient conditions. Colour centres which acts as stable single photon sources in SiC can be key elements for quantum photonics and communications. 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 even at room temperature and above. The spin state can be initialized, manipulated and readout by means of optically detected magnetic resonance (ODMR), level anticrossing and cross-relaxation. Recently, we observed the effects of “hole burning” in the ODMR spectra, which made it possible to narrow the ODMR line by approximately an order of magnitude, which substantially increases the possibilities of technological applications of spin centres.

Exchange-coupled complexes consisting of Mn ions and holes have been revealed by optically detected magnetic resonance in the narrowest quantum wells of asymmetrical multiple-quantum-well structures (CdMn)Te/(CdMg)Te. Calculations have been performed to estimate the parameters of the complexes (exchange interactions and hole g-factors) and simulate the spectra. The formation of such complexes implies the directional electron tunneling from narrow to larger wells, i.e., an electron cascade, which results in the creation of the excess hole concentration in the narrowest and intermediate-width quantum wells.

A method for determining the orientation of nitrogen-vacancy (NV) defect structure orientation in diamond crystals and nanodiamonds is proposed, which is based on the optically detected magnetic resonance technique with magnetic field modulation and microwave frequency scanning.

Atomic-scale defects in silicon carbide exhibit very attractive quantum properties that can be exploited to provide outstanding performance in various sensing applications. Here we provide the results of our studies of the spin-optical properties of the vacancy related defects in SiC. Our studies show that several spin-3/2 defects in silicon carbide crystal are characterized by nearly temperature independent axial crystal fields, which makes these defects very attractive for vector magnetometry. The zero-field splitting of another defect exhibits on contrast a giant thermal shift of 1.1 MHz/K at room temperature, and can be used for temperature sensing applications.

Long-lasting afterglow of ZnO single crystals grown by hydrothermal method has been studied using high-frequency (94 GHz) optically detected magnetic resonance (ODMR) at helium temperatures. Giant (up to 30%) afterglow intensity-detected electron paramagnetic resonance signals of shallow donors and deep acceptors, which are lithium atoms substituting for zinc in the ZnO lattice, unambiguously indicate a spin-dependent character of the donor-acceptor recombination. The observed variations in the shape of the afterglow-detected ODMR spectra of lithium acceptors with time passed after irradiation are associated with the difference in the recombination rates of shallow donors with axial and non-axial LiZn centers and with a change in the recombination character with time.

Nowadays semiconductor and solid-state physics appears to be the physics of systems with reduced dimensionality. Fabrication of single or periodic potential wells by simply combining two materials with different energy gaps and spatial dimensions confining the motion of electrons and holes results in exciting new effects that originate in the size dependence of quantum phenomena.

We present a brief historical introduction to the field of pulse magnetic resonance (see, e.g., [1]). The first EPR phenomenon was observed by Zavoisky in 1944 [2]. In 1946 Bloch [3] and Purcell et al. [4] reported the first nuclear magnetic resonance (NMR) experiments.