Applied Magnetic Resonance最新文献

Electron and nuclear spins in solids, coherently coupled to photons, provide promising resources for quantum information processing and sensing. Obtaining information about short-lived excited states is critical for realizing ultrafast all-optical spin control methods. After a brief review of early magnetic resonance studies of excited states, the following representative examples of the use of magnetic resonance spectroscopy to study excited states in wide-gap materials, semiconductors and nanostructures based on them will be considered: (1) optically detected magnetic resonance (ODMR), electron spin echo, electron-nuclear double resonance in the excited state on the example of self-trapped excitons in ionic-covalent silver halide crystals and nanocrystals, (2) ODMR and level anticrossing (LAC) spectroscopy of localized heavy-hole excitons in semiconductor quantum wells and superlattices, (3) LAC and ODMR in excited states of spin centers in diamond and silicon carbide, (4) the use of LAC and cross-relaxation for all-optical sensing with submicron spatial resolution.

The Europium rare-earth manganites, La_0.7−xEu_xSr_0.3MnO₃ (x = 0.0–0.7), were investigated by the technique of X-band electron paramagnetic resonance (EPR) in the temperature range from 30 to 500 K. As the temperature was lowered, the various samples made transitions from paramagnetic to ferromagnetic phases. Furthermore, coexistence of anywhere from two to three ferromagnetic phases in the various samples was found. The third ferromagnetic phase was observed only in the samples with x = 0.1, 0.2, 0.3. The Curie temperatures for the various samples were estimated from the characteristics of the variable-temperature EPR spectra. The EPR data indicated the presence of Griffiths phases in the samples with x = 0.2, 0.3, 0.4, 0.5, 0.6, from which the respective Griffiths temperatures were determined. The activation energies were estimated here from the EPR data using the hopping model. The EPR linewidth behavior is found to be consistent with that predicted by the bottlenecked spin-relaxation model. The perovskite La_0.5Eu_0.2Sr_0.3MnO₃ is potentially useful in the design of magnetocaloric refrigeration units as a working fluid, since its Curie temperature T_C is found to be close to the room temperature. The various ferromagnetic components in the samples observed here have been resolved only by the technique of EPR, not possible by other techniques.

The spectrum of continuous-wave electron paramagnetic resonance (CW-EPR) was analyzed with respect to the shape of the line under microwave (MW) power saturation (({P}_{MW}sim {B}_{1}^{1/2};{B}_{1}) is intensity of MW magnetic field). The used ({B}_{1}) increases until the Rabi frequency (({omega }_{1}=gamma {B}_{1}), (gamma) is the electron gyromagnetic ratio) approaches the radiofrequency (left({omega }_{rf}right)) used as the magnetic modulation frequency. The possible effect of Rabi resonance (left({omega }_{1}={omega }_{rf}right)), on spin packets system can be detected under the condition of “weak modulation near the Rabi resonance” (({omega }_{2}ll {omega }_{1}approx {omega }_{rf})) where ({omega }_{2}) is modulation amplitude of radiofrequency field expressed in frequency units. Inhomogeneously broadened, CW-EPR, lines of the P1 (N_s⁰) nitrogen centers (30 ppm > [N_s⁰] < 200 ppm) in diamond crystal and E’ defect in irradiated vitreous SiO₂ with long spin relaxation times (({T}_{1}) and ({T}_{2}) ranged in the interval from around 2 ms to 1 µs at room temperatures) were selected for saturation study. Spectra were recorded using magnetic field modulation (({omega }_{rf}/2pi =100) kHz) with modulation amplitude (({omega }_{2}/2pi =27text{ kHz})) as the first harmonic for two phase-sensitive detections, detection in-phase with respect to the modulation frequency and detection 90° out-of-phase with respect of the modulation frequency. For the later detection, the resulting change near Rabi resonance can be related to the expected inversion of modulation sideband lines under resonance conditions. This effect detected in the saturation process on inhomogeneous spectral lines of P1 and E’ centers shows that both samples can be used as a standard for estimation ({B}_{1}) value.

It is acknowledged that a solid-state foundation for qubit implementation can be found in optically active high-spin vacancy-type defects (color centers) in semiconductors. Silicon carbide (SiC) crystals serve as a reliable host for defects, positioning them as strong competitors to the well-known nitrogen vacancy ({NV}^{-}) centers in diamond. This paper reports on photoinduced electron paramagnetic resonance (W-band, 94 GHz) spectroscopy measurements on 4H and 6H polytype SiC crystals which exhibit distinct optically polarizable color centers due to their unique structural and electronic properties. Spin defects such as negatively charged nitrogen vacancy centers and divacancies excited at 532 nm, are present in 4H-SiC. By contrast, only ({NV}^{-}) centers excited at 980 nm are found in 6H-SiC across a wide temperature range. These features make the 6H-SiC color centers promising for quantum technologies because of their excitation and luminescence in the near-infrared telecommunications range, as well as their ability to selectively target the resonant excitation of individual-based qubits.

The local ordering and features of the molecular mobility of water confined in voids of a pure silica mordenite were studied using the molecular dynamics simulation over a temperature range from 298 to 163 K. The simulated system was a fragment of mordenite consisted of 2 × 2 × 4 unit cells filled with 384 water molecules. Three different water models: SPCE, SPCF, and TIP5P were considered. To study the effect of nanoconfinment, the results were compared with bulk water. The modeling suggests that at room temperature, a 2D (in c and b directions of the mordenite cell) water diffusion takes place, while upon cooling, the diffusion in b direction essentially slows down. The analysis of microstructure shows that the pores prevent the formation of a full tetrahedral structure of water environment that results in formation of several water substructures. A detailed analysis of water reorientational motion was carried out and the activation energies were determined from temperature dependences of the correlation times. Of the three water models considered, SPCE demonstrated the best performance. The results obtained can be helpful for interpretation of experimental temperature dependences of NMR relaxation rates for water molecules confined in porous media with complex topology.

Schiff bases allow the creation of compounds with a wide variety of architectures and properties and have been of interest to researchers for many years. This mini-review describes some of the possibilities of the EPR method, which we use to study Fe(III) complexes with polydentate Schiff bases, many of which have been synthesized for the first time. Obtaining information at the local level using EPR spectroscopy allows us to grasp the molecular structure–property relationship and to adjust the synthesis strategy to create multifunctional substances with predetermined properties.

A more detailed insight into the chemical kinetics and dynamics of chemical exchanges within a molecule or between molecules in liquids is made possible by the NMR CPMG method, which, in addition to the exchange rate, gives its power spectrum, which contains information about the underlying processes of chemical exchange. The applicability of the method is demonstrated by measuring the chemical exchange in an aqueous solutions of sucrose, whose rate spectra have shapes that cannot be explained as transitions in a double potential well, but after interpretation using the chemical Langevin equations, it can be explained as a cascading chemical transition across several intermediate potential walls.

We celebrate 80 years of EPR with a special issue of Applied Magnetic Resonance featuring both reviews and regular research articles. The focus is new opportunities for application of EPR and new directions for development of EPR. This introduction concisely surveys the scope of EPR and hints at future developments.