Applied Magnetic Resonance最新文献

The quest to enhance the sensitivity of electron spin resonance (ESR) is an ongoing challenge. One potential strategy involves increasing the frequency, for instance, moving from Q-band (approximately 35 GHz) to W-band (approximately 94 GHz). However, this shift typically results in higher transmission and switching losses, as well as increased noise in signal amplifiers. In this work, we address these shortcomings by employing a W-band probehead integrated with a cryogenic low-noise amplifier (LNA) and a microresonator. This configuration allows us to position the LNA close to the resonator, thereby amplifying the acquired ESR signal with minimal losses. Furthermore, when operated at cryogenic temperatures, the LNA exhibits unparalleled noise levels that are significantly lower than those of conventional room temperature LNAs. We detail the novel probehead design and provide some experimental results at room temperature as well as cryogenic temperatures for representative paramagnetic samples. We find, for example, that spin sensitivity of ~ 3 × 10⁵ spins/√Hz is achieved for a sample of phosphorus doped ²⁸Si, even for sub-optimal sample geometry with potential improvement to < 10³ spins/√Hz in more optimal scenarios.

The negatively charged boron vacancy (({text{V}}_{text{B}}^{-})) in hexagonal boron nitride (hBN) is currently considered an intriguing quantum object for testing and developing quantum technologies on two-dimensional van der Waals materials. This article presents results from photoinduced electron spin echo (ESE)-detected electron spin resonance (ESR) and electron–nuclear double-resonance (ENDOR) spectroscopy at the W-band (ν = 94 GHz), focusing on the interactions of the ({text{V}}_{text{B}}^{-}) electron spin with the three nearest nitrogen nuclei (¹⁴N, I = 1). The lines in the ENDOR spectrum are due to both hyperfine and quadrupole interactions for M_S = ± 1 levels and only quadrupole interactions for M_S = 0 levels. We show that significant hyperfine interaction with the three nearest nitrogen atoms, despite the high magnetic field, results in a mixing of the hyperfine sublevels for M_S = 0. We show that significant hyperfine interaction with the three nearest nitrogen atoms, despite the high magnetic field, results in mixing of the hyperfine sublevels. This mixing shifts the ¹⁴N Larmor frequency from its nominal value defined as ({{varvec{nu}}}_{{varvec{L}}}=boldsymbol{ }{{varvec{g}}}_{{varvec{N}}}{{varvec{mu}}}_{{varvec{N}}}{varvec{B}}/{varvec{h}}). This shift observed through ENDOR experiments can be understood using spin-Hamiltonian formalism within the second-order perturbation theory. These findings enhance an understanding of electron–nuclear interactions in hBN.

EPR applications have evolved continuously with the development of the EPR technique. Since 1967, Bruker EPR is constantly developing its products to keep pace with these constantly changing demands. This article presents commercial EPR solutions in perspective of the past, present, and future.

This work addresses the development of a custom-made home-built rapid freeze–quench (RFQ) device and the comparison of its performance to the one of a commercial RFQ setup that was in-house custom adapted. Both systems consist of two syringes that push the reactants into a mixing chamber and the products to a subsequent freezing setup. Using the binding of azide to myoglobin as a calibration reaction, the quenching times of the different setups were compared, evaluating different instrumental parameters, such as software-controlled variation of the aging time, variations of the flow rate and variations of the distance travelled by the mixed sample before freezing. In addition to minimal sample consumption, the home-built RFQ device was found to lead to the shorter reaction times which could be controlled in a time range from 10 to 25 ms. The commercial RFQ system yielded optimal reaction control in a time range from 50 to 200 ms, although a larger volume of reactants needed to be used due to the significant dead volume of the system. Three different freezing methods were also evaluated, among which, in our hands, freezing the jet directly in a deep bath of cold isopentane yielded shorter and reproducible freezing times.

The electron paramagnetic resonance (EPR) g factors and the local structures of Mo⁵⁺ centers on the substitutional and interstitial sites in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d¹ ion in rhombically compressed and elongated octahedra, respectively. In the calculation formulas, the crystal field parameters are determined from the superposition model, and the contributions from the spin–orbit coupling (SOC) of the ligands are taken into account. Based on the calculations, the ligand octahedron in the substitutional Mo⁵⁺ center may suffer a larger axial compression with the parallel and perpendicular impurity—ligand length bonds R′_||s ≈ 1.932 and R′_⊥s ≈ 1.975 Å) than the bond lengths R_||s ≈ 1.99 and R_⊥s ≈ 1.94 Å in the host and the much smaller perpendicular distortion (i.e., θ_s′ ≈ 87.32º) than that θ_s ≈ 81.21º) in the host related to the ideal angle θ₀ ≈ 90º in a regular octahedron due to the Jahn–Teller (JT) effect. For the interstitial Mo⁵⁺ center, the ligand octahedron exhibits the axial elongation (i.e., R′_||i ≈ 2.155 and R′_⊥i ≈ 1.987 Å) rather than a compressed octahedra with R_||i ≈ 1.67 and R_⊥i ≈ 2.23 Å in the host and a smaller rhombic distortion (θ_i′ ≈ 95.2º) than that θ_i ≈ 97º in the host related to θ₀ due to the JT effect. The reasonableness of these results are discussed.

The observation of the exchange narrowing effect is a routine event in EPR spectroscopy. In this paper, I want to draw attention to the fact that every time we observe an exchange narrowing of the EPR spectrum, we have a gas of identical bosons, where the prerequisites of BEC formation are satisfied at room temperature. Imagine the possibility to create BEC without the need to cooling down to nano Kelvin temperatures to get a gas of identical bosons because the phenomenon of exchange narrowing of the EPR spectrum can be easily observed at room temperatures. This article provides a detailed explanation of how a gas of identical bosons can be formed at room temperature in dilute solutions of paramagnetic particles with a discrete EPR spectrum of individual particles. There are still many questions about the Bose–Einstein condensation of a spin polariton gas, which is created under conditions of exchange narrowing of EPR spectra. With the expectation of obtaining additional information about the condensation of bosons in the situation under consideration, this article proposes the protocol of one EPR experiment to prove that the effect of exchange narrowing of EPR spectra can be instrumental in creating BEC in dilute solutions at room temperature.

The study of continuous wave (cw) electron paramagnetic resonance (EPR) spectra still poses a challenge for very broad signals, especially when the spectrum extends over a large part of the accessible field range. The difficulties derive from instrumental challenges, because of insufficient modulation depth and the need to apply measurement conditions that enhance cavity background. The biggest problem, however, is how to define a baseline such that spectral distortions are minimized. Conventional methods rely on a suitable choice of points outside the range of the signal of interest to perform a polynomial interpolation. These methods are effective in most cases where the signal of interest comprises only a narrow range of magnetic field (narrow features). In this study, a novel method of baseline correction for broad signals is proposed and compared to conventional methods. It takes into account that there are only few anchor points for the baseline. The method is applied to the signal of the iron-storage protein ferritin. The ferritin signal is a broad band that extends from zero to 0.8 T. An approach is developed by which this broad signal is analyzed reliably. The method is also extended to the case where the broad signal is superimposed on narrow signals and enables to extract the parameters of both types of signals in a fitting pipeline.