Applied Magnetic Resonance最新文献

Gilbert damping in symmetric Cu/Co/Cu and asymmetric Cu/Co/W multilayers was studied as a function of Co thickness using FMR linewidth measurements. W-capped multilayers showed higher intrinsic damping across all thicknesses, due to strong SOC in W, which enhances spin-pumping, and MDL formation at the Co/W interface, increasing spin-flip scattering. The higher spin-mixing conductance in W-capped multilayers is linked to stronger SOC and enhanced orbital hybridization at the Co/W interface. X-ray diffraction revealed an fcc(111) phase in Co layers up to 4 nm thick, with thicker films showing a mix of fcc(111) and hcp(0001) textures. The Co thin films showed saturation magnetizations near literature values. No dead layer was found in Cu-capped multilayers, however, a 0.3 nm MDL formed in W-capped multilayers due to atomic intermixing at the Co/W interface. FM/NM interfaces are crucial in generating and dissipating pure spin currents, and they significantly impact the damping properties through the influence of seed and capping layers.

Manganese(III) (3d⁴, S = 2) coordination complexes have been widely studied by high-frequency and -field EPR (HFEPR) for their own inherent chemical interest and for providing information for the burgeoning area of molecular magnetism. In the present study, we demonstrate how a stable, easily handled complex of Mn^III, [MnLKNO₃], where L³⁻ is a hexadentate tripodal ligand, trianion of 1,1,1-tris[(3- methoxysalicylideneamino)methyl]ethane, can be used for another purpose entirely. This purpose is as a field and frequency standard for HFEPR that is superior to a “traditional” standard such as an organic radical (e.g., DPPH) with its single, g = 2.00 signal, or to atomic hydrogen, which is less readily available than DPPH and provides only two signals for calibration purposes (Stoll et al. in J Magn Reson 207:158–163, 2010). By contrast, polycrystalline [MnLKNO₃] (1) orients in the external magnetic field of an HFEPR spectrometer (three different spectrometers were employed in this study). The crystal structure of 1 allows determination of the exact, reproducible molecular orientation of 1 in the applied field. This phenomenon provides multiple, well-defined resonances over a broad field sweep range (0–36 T) at any of a wide range of frequencies (tested up to 1 THz so far) allowing accurate calibration of magnetic field in a multi-frequency HFEPR study.

Triarylmethyl (TAM) radicals and TAM-based biradicals are often used as spin labels in different applications. Pulsed dipolar spectroscopy (PDS) is developed for studying interspin distances in the important nanoscale range. Here, we describe synthesis of bis-triarylmethyl biradical and its study using a simple PDS approach based on two-pulse electron spin echo (2p ESE) spectroscopy. It is shown that despite the well-known problems of dead time, interference of electron–nuclear interactions, and fast signal decay, this approach can provide reliable information for the interspin distances. In this approach, strong dipole–dipole coupling can be easily accounted for in the data analysis.

Lithium-ion batteries (LiB) function because of interconnected chemical and physical reactions across a wide range of size scales—from the overlap of atomic orbitals to flexing of the “lattice” upon lithiation/delithiation to the size/morphology of the particles that make up an electrode film. The cathode electrode in a LiB is based on very high concentrations of transition metals like Fe, Co, and Ni with unique unpaired electron spin environments. Further complexity results from changes to the number of unpaired spins available via redox chemistry, and three-dimensional interactions between spin centers through the lattice. These longer range interactions include ferromagnetic/ferrimagnetic/antiferromagnetic ordering, super-exchange, and the presence of magnetic polarons. Thus, while LiB are commonly viewed first as electrochemical in nature, their magnetic nature is just as important to consider, and their performance and state of health should be interpreted in terms of magnetic changes in the material. We have previously observed fully constructed, commercial 18650 NCA, LCO, and LPO batteries have characteristic magnetic fields up to several hundred micro-Tesla, and this measured field changes in response to different SOH or SOC conditions of the cell. That such a strong magnetic field can be measured is both amazing and very surprising. In this review, we will explore LiB magnetic characterization across all size scales by reflecting on advances in SQUID magnetometry, NMR, EPR, and operando magnetometry. We make a first attempt at answering the question of why there is such a strong magnetic signal to measure on commercial LiB. Understanding the effect of a rich unpaired spin environment across size scales will undoubtedly lead to a better understanding of LiB function and may give insight to improved manufacturing approaches and longer use lifetimes. On the 80th anniversary of Zavoisky’s discovery of EPR, we consider the cathode materials of LiB a “symphony of unpaired electrons” and see that advances in EPR, NMR, and magnetometry are needed now more than ever to understand our technologically complex world.

We report the synthesis and EPR and quantum chemical study of a new nitronyl nitroxyl diradical with a pyrene backbone. EPR at the X- and Q-bands indicates weak dipolar coupling between electron spins, the magnitude of which is comparable to hyperfine interactions in nitronyl nitroxide moieties. Quantum chemical calculations predict weak ferromagnetic interaction between radical fragments, which is nevertheless large on the EPR scale. Using additional Q-band measurements on the reference monoradical to accurately determine the g- and A-tensor components and results of quantum chemical calculations, the X/Q-band spectra of the diradical were satisfactorily modelled using a D-value of 82 MHz. The spectroscopic information obtained can be useful in the design of polyradical systems with similar backbones.

In this article we provide an overview of chip-integrated voltage-controlled oscillator (VCO)-based EPR detection as a new paradigm in EPR sensing. After a brief motivation for this alternative detection method, we provide a self-contained overview of the detection principle, both for continuous-wave and pulsed detection. Based on this introduction, we will highlight the advantages and disadvantages of VCO-based detection compared to conventional resonator-based detection. This is followed by an overview of the current state of the art in VCO-based EPR and interesting emerging applications of the technology. The paper concludes with a brief summary and outlook on future research directions.

The problem of renormalization of the spin–orbit interaction operator of electrons of partially filled nf-shells due to exchange-covalent bonds with surrounding ligands has been solved. It is found that along with the change of the standard spin–orbit interaction parameter, new energy operators are generated, which can be interpreted as a spin-dependent crystal field operator. Simple formulas are obtained that allows to calculate its parameters via covalence parameters and overlap integrals. Numerical evaluations have been performed for multiplets (Tb^{3 + } (f^{8} ){}^{7}F_{6}) and (Er^{3 + } (f^{11} ){}^{4}I_{15/2}) in fluorides with cubic symmetry. Calculated parameters were found to be of the order of 10% relative to the standard crystal field parameters.

The development of magnetic resonance methods (ESR, NMR, and FMR), which took place on a global scale after the discovery of the magnetic resonance effect in the 1940s, began to have a significant impact on research in the chemical and physical sciences in Czechoslovakia in the 1950s. Over the years, several laboratories were established at universities and workplaces of Academy of Sciences, using resonance methods to solve problems of a predominantly chemical nature. In addition to NMR spectroscopy, the application of resonance methods to the investigation of paramagnetic particles, mainly free radicals and transition metal complexes, has become prominent. An essential factor in the development of ESR spectroscopy was the gradual improvement in the quality of the instrumentation available in the second half of the 1960s, mainly through the purchase of commercial spectrometers (Varian, Bruker, JEOL). This trend has continued to the present day. The submitted paper is based on the information obtained from people in various departments who have been active or are still active in ESR spectroscopy. At the same time, the contributions of several researchers who are no longer alive are mentioned. In 1993, Czechoslovakia was divided into the Czech and Slovak Republics. This article primarily describes the history of the development of ESR spectroscopy in the present Czech Republic. At the same time, it should be mentioned that the friendly cooperation between Czech and Slovak ESR workplaces continues to benefit both sides.

Oil asphaltenes are known as the cholesterol of petroleum because of their ability to precipitate, deposit, and interrupt the continuous production of oil from underground reservoirs. Studies of asphaltenes by various analytical techniques allow fundamental understanding of their structure for optimizing the processes of geologic exploration and enhanced oil recovery. The purpose of this work is to analyze the temperature dependences of the electron relaxation times of the intrinsic for oil asphaltenes paramagnetic vanadyl-porphyrin (VP) complexes. Asphaltenes from the viscous Ashalcha oil (2500 mPa·s) were investigated using pulsed electron paramagnetic resonance (EPR) techniques at X-band (9 GHz) in the temperature range T = 10–300 K. It is found that at T > 100 K electron spin–lattice (longitudinal) relaxation rate obeys the power law Tⁿ with n ≈ 3.0 while at T < 100 K direct relaxation process is more effective. An attempt to describe the relaxation data in the frameworks of the solid-state Debye model and fractal model are done. These models have little applicability to the type of asphaltenes studied.