Tailored HCCH-TOCSY experiment for resonance assignment in the proximity of a paramagnetic center

The presence of a paramagnetic center may disturb both coherent and incoherent communication between nuclear spins that are affected, to some extent, by the hyperfine interaction. This is a limiting factor to an extensive use of paramagnetic probes in NMR spectroscopy to enhance partial alignment and to exploit cross correlation effects and pseudocontact shifts. We propose here an HCCH-TOCSY experiment tailored to identify spin systems involving resonances that are partly or completely affected by hyperfine interaction. The efficiency of polarization transfer steps when fast relaxing nuclei are involved is discussed. The sequence is tested for the protein Calbindin D(9k), in which one of the two native Ca2+ ions is replaced by the paramagnetic Ce3+ ion as well as for the oxidized form of cytochrome b(562).     

The influence of transverse perturbations on the propagation of picosecond acoustic pulses in a paramagnetic crystal

The influence of transverse perturbations on the dynamics of a picosecond soliton-like acoustic pulse in a paramagnetic crystal in an external magnetic field is investigated. The nonlinear and dispersion effects are governed by the intrinsic properties of the crystal and the spin-phonon interaction. The effect of different nonlinear mechanisms and an external magnetic field on the stability against transverse perturbations is analyzed. It is shown that, in the absence of paramagnetic impurities, there can exist only a compression pulse that propagates in a defocusing regime. In the presence of paramagnetic ions in the crystal, there can arise rarefaction pulses that, under specific conditions, can propagate in self-focusing and self-channeling regimes.     

Polypropylene track membranes as a promising material for targets with polarized protons

Polypropylene track membranes made by irradiation of polypropylene films with a beam of high-energy heavy ions followed by chemical etching of latent ion tracks are proposed for being used as a polarized target material. To give membranes paramagnetic properties needed for allowing dynamic polarization of nuclei, the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl was introduced in the samples by the thermal diffusion technique. Using the electron paramagnetic resonance method, we obtained information on paramagnetic centers in the polymer matrix of the membranes and determined the nitroxyl radical concentration and rotational mobility of the spin probe in them.     

Interaction of separated ferromagnetic domains in a hole-doped manganite achieved by a magnetic field

We report the change in the magnetic microstructure with the application of a magnetic field to a hole-doped manganite La0.81Sr0.19MnO3 in the mixed-phase state, in which ferromagnetic and paramagnetic phases coexist. In situ observations by electron holography have revealed that the applied magnetic field generates a "channel" of the magnetic flux in the paramagnetic phase region, thereby connecting the separated ferromagnetic domains. The magnetic flux density of this channel is estimated at 0.33 T, which is comparable with that of the ferromagnetic domains. The connection of the separated ferromagnetic domains appears to promote the conduction in the mixed-phase state as predicted for many manganites exhibiting the magnetoresistance effect.     

Ferromagnetic clusters induced by a nonmagnetic random disorder in diluted magnetic semiconductors

In this work, we analyze the nonmagnetic random disorder leading to a formation of ferromagnetic clusters in diluted magnetic semiconductors. The nonmagnetic random disorder arises from randomness in the host lattice. Including the disorder to the Kondo lattice model with random distribution of magnetic dopants, the ferromagnetic–paramagnetic transition in the system is investigated in the framework of dynamical mean-field theory. At a certain low temperature one finds a fraction of ferromagnetic sites transiting to the paramagnetic state. Enlarging the nonmagnetic random disorder strength, the paramagnetic regimes expand resulting in the formation of the ferromagnetic clusters.     

Parity-locking effect in a strongly-correlated ring

Orbital magnetism in an integrable model of a multichannel ring with long-ranged electron-electron interactions is investigated. In a noninteracting multichannel system, the response to an external magnetic flux is the sum of many diamagnetic and paramagnetic contributions, but we find that for sufficiently strong correlations, the contributions of all channels add constructively, leading to a parity (diamagnetic or paramagnetic) which depends only on the total number of electrons. Numerical results confirm that this parity-locking effect is robust with respect to subband mixing due to disorder.     

Amplification oand absorption of an electromagnetic wave in a moderating structure with a paramagnetic crystal

Conclusions An analysis of the paramagnetic amplification G_e and absorption L_e of an electromagnetic wave in a moderating structure shows that the effects of saturation in some cases are significantly different. In consequence of this, the saturation threshold in the crystal in the amplification mode is lower than the saturation threshold in the absorption mode approximately by a factor of G_eM/2L_att. This conclusion must be borne in mind when investigating paramagnetic crystals in distributed structures, in particular when investigating the invesion characteristics of potentially active substances for lasers.It follows from the analysis that the investigation of the invesion properties of the crystal must be conducted on small samples of the crystal, as the possible error in measuring the inversion coefficient will be less for lower values of the paramagnetic amplification factor (all conditions being equal).A moderating structure with a radiating paramagnetic crystal is an example of an active medium, in which the wave propagation process can be described and analyzed by means of Eq. (1). As E_p. (1) postulates the solution in analytic form, and all the parameters of the equation have a clear physical meaning and can be monitored easily during the experimental investigation, then the structure considered here obviously can be a suitable model for studying the propagation of waves in other active media (see, e. g., [9]).Institute of Radiophysics and Electronics, Academy of Sciences of the Ukrainian SSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 22, No. 7, pp. 819–825, July, 1979.     

Depolarized Light Scattering from Paramagnetic Liquids in a Magnetic Field

In order to identify spectral features and molecular movement types the magnetic field's influence on rotational and diffuse shear modes of paramagnetic liquids is analysed. Consideration of the corresponding changes in depolarized (VH) light scattering spectra illustrates a systematic method of studying both paramagnetic and diamagnetic liquids.     

Triplet exciton and ferromagnetic instability of a two-dimensional electron gas in a large magnetic field with filling factor v=2

We have investigated the phase diagram of a two-dimensional electron gas in a large magnetic field as a function of the difference between the cyclotron and the spin resonance splittings. For suitable values of this difference we find that when the two spin states of the lowest Landau level are fully occupied the paramagnetic ground state suffers a triplet exciton (spin-density-wave) instability. However our analysis shows that in the simplest case such an instability is preempted by a paramagnetic to ferromagnetic phase transition. The occurence of this transition and some of its consequences have been studied.     

Instability of Fabry-Perot interferometer with a multilayered paramagnetic filling

The results of the analysis of the stability of stationary solutions of wave equations discribing a behavior of the nonlinear Fabry-Perot interferometer with a saturated paramagnetic filling are presented in this paper. The cases when paramagnetic medium is characterized by a homogeneously and nonhomogeneously broadened line of the magnetic resonance have been considered. Areas of unstable behavior of these characteristics of the resonance structure have been found.     

Discovery of a self-trapped-electron center in α-TeO 2

Electron spin resonance (ESR) studies show that electron irradiation of an f -TeO 2 single crystal followed by 330-nm UV illumination at ～10 v K generates a new spin-1/2 paramagnetic center having C 2 symmetry, like the Te lattice sites, that is attributed to a self-trapped charge on a Te. Identification is facilitated by a strong hyperfine interaction with 125 Te at a central Te site and weaker 125 Te superhyperfine interactions with three different equivalent pairs of neighboring Te cations. The irradiations also produce the diamagnetic V_{O}^{\times} center and the paramagnetic V_{O}^{\bullet} and V_{O}^{\prime} centers. From measurements of concentration changes of the paramagnetic centers due to thermal annealing of the new center it is deduced that the self-trapped charge is a self-trapped electron. It is designated as a \hbox{TeO}_{2}^{\prime} center. This assignment is consistent with its low thermal stability since it anneals quickly at temperatures above 40 v K. ESR characteristics of this new center are described.     

Spin wave-like excitation of magnetization fluctuations in the vicinity of the phase transition from a paramagnetic phase to a ferromagnetic phase with domain structure

The dynamics of fluctuations in ferromagnetic samples with finite dimension has been described. There are solutions of equations of motion describing spin waves of magnetization fluctuations in the paramagnetic phase. The analysis of the dispersion relation describing the soft mode of spin waves allows us to determine the phase transition temperature from a paramagnetic phase to a ferromagnetic one with domain structure.     

A fractal approach to the distribution function of a paramagnetic system

A similarity between the random walk problem and a paramagnetic system has been established. The distribution functions of the stationary states have been obtained by making the Tsallis entropy a maximum, belonging to the statistical ensemble of a paramagnetic system, under suitable constraints using the variational methods. The asymptotic form of the distribution of the magnetic moments has been determined from the behaviour of the Lévy distribution. For the paramagnetic system which has been considered as the fractally structured system, following the way used by Alemany and Zanette [1] Tsallisq index has been related to the fractal dimension and the interval of the values ofq has also been determined.     

EPR spectra of a GdMnO3 thin film on a SrTiO3 substrate

Electron paramagnetic resonance (EPR) spectra of a GdMnO₃/SrTiO₃ thin film in the X band have been measured in the temperature interval from 200 to 450 K. Signals from two types of paramagnetic centers have been observed in the spectra. The first paramagnetic center is a subsystem of Gd³⁺ ions, in the EPR spectrum of which the fine structure lines are resolved below 350 K. The second paramagnetic center is a system of manganese and gadolinium ions, in the EPR spectrum of which an exchange-narrowed line is observed with the width ΔH several times less than the width ΔH of an exchange-narrowed line observed in the GdMnO₃ single crystal. Unusual magnetic properties are due to the mismatch of the lattice parameters of the GdMnO₃ thin film and the SrTiO₃ substrate.     

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1rho can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields by MRI. However, the in vivo detectable dimension for labeled cell clusters/tissues in T1rho-weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide sub-millimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment, and intravascular agents (Gd-DTPA)30-BSA were administrated into the compartment via bolus injections. Both in vitro and in vivo results demonstrate that the paramagnetic relaxation enhancement is predominant in the T1rho-weighted image in the presence of water diffusion-exchange. The T1rho contrast has substantially higher sensitivity than the conventional T1 contrast in detecting paramagnetic agents, especially at low paramagnetic agent volumetric fractions, low paramagnetic agent concentrations, and low RF amplitudes. Short pulse duration, short pulse recycle delay and efficient paramagnetic relaxation can reduce the influence of water diffusion-exchange on the paramagnetic enhancement. This study paves the way for the design of off-resonance rotating experiments to detect labeled cell clusters/tissue compartments in vivo at a sub-millimeter scale.     

Dynamics of paramagnetic agents by off-resonance rotating frame technique in the presence of magnetization transfer effect

The simple method for measuring the rotational correlation time of paramagnetic ion chelates via off-resonance rotating frame technique is challenged in vivo by the magnetization transfer effect. A theoretical model for the spin relaxation of water protons in the presence of paramagnetic ion chelates and magnetization transfer effect is described. This model considers the competitive relaxations of water protons by the paramagnetic relaxation pathway and the magnetization transfer pathway. The influence of magnetization transfer on the total residual z-magnetization has been quantitatively evaluated in the context of the magnetization map and various difference magnetization profiles for the macromolecule conjugated Gd-DTPA in cross-linked protein gels. The numerical simulations and experimental validations confirm that the rotational correlation time for the paramagnetic ion chelates can be measured even in the presence of strong magnetization transfer. This spin relaxation model also provides novel approaches to enhance the detection sensitivity for paramagnetic labeling by suppressing the spin relaxations caused by the magnetization transfer. The inclusion of the magnetization transfer effect allows us to use the magnetization map as a simulation tool to design efficient paramagnetic labeling targeting at specific tissues, to design experiments running at low RF power depositions, and to optimize the sensitivity for detecting paramagnetic labeling. Thus, the presented method will be a very useful tool for the in vivo applications such as molecular imaging via paramagnetic labeling.     

Stationary and high-frequency pulsed electron paramagnetic resonance of a calcified atherosclerotic plaque

New possibilities of applying high-frequency electron paramagnetic resonance in medicine are demonstrated on an example of the investigation of a calcified atherosclerotic plaque. After the irradiation of the atherosclerotic plaque by x rays, a new type of paramagnetic centers—organomineral radicals—is detected. The spectral and relaxation characteristics of these radicals depend on the calcification degree of the atherosclerotic plaque and can be used for diagnostics.     

Paramagnetic intrinsic Meissner effect in a bulk

We calculate the free energy of a quasi-two-dimensional (Q2D) superconductor with ξ_⊥ < d in a parallel magnetic field, where ξ_⊥ is a perpendicular to the conducting layer coherence length and d is the interlayer distance. It is shown to be different from that in the famous Lawrence-Doniach model. In particular, at high enough magnetic fields, the Meissner currents are found to create an unexpected paramagnetic moment due to the shrinking of the Cooper pairs “sizes” in a direction perpendicular to the conducting layers. We suggest measuring this paramagnetic intrinsic Meissner effect in Q2D superconductors and superconducting superlattices. The text was submitted by the author in English.     

Spin density wave in oxypnictide superconductors in a three-band model

The spin density wave and its temperature dependence in oxypnictide are studied in a three-band model. The spin susceptibilities with various interactions are calculated in the random phase approximation (PPA). It is found that the spin susceptibility peaks around the M point show a spin density wave (SDW) with momentum (0, π) and a clear stripe-like spin configuration. The intra-band Coulomb repulsion enhances remarkably the SDW but the Hund’s coupling weakens it. It is shown that a new resonance appears at higher temperatures at the Γ point indicating the formation of a paramagnetic phase. There is a clear transition from the SDW phase to the paramagnetic phase.