Presence Of Dipolar Coupling Research Articles

Synthesis of 5‐Cyano‐Tryptophan as a Two‐Dimensional Infrared Spectroscopic Reporter of Structure

AbstractA concise synthesis of protected 5‐cyano‐l‐tryptophan (Trp5CN) has been developed for 2D IR spectroscopic investigations within either peptides or proteins. To assess the potential of differently substituted cyano‐tryptophans, several model cyano‐indole systems were characterized using IR spectroscopy. Upon assessment of their spectroscopic properties, Trp5CN was integrated into a model peptide sequence, Trp5CN‐Gly‐Phe4CN, to elucidate its structure. This peptide demonstrates the capability of this probe to capture structural information by 2D IR spectroscopy. The 2D IR spectrum of the peptide in water was simulated to reveal a unique spectral signature resulting from the presence of dipolar coupling. The coupling strength between cyano labels was determined to be 1.4 cm−1 by matching the slopes along the max contour for the simulated and experimental spectrum. Using transition dipole coupling, a distance between the two probes of 13 Å was calculated.

Synthesis of 5-Cyano-Tryptophan as a Two-Dimensional Infrared Spectroscopic Reporter of Structure.

A concise synthesis of protected 5-cyano-l-tryptophan (Trp5CN ) has been developed for 2D IR spectroscopic investigations within either peptides or proteins. To assess the potential of differently substituted cyano-tryptophans, several model cyano-indole systems were characterized using IR spectroscopy. Upon assessment of their spectroscopic properties, Trp5CN was integrated into a model peptide sequence, Trp5CN -Gly-Phe4CN , to elucidate its structure. This peptide demonstrates the capability of this probe to capture structural information by 2D IR spectroscopy. The 2D IR spectrum of the peptide in water was simulated to reveal a unique spectral signature resulting from the presence of dipolar coupling. The coupling strength between cyano labels was determined to be 1.4 cm-1 by matching the slopes along the max contour for the simulated and experimental spectrum. Using transition dipole coupling, a distance between the two probes of 13 Å was calculated.

Interface and Temperature Dependent Magnetic Properties in Permalloy Thin Films and Tunnel Junction Structures

Magnetization dynamics and field dependent magnetization of different devices based on 25-30 nm thick Permalloy (Py) films: such as single Py layers (Py/MgO; Py/CoFeB/Al2O3) and Py inserted as a magnetic layer in magnetic tunnel junctions (Py/CoFe/Al2O3/CoFe; Py/CoFeB/Al2O3/CoFe; Py/MgO/Fe) have been extensively studied within a temperature range between 300 K down to 5 K. The dynamic response was investigated in the linear regime measuring the ferromagnetic resonance response of the Py layers using broadband vector network analyzer technique. Both the static and the dynamic properties suggest the possible presence of a thermally induced spin reorientation transition in the Py interface at temperatures around 60 K in all the samples investigated. It seems, however, that the details of the interface between Py and the hardening ferromagnet/insulator structure, the atomic structure of Py layers (amorphous vs. textured) as well as the presence of dipolar coupling through the insulating barrier in the magnetic tunnel junction structures could strongly influence this low temperature reorientation transition. Our conclusions are indirectly supported by structural characterization of the samples by means of X-Ray diffraction and high resolution transmission electron microscopy techniques. Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers. Comparison of the simulations with experimental results also shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.

Influence of interlayer dipolar coupling on magnetization reversal and high-frequency dynamics in asymmetric NiFe/Cu/NiFe circular nanorings

The magnetization reversal process and the spectrum of magnetic excitations of NiFe(10 nm)/Cu(10 nm)/NiFe(20 nm) circular nanorings have been investigated by magneto-optic Kerr effect, magnetic force microscopy (MFM), and Brillouin light scattering (BLS). These measurements reveal several magnetic ground states as a function of the applied field strength, corresponding to the different magnetization distributions in the two ferromagnetic layers with switching fields influenced by the sizable interlayer dipolar coupling. A satisfactory reproduction of the measured hysteresis loop as well as of the main features of the MFM images was achieved by the combined use of three-dimensional micromagnetic simulations and analytical calculations of the dipolar stray field felt by the magnetic tip. The spectrum of thermal spin waves reveals the presence of several discrete and stationary modes, whose frequency evolution with the applied field was measured by BLS, encompassing different magnetic ground states. The frequency and the spatial distribution of the dynamical magnetization of each mode were calculated by micromagnetic simulations. The presence of dipolar coupling between the layers causes the appearance of modes, which are either in-phase (acoustic) or out-of-phase (optical) in the two layers, as well as the presence of complicated mode profiles when the ground states in the two layers are different.

Extrinsic contributions to the ferromagnetic resonance response of ultrathin films

We develop a theory of the extrinsic contributions to the ferromagnetic resonance linewidth and frequency shift of ultrathin films. The basic mechanism is two magnon scattering by defects at surfaces and interfaces. In the presence of dipolar couplings between spins in the film, one realizes short wavelength spin waves degenerate with the ferromagnetic resonance (FMR) mode, provided the magnetization is parallel to the film surfaces. Defects on the surface or interface thus scatter the FMR mode into such short wavelength spin waves, producing a dephasing contribution to the linewidth, and a frequency shift of the resonance field. The mechanism described here is inoperative when the magnetization is perpendicular to the film.

Study of anisotropic diffusion of oriented molecules by multiple quantum spin echoes

Experiments have been completed which demonstrate the greatly enhanced sensitivity of the multiple quantum version of the NMR spin echo diffusion experiment. These experiments are particularly well-suited to studies of anisotropic diffusion where the presence of dipolar couplings may make the standard experiment technically infeasible. (AIP)

Magnetic collective excitations in the B phase of superfluid He-3

The dynamical susceptibility of the B phase of superfluid He-3 in the presence of dipolar coupling is calculated in the collisionless regime. Two poles of the susceptibility that correspond to the spin wave and the mode with energy gap (2/5)1/2 2Δ are found. The result agrees with that of Tewordt and Einzel qualitatively and contradicts the recent work by Maki. The residue of the high-frequency mode becomes remarkable near the transition temperature. The dispersion relations of these modes atT=0 K and near the transition temperature are given in the most general form.