Spin accumulation

The D values in Table 4 display some interesting and remarkable trends in the spin-delocalizing ability of the heteroaryl substituents. The three regio-isomeric pyridyl-substituted triplet diradicals 12g ( — 0.01), 12i ( — 0.05), and 12k (—0.06) delocalize spin worse than the phenyl reference system in the order para > ortho > meta phenyl. Especially in the ortho and para isomers delocalization is definitely less effective than for phenyl. Thus, the pyridyl derivatives act as spin donors by enhancing the spin density at the radical site, although the effects are relatively small. The small effects are mainly due to destabilizing aminyl-type radical structures with unfavorable spin accumulation at the nitrogen atom (Fig. 20) [61]. 

Fig. 7.2 Stejskal-Tanner diffusion spin echo sequence [142]. Spins accumulate phase shift during the first gradient pulse. The 180 pulse inverts the phase of all spins. The second gradient lobe induces another phase shift that is effectively opposite to the first gradient pulse due to the effect of the spin echo. The phase shifts are identical in magnitude and cancel each other out. For...

The Concepts of Spin Accumulation and Spin Diffusion Length... 

As a consequence, if a current is passed from such a spin-asymmetric material, for example cobalt, into a paramagnetic material such as silver (which has no spin asymmetry between spin channels), there is a net influx into the silver of up-spins over down-spins. Thus, a surplus of up-spins appears in the silver, and with it a small associated magnetic moment per unit volume. This surplus is known as a spin accumulation. Evidently, for a constant current flow, the spin accumulation cannot increase indefinitely. The spin-up electrons injected across... 

It follows from the above discussion that the spin accumulation decays exponentially away from the interface, on a length scale called the spin diffusion length (A-sd)- This concept is crucial for realizing a link between spin electronics and magnetic nanostructures. In this section, we shall not go further into this concept, but we shall do a rough calculation to see how large Asd is and on what parameters it depends. We use the following expression from [3.90] ... 

The displacement of a spin can be encoded in a manner very similar to that used for the phase encoding of spatial infonnation [28, 29 and 30]. Consider a spin j with position /-(t) moving in a magnetic field gradient G. The accumulated phase, cpj, of the spin at time t is given by... 

Fig. 1.3 Effect of a pulsed magnetic field zero. During the gradient pulse, the field gradient of strength g on the phase of a signal becomes position-dependent and a phase shift contribution originating from spins at position is accumulated that is proportional to t. Prior to the gradient pulse, all spins position t and time t. After the gradient pulse...

Fig. 1.22 RARE sequence. Here the formation of the first spin echo is conventional. The CPMG form of spin echo is used to avoid the accumulation of flip angle errors over the echo train. However, before the second echo can be acquired, the phase-encoding has to be rewound to undo the dephasing of the spins. Therefore, a phase encoding step of equal...

In contrast, for the NO8- species the N—O bond is elongated, only slightly polarized, and the stretching frequency, vNO, decreases below 1850 cm-1. Such changes indicate that the activation consists in redistribution of the electron and spin densities within the M—NO unit, which accumulates on the nitrogen atom. Among the first series TMI, the oxidative adsorption is less common and includes only the tj1 CuNO] 11 and 171 3CrNO 6 adducts. The mechanistic implications of the electronic structures for both type of the nitrosyl complexes are discussed in the next section. 

C) A h NMR spectrum in H20. The resonance frequency was 123.225 MHz, and the signal was accumulated over four times. (D) H spin echoes. 

The new backbone atom must now be checked for overlap with other atoms on the chain. The distance from every other atom is then calculated. If there is a spin on this atom, terms for the second moment summation are accumulated in this program loop as well. 

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