Magnetic fluctuations

For liquids, the dominant relaxation mechanism is the nuclear-nuclear dipole interaction, in which simple motion of one nucleus with respect to the other is the most common source of relaxation [12, 27]. In the gas phase, however, the physical mechanism of relaxation is often quite different. For gases such as the ones listed above, the dominant mechanism is the spin-rotation interaction, in which molecular collisions alter the rotational state of the molecule, leading to rotation-induced magnetic fluctuations that cause relaxation [27]. The equation governing spin-rotation relaxation is given by... 

When the anisotropy energy is large enough it prevents any precession of the magnetic moment of super-paramagnetic crystals. The magnetic fluctuations then arise from the jumps of the moment between different easy directions. The precession prohibition is introduced into the Freed equations in order to meet that requirement every time the electron Larmor precession frequency appears in the equations, it is set to zero 12). 

With 0 3)h QED the major difference emerges from the effective photon bunching or interactions that can result in a photon loop, composed of an 4 photon and an photon. This loop will be associated with a quanta of field. Equation (149) illustrates how this fluctuation in the 4(l and 4(2) potentials are associated with this magnetic fluctuation. The other renormalization techniques in U(l) QED still apply, and are demonstrated below, and the renormalization of divergences associated with the Bii] magnetic fluctuation is also illustrated. 

J. Rossat-Mignod et al., in G. Reiter, P. Horsch, G.C. Psaltakis (Eds), Dynamics of Magnetic Fluctuations in High-Temperature Superconductors, Plenum, New York, 1991. 

If ever needed, it is trivial to add magnetic-fluctuation terms to all these point-particle results. 

The existence of a finite interchain interaction in a quasi-one-dimen-sional system is a prerequisite for a phase transition. However, there exists no necessary relation between the strengths of intra- and interchain couplings. It is thus conceivable to observe for SDW and SC instabilities the existence (if not the predominance) of magnetic fluctuations above the superconducting transition or the reverse as well. Such situations are encountered in the study of the (TMTSF)2X series. 

The period of magnetic fluctuations due to Earth s intrinsic field is not regular but has been shown to have increased over the past 2 X 10" yr. Fluctuations in the past are also recorded and clearly evident in the changing magnetic polarity of Earth over time. 

S-Q-U-I-D, Malcolm said, adjusting the wires. Stands for superconducting quantum interference device. It should be sensitive to tiny magnetic fluctuations in your brain. We re going to hook it to an electronic signal processor that can focus on any selected brain frequency, so we ll be able to lift a few memories from your brain s electrical and magnetic traffic flow. ... 

The second-order magnetic transition is usually preceded by local (short-range) magnetic order. As mentioned in sect. 3 the mean-field theory, which does not take into account the magnetic fluctuations, predicts a jump of AC, = 12.5 J mol K at Tq for a spin 1/2. In this region there are some examples of a practically pure second-... 

The Schottky-like anomaly observed in the specific heat of the compounds discussed in this section can be derived phenomenologically using (a) the resonance-level model, (b) the spin glass behaviour, (c) the crystal field (Schottky) contribution or even (d) low-dimensional magnetic fluctuations. The cases where an HF behaviour is deduced from a large value will be discussed in sect. 9, in connection with the contribution to of the excited crystal field levels. It is clear that complementary techniques, such as NMR, AC susceptibility and electrical resistivity, can easily reveal the magnetic character of the microscopic interactions. In some of the HF compounds the ratio between the y term and the (( -> 0) = Xo value of the susceptibility, and between the / term and the coefficient of the resistivity. A, have values predicted by... 

The conditions required in order to obtain NMR resonances, which are not broadened beyond detection, are given in sect. 4.21. These amount to situations where the magnetic fluctuations due to the unpaired electron (which has a magnetic moment about 10 that of an atomic nucleus) are sufficiently fast for the nuclear-spin transitions to be affected only by an average field. 

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