Magnetisation dynamics

The partial recovery of the quantum phase coherence of nuclear dipoles originates from the non-commutative property of the Zeeman energy with the quantum operator which represents the residual interaction after rotating the spins. This rotation has no effect on the magnetisation dynamics when the residual interaction, hHR, is equal to zero. No... 

This effect can in principle be measured by any technique that is sensitive to the magnetisation dynamics and in addition to the SQUID measurements above quantum tunnelling of magnetisation (QTM) has been observed for Mni2 by, for example, torque magnetometry, and Mn nuclear relaxation rates in and specific heat. ... 

This interpretation of the dynamic phenomenon is based on the changes of the frequency of the macroscopic magnetisation vector hence in this form it can be applied to uncoupled spins only. 

Solid-state NMR magnetisation relaxation experiments provide a good method for the analysis of network structures. In the past two decades considerable progress has been made in the field of elastomer characterisation using transverse or spin-spin (T2) relaxation data [36-42]. The principle of the use of such relaxation experiments is based on the high sensitivity of the relaxation process to chain dynamics involving large spatial-scale chain motion in elastomers at temperatures well above the Tg and in swollen networks. Since chain motion is closely coupled to elastomer structure, chemical information can also be obtained in this way. 

Dynamic Order Parameters from 2D 1H Magnetisation Exchange Spectroscopy... 

Dynamic nuclear polarisation (DNP) To increase sensitivity Magnetisation transferred from unpaired electrons to 13C spins via 1H spins if required. Sensitivity improvement of about 100-fold... 

There is also a number of sequences that allow the dynamics to be probed. The CP curve itself can be mapped out by using variable contact time, and fitted to determine Tis and Tip. Other sequences for determining the various relaxation times (X T and Tip, H T and Tip) are shown in Figure 3.27. The H T can be detected via the carbon which sometimes allows the Ti of the different protons to be distinguished. Even if T i is long, it can be determined via the proton magnetisation, provided Ti > > T (Torchia 1978). 

The methods available to determine reaction rates by NMR spectroscopy include line broadening, spin saturation transfer and exchange spectroscopy (EXSY). The latter approach can be completed by both 1 and 2 D procedures. Several studies in the literature have served to illustrate that the dynamic behaviom of complexes detected through the parahydrogen effect can be examined. A general feature of this approach has involved the refocusing of the initial antiphase magnetisation. 

A well-known and important phenomenon in the area of nuclear-spin resonance (NMR) in gases, liquids, or solid samples is dynamic nuclear-spin polarisation (DNP) (see e.g. [M6]). This term refers to deviations of the nuclear magnetisation from its thermal-equilibrium value, thus a deviation from the Boltzmann distribution of the populations of the nuclear Zeeman terms, which is produced by optical pumping (Kastler [31]), by the Overhauser effect [32], or by the effet solide or solid-state effect [33]. In all these cases, the primary effect is a disturbance of the Boltzmann distribution in the electronic-spin system. In the Overhauser effect and the effet solide, this disturbance is caused for example by saturation of an ESR transition. Owing to the hyperfine coupling, a nuclear polarisation then results from coupled nuclear-electronic spin relaxation processes, whereby the polarisation of the electronic spins is transferred to the nuclear spins. 

Many of the specific applications of ferrites depend on their behaviour at high frequencies. When subjected to an ac field, ferrite permeability shows several dispersions as the field frequency increases, the various magnetisation mechanisms become unable to follow the field. The dispersion frequency for each mechanism is different, since they have different time constants. Fig. 4.59. The low-frequency dispersions are associated with domain wall dynamics and the high-frequency dispersion, with spin resonance the latter, usually in the GHz range, is discussed in Section 4.6.2. 

---