Pulsed magnet

There are a number of NMR methods available for evaluation of self-diffusion coefficients, all of which use the same basic measurement principle [60]. Namely, they are all based on the application of the spin-echo technique under conditions of either a static or a pulsed magnetic field gradient. Essentially, a spin-echo pulse sequence is applied to a nucleus in the ion of interest while at the same time a constant or pulsed field gradient is applied to the nucleus. The spin echo of this nucleus is then measured and its attenuation due to the diffusion of the nucleus in the field gradient is used to determine its self-diffusion coefficient. The self-diffusion coefficient data for a variety of ionic liquids are given in Table 3.6-6. 

Saarinen, TR Woodward, WS, Computer-Controlled Pulsed Magnetic Field Gradient NMR System for Electrophoretic Mobility Measurements, Reviews of Scientific Instruments 59, 761, 1988. 

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...

A much simpler and more flexible approach, however, extends the scheme of pulsed magnetic field gradients discussed above to include more complex time dependences. To see how this can be done, we write down the general dependence of the phase shift accumulated at time t subject to a space-dependent Larmor frequency ... 

Coulton, L.A. and A.T. Barker. 1991. The effect of low-frequency pulsed magnetic fields on chick embryonic... 

Fig. 10.4 Experimental scheme for the 2D [ N. HJ-TROSY using single transition to single transition polarization transfer (box labeled ST2-PT). On the lines marked H and 15N, narrow and wide bars stand for nonselective 90° and 180° radio-frequency pulses, respectively. The delay t=2.7 ms (see text). The line marked PFG indicates the pulsed magnetic field gradients applied along the z-axis G, amplitude 30 G/cm, duration 1 ms G2, 40 G/cm, 1 ms G3, 40 G/cm, 1 ms ...

If very high fields are required then one alternative apart from Bitter magnets, is to use pulse magnets and the Kobe facility has recently been described, which provides up to 36 T pulse field combined with a range of sources that extend from 110 GHz to 3 THz.102... 

When pulsed magnetic field gradients are applied to study diffusive processes, the MR technique is often referred to as pulsed field gradient or pulsed gradient spin echo (PGSE) MR. Application of PGSE MR techniques to quantify molecular diffusion was pioneered by Stejskal and Tanner 17,18), and the techniques typically probe molecular displacements of 10 -10 m over time scales of the order 10 M s. 

Transport measurements performed using pulsed magnetic field gradients are most clearly understood in the context of a more mathematical framework. It follows from Eq. (2) that the phase shift (i.e., the instantaneous phase offset in resonance frequency) (f) t) acquired (in the rotating frame) following application of... 

Kadomtseva et al. (2000) measured thermal expansion and longitudinal and transverse magnetostriction in pulsed magnetic fields up to 25 T in Lai - Sr MnOj single crystals (x = 0.1,0.125 and 0.15). The results were ascribed to a suppression of the O phase and field-induced transitions to a new orbital-ordered ferromagnetic state. 

Tollner, E.W. and Hung, Y.C. 1992. Low resolution pulse magnetic resonance for measuring moisture in selected grains and kernels. J. Agric. Eng. Res. 53 195-208. 

The results of Zupancic, et.al. (15), are also relevent here. Zupancic investigated diffusion of butane in linear polyethylene using pulsed magnetic field gradient... 

The ESR experiments were performed in the high magnetic field laboratory at the University of Frankfurt [3], The spectrum of magnetic excitations were studied in the 27-200 GHz frequency range in pulsed magnetic fields up to 50 T. 

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