Thermal equilibrium dipolar fields

We will consider dipolar interaction in zero field so that the total Hamiltonian is given by the sum of the anisotropy and dipolar energies = E -TEi. By restricting the calculation of thermal equilibrium properties to the case 1. we can use thermodynamical perturbation theory [27,28] to expand the Boltzmann distribution in powers of This leads to an expression of the form [23]... 

A CaFj crystal is placed in a strong magnetic field B, say in the z-direction. We recall that the F nuclei carry a nuclear spin I = Thermal equilibrium is established /lc = (/<% 0, 0). An RF pulse is then been applied, with the effect -> The time development of the latter is then observed / (/) displays an oscillatory damping to the value j (oo) = 0. This phenomenon has been explained on the basis of the dipolar interactions between the fluorine nuclei. No spin-lattice relaxation need be considered (so that the spin system as such can actually be considered as being isolated). 

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