Theory

Abstract

In many paramagnetic crystals the resonance absorption of microwaves in the presence of a transverse magnetic field spreads over a range of a few hundred gauss, and this can be accounted for by the magnetic interaction between the ions. There are certain substances, however, of which copper sulphate is an example, in which the resonance is sharper than can be explained in this way, and it has been suggested that the sharpness is due to electron exchange¹. Gorter and Van Vleck² have reported the result of a calculation which shows that, while the mean square spread is unaffected by exchange, the mean fourth power spread is increased, indicating a sharpening of the peak together with an enhanced absorption in the wings of the resonance. That such an effect is to be expected can be seen from the following qualitative argument.