We present a Landau-type semiphenomenological theory for the zero-sound dispersion relation in normal-liquid-3He films in the presence of a magnetic field or for partially polarized films. We express our result in terms of the spin-dependent (F0a) and spin-independent (F0s) first Landau parameters. We give the zero-field result and the lowest-field correction. We find that the field effect should be readily observable for the presumably attainable experimental accuracy.
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