The hysteresis of acoustic parameters of smectic-C in rotating magnetic field was observed for the h t time. The obtained experimental results are compared with the theory predictions based on the bistability of the orientational structure of smectic-C in a magnetic field.Compared with other smectics the smectic-C phase (Sc) is of special interest because its orientational structure can be altered (rotation of the local C-director or the projection of the director n on the layer plane) easily enough under the action of a moderate magnetic field

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