Abstract: | The periodic deformations induced by external fields have been analysed by means of the Taylor expansion method based on the theorems of catastrophe theory. The analysis is restricted to the planar nematic slab influenced by a magnetic field. Two different configurations of the field which lead to periodic deformations with prevailing splay or twist we considered. The ranges of material constants at which the periodic state is stable and the threshold magnetic field strength have been found. The problem of transitions between the undeformed, uniformly deformed and periodic states is discussed. |