Long-period incommensurate structures in crystals with triangular arrangement of magnetic ions

The possibility of formation of a long-period structure in crystals with tr iangular arrangement of magnetic atoms is considered. It is shown that two cycloid and one spiral structures are formed. The influence of a magnetic f ield and second-order magnetic crystallographic anisotropy is studied. Supe rstructures can be transformed into one another by turning the plane of irr educible vectors for which "anticentrifugal" effect takes place, and an int ermediate structure called a "rotating skew spiral" (R (S) over tilde (S) o ver tilde) is formed. It is also shown that "domains" over whose length irr educible vectors turn through an angle of pi/2 can emerge in the system. Th ese "domains" can form structures with a jump in the phase of irreducible v ectors at the boundary. (C) 1999 American Institute of Physics. [S1063-777X (99)00506-X].