THEORETICAL-STUDY ON QUANTUM EFFECTS IN TRIANGULAR ANTIFERROMAGNETS WITH AXIAL ANISOTROPY USING THE NUMERICALLY CONSTRUCTED BOGOLIUBOV TRANSFORMATION FOR MAGNONS

Quantum effects expressed by the energy shift Delta E from the Neel en ergy E(Neel) and the spin reduction Delta S for zero-point fluctuation s of magnons are investigated theoretically for the triangular antifer romagnets (TLAF) on the xy plane with the one-ion-type axial anisotrop y -\D\(S-z)(2). We use a method of constructing the canonical transfor mation without knowledge of the analytical expression called the Bogol iubov transformation. As a result, boson-type excitations are obtained numerically. Here, characteristic properties are discussed in compari son with those for TLAF with the plane-type anisotropy +\D\(S-z)(2), f or which the canonical transformation can be given in analytical form. Furthermore, the calculation is performed to reveal quantum effects i n a six-sublattice structure, which is formed in layered TLAF with the interlayer antiferromagnetic exchange interaction. The behavior of ca lculated Delta E and Delta S is discussed in the context of magnetic p roperties of VBr2, VCl2, CsNiBr3, and CsMnI3.