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

摘要

Quantum effects expressed by the energy shift Delta E from the Neel energy E(Neel) and the spin reduction Delta S for zero-point fluctuations of magnons are investigated theoretically for the triangular antiferromagnets (TLAF) on the xy plane with the one-ion-type axial anisotropy -D(S-z)(2). We use a method of constructing the canonical transformation without knowledge of the analytical expression called the Bogoliubov transformation. As a result, boson-type excitations are obtained numerically. Here, characteristic properties are discussed in comparison with those for TLAF with the plane-type anisotropy +D(S-z)(2), for which the canonical transformation can be given in analytical form. Furthermore, the calculation is performed to reveal quantum effects in a six-sublattice structure, which is formed in layered TLAF with the interlayer antiferromagnetic exchange interaction. The behavior of calculated Delta E and Delta S is discussed in the context of magnetic properties of VBr2, VCl2, CsNiBr3, and CsMnI3. [References: 18]