Phase Transition in Temperature ?Quadrupolar Phase-Disordered Phase? in a Two-Dimensional Non-Heisenberg Ferromagnet

Abstract

Subject classification: 75.30.Kz In the paper we investigate phase transitions in temperature from the quadrupolar phase to the disordered phase in 2D isotropic and anisotropic non-Heisenberg ferromagnets. It is shown that in a 2D isotropic non-Heisenberg ferromagnet the long-range magnetic order is absent, whereas the quadrupolar phase is implemented in the anisotropic one. The temperature of the phase transition is determined. This system is compared with a 3D non-Heisenberg ferromagnet.

Phase states of an S=1 magnet with anisotropic exchange interactions

“…However, as shown in Ref. [23], the QU 2 -phase can be realized in such systems. Hence, we will be interested only in the transition temperature from the QU 2 -phase to the paramagnetic state.…”

“…Before investigating the case of arbitrary values of the exchange anisotropy parameter D, consider the more simple situations: the so-called isotropic exchange case with D ¼ 1, considered, for example, in [9,21,[23][24][25], and also so-called Ising case with D ¼ 0.…”

Сверхтвердая Магнитная Фаза В Двумерном Изингоподобном Антиферромагнетике С Большой Одноионной Анизотропией

“…Что же касается квантовых флукту-аций, то они конечны, поскольку сходимость интеграла флуктуаций для всех однородных состояний обеспечива-ется учетом магнитодипольного взаимодействия [48][49][50][51] и влиянием внешнего магнитного поля. Поэтому тео-рема Мермина−Вагнера о реализации дальнего маг-нитного порядка в двумерных системах не применима для рассматриваемой модели.…”

Influence of Dipole Interaction on the Phase Transitions Due to Temperature Variation in Two-Dimensional Ferromagnets

“…It is somewhat convenient to use the Hubbard operators [17][18][19][20]. Separating the mean field out of the exchange part of the Hamiltonian (11), the single-site Hamiltonian is obtained as…”

“…The denominator of the Green function determines the dispersion equation of coupled ME waves [10,[18][19][20] det kd ij þ x ij k ¼ 0 ; …”