Effect of Pressure on Magnetic States of Easy-Plane Antiferromagnets

Abstract

The phase II -P-$ diagram of an easy-plane strongly anisotropic antiferromagnet is studied. It is shown that in such a system a realization of the phase with the nonmagnetic order parameter, the so-called quadruple phase, is possible. The realization of this phase is caused by several purely quantum effects, moreover the mechanism of its appearance differs in principle from that of the antiferromagnet or ferromagnet. The possibility of the disappearance of the angular phase (the so-called quadruple ferromagnetic phase) is also shown.

The Phase Diagram of Two-Axis Ferromagnet and Spectra of Coupled Magnetoelastic Waves

“…As it was shown in papers [3,4,8], when the energy of OA is comparable with the exchange energy, the existence of new phases with a tensorial order parameter is possible. At fields Hc 2 and Hc3 there occurs the OPT from the quadrupolar-under QU-phase characterized by the tensorial order parameter, to the quadrupolar-ferromagnetic (QFM) (angular), and from QFM to FM, in which the magnetic moment is directed along the field.…”

“…reen's function of a λ-polarized phonon with the dispersion law Wλ(k) = ca k, ca is the sound velocity, and columns A" , Bαi have the form The functions 71(11)(α) are determined by the relation of the spin operators with the Hubbard operators [6], and have the form (see (7)):…”

“…In this case (see, for example, [3,4,8]) the manifestation of quantum effects, such as "quantum reduction of spin" is possible.…”

“…Recently, large interest has been evoked by the investigation of magnetics with more complex anisotropies than one-axis one, whose constants are comparable or even greater than a constant of exchange interaction. In such systems the realization of purely quantum effects is possible [3,4], whose presence can essentially influence the dynamics of the system. The account of ME interaction in such systems can result in a number of interesting effects.…”

“…Thus, there is a problem of construction of the microscopic theory of hound ME waves which enables us to take exactly into account as large OA as ME interaction. It is possible to solve this problem using the Hubbard operators [5,6].…”