Magnetization and magnetostriction of Van Vleck antiferromagnets with magnetic anisotropy of “easy-plane” type

Quantum phase transitions in the anisotropic three dimensional XY model

“…These are the so-called Van Vleck, or singlet, antiferromagnets. These compounds show no magnetic ordering, in the absence of the external magnetic field, at any temperature down to T = 0 [16]. The compound NiCl 2 4SC(NH 2 ) 2 is a prototype of a three dimensional large-D model [17] with D/J ≈ 20.…”

Influence of strong single-ion anisotropy on phase states of 3D and 2D frustrated magnets

“…If the exchange interaction in the basal plane is weaker than the exchange interaction along the axis of the spiral, then the phase transition from the homogeneous phases (quadrupolar and ferromagnetic) into the modulated phase is of the first kind, and Eqs. (16) and (18) determine the stability field of the corresponding phases. The phase diagram of the 3D frustrated magnet is shown in Fig.…”

“…If J 0 o J ð1Þ 0 , then, as it follows from Eqs. (16) and (18), H c2 4H c1 , and only one phase transition of the first kind occurs in the system. This is the phase transition from the ferromagnetic phase into the quadrupolar phase through the co-existence region of the magnetic spiral type.…”

“…In particular, they resemble the properties of antiferromagnets (specifically, the single-axis antiferromagnets in the external magnetic field parallel to the axis of anisotropy). Sometimes such systems are called Van Vleck's paramagnets [12,16].…”

Effect of magnetoelastic interactions on the formation of spiral magnetic structures in frustrated non-Heisenberg magnets

“…These systems are also known as van Vleck paramagnets. 5,9 A biquadratic exchange interaction is another mechanism (besides single-ion anisotropy) that may lead to quadrupole phases. 4,10,11 The existence of higher order exchange interactions in terms of the spin variables can be explained as follows: the Heisenberg exchange hamiltonian is general, in that it is based on an expression made up of atomic spin operators that is invariant with respect to spin rotations.…”