Transverse Single-ion Anisotropy Research Articles

Critical behavior of the spin-3/2 Blume-Capel quantum model with two random transverse single-ion anisotropies

Using the approach based on the Bogoliubov inequality for free energy, we have studied the magnetic properties of the spin-3/2 Blume-Capel quantum model in the presence of the random transverse single-ion anisotropy (RTSIA). By analysis of the phase diagrams such as temperature versus single-ion anisotropy (τ × φx), magnetization versus single-ion anisotropy (m × φx), and magnetization versus temperature (m × τ) plans, we have obtained information about how the presence of anisotropy affects the properties of the system. We have shown that the RTSIA is responsible for changing the topology of the phase diagrams, compared to the pure model, leading to the appearance tricritical point (TCP).

Thermodynamic properties of the XY ferrimagnetic spin-(1/2,1) chain with both longitudinal and transverse single-ion anisotropies

We investigate the finite temperature properties of the mixed spin-1/2 and spin-1 ferrimagnetic chain with both longitudinal single-ion anisotropy Dz and transverse single-ion anisotropy Dx. The spin excitation spectrum as well as the thermodynamic quantities are explored by means of the Villian transformation theory. We find two branches of the low-lying energy spectrum are strongly dependent on the model Hamiltonian parameters J1,J2, Dz,Dx. Our results agree well with the exact method results for the mixed spin-1/2 and spin-1 Ising chain. The thermodynamic quantities of XY ferrimagnetic spin-(1/2,1) chain varying with Dz and Dx, such as free energy, internal energy, entropy, specific heat and magnetization are explicitly discussed, respectively. The result shows that the magnetization plateaux exists in XY ferrimagnetic spin chain without anisotropy, which indicates a phase transition may occur in XY ferrimagnetic spin chain.

Random transverse single-ion anisotropy in the spin[formula omitted] Blume–Capel quantum model

We have studied the effects of the random transverse single-ion anisotropy in the phase diagram and in the thermodynamic properties of the spin−1 Blume–Capel quantum model, which has been used the approach the mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. The phase diagrams were obtained in the temperature τ=kBT∕zJ versus single-ion anisotropy δx=Dx∕zJ plane for several values of δy=Dy∕zJ, p and q. The results show that there is a tricritical behavior only in the range of δy given by −0.048≤δy<0.5. This behavior is shown again by the curves of the magnetization m as a function of temperature τ with corresponding values of δy, p and q.

Rigorous studies on boundary effects of a dimerized S=1 Ising chain with single-ion anisotropy

We investigate the influences of the boundary conditions on the ground state properties of a dimerized S=1 Ising chain with single-ion anisotropy, which are solved exactly by means of a mapping to the spin-1/2 Ising chain with the alternating transverse fields and the Jordan–Wigner transformation. We obtain the exact results of the minimal energy gap Δ0 for exciting a fermion quasi-particle, the minimal energy gap Δh for exciting a hole and the ground state phase diagram under various boundary conditions. The results show that the boundary conditions do not change the quantum phase transition points of the system, but the minimal energy gaps in the cases of periodic and open boundary conditions are quantitatively different. When the dimerized transverse single-ion anisotropies parameter D1>D2, the ground state is lied in the non-hole systems with arbitrary lattice sites. But if D1<D2, holes will appear in the ground state of system with odd lattice sites.

Exact results of an alternating-bond mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies

The alternating-bond mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies are solved exactly by means of a mapping of the spin-1/2 transverse Ising chain and the Jordan–Wigner transformation. The ground state quantities are strongly dependent on the model Hamiltonian parameters J 1, J 2, D x and D z . We obtain the quasi-particles' spectra Λ k , the dimerization gap Δ d , the minimal energy Δ 0 for exciting a fermion quasi-particle, the minimal energy gap Δ h for exciting a hole and the ground state energy E g . The phase diagram of the ground state is also given. The results show that the alternating bond just quantitatively changes the ground state properties; no matter the nearest-neighbor exchange interactions J 1 and J 2 are equal or not, when D z ≥0 for any finite value of D x , there is no quantum critical point and the ground state is always in a spin ordered phase.

Thermodynamic properties of the mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies

The mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies is solved exactly by means of a mapping to the spin-1/2 Ising chains with alternating transverse fields and the Jordan–Wigner transformation. Within this scheme, the thermodynamic quantities of this model are rigorously determined by a recursion formula derived for the partition function based on the reduced spin-1/2 transverse Ising model. The corresponding thermodynamic properties are calculated and discussed.

Exact results of a dimerized S=1 Ising chain with single-ion anisotropy

The dimerized spin-1 Ising chain with both longitude and transverse single-ion anisotropies D z and D x is solved exactly by means of a mapping to the spin- 1 2 Ising chain with the alternating transverse fields and the Jordan–Wigner transformation. The analytical expressions of the quasi-particles’ spectra Λ k , the minimal energy gap Δ 0 for exciting a fermion quasi-particle, the minimal energy gap Δ h for exciting a hole, and the ground-state energy E g are obtained. The phase diagram of the ground state is also given. The results show that the system exhibits a series of quantum phase transitions depending on the dimerization strength of the crystal fields, while the quantum critical points are determined exactly.

Exact results of a mixed spin-1/2 and spin-1 Ising chain with both longitude and transverse single-ion anisotropies

The mixed spin-1/2 and spin-1 Ising chain with both longitude and transverse single-ion anisotropies D z and D x is solved exactly by means of a mapping to the spin-1/2 Ising chain with the alternating transverse fields and the Jordan–Wigner transformation. The analytical expressions of the quasi-particles' spectra Λ k , the minimal energy gap Δ 0 for exciting a fermion quasi-particle, the minimal energy gap Δ h for exciting a hole, and the ground state energy are obtained. The phase diagram of the ground state is also given. The results show that when D z ⩾ 0 for any finite value of D x , there is no quantum critical point and the ground state is always in a spin ordered phase disregard of the boundary condition in the present system.

The effect of single-ion anisotropy on the specific heat of a spin-one Heisenberg antiferromagnetic chain in an applied magnetic field

The specific heat of a spin-one Heisenberg antiferromagnetic chain with transverse and longitudinal single-ion anisotropies in the presence of an applied magnetic field is explored on the basis of the Schwinger boson mean-field theory. The specific heat as functions of temperature, the anisotropy as well as the applied field are discussed, respectively. The results indicate that new features of the specific heat as a function of temperature at the transverse single-ion anisotropy are very different from those obtained at longitudinal single-ion anisotropy in an applied transverse field.

Phase transitions in an ising ferromagnet with transverse single-ion anisotropy (spin [formula omitted

Phase transitions in an ising ferromagnet with transverse single-ion anisotropy (spin [formula omitted