Displacive magnetic phase transitions upon spin ordering in magnets with strong single-ion anisotropy

Physics of the Solid State - This paper reports on the results of investigations into the magnetic ordering of magnets with integer spins of ions and sufficiently strong easy-plane single-ion...     

Supersolid magnetic phase in the two-dimensional Ising-like antiferromagnet with strong single-ion anisotropy

The Ising model with the frustrated exchange interaction for strongly anisotropic antiferromagnetic ultrathin film is investigated in the mean field approximation at low temperatures. It is shown that a spatially inhomogeneous state can be accomplished in the system at a certain relation of material constants values, along with homogeneous states: ferromagnetic, quadrupolar or supersolid magnetic phases. The phase diagram of the system is built on the basis of stability lines analysis.     

Surface magnetization in semi-infinite ferromagnetic semiconductors with single-ion uniaxial anisotropy

A Green's function technique combined with the transfer-matrix method is used to calculate the surface localized-spin and the conduction-electron magnetization in semi-infinite ferromagnetic semiconductors (FMSs) in the ferromagnetic phase taking into account a single-ion uniaxial anisotropy. The theoretical results were applied to narrow-band as well as to wide-band FMSs.     

Two- and single-ion magnetic anisotropy in the rare-earth metals

The strong magnetic anisotropy of the rare-earth metals (basically due to the large oribtal contributions to the total ionic moments) has normally been attributed to the crystalline field acting on the ions. Within the last few years a number of experiments have revealed that anisotropic two-ion couplings are of comparable importance. A review of the experimental evidence for the presence of anisotropic coupling between the rare-earth ions is given. Such indications are found primarily in the excitation spectra of the metals, but are also implicit in the crystal-field parameters determined in dilute systems.     

Optimization of multiferroic properties in the absence of single-ion magnetic anisotropy

The dependence of the average magnetization per site of perovskite B sublattice has been calculated on the assumption of weak single-ion magnetic anisotropy for a quasy-binary solution of Fe³⁺ and nonmagnetic ions. The technique of application of the obtained results to optimize the magnetoelectric characteristics of solid solutions is qualitatively described.     

Quantum phase transition in the two-dimensional XY model with single-ion anisotropy

In this paper we study the quantum phase transition and low temperature behavior in a square lattice quantum two-dimensional XY model with single-ion anisotropy and spin S=1. Starting with the Villain representation, a Landau-Ginzburg expression is written. The large D phase is studied using the bond operator formalism.     

Effect of a staggered magnetic field on the S=1 Haldane chain with single-ion anisotropy

We analyze the gaps in the excitation spectrum of a Haldane chain with single-ion anisotropy in a staggered field. We show that the gap along the direction of the field increases at a faster rate than the others, while its spectral weight decreases, being transferred to a two-magnon continuum.     

The energy bands of quantized spin waves and the uniaxial anisotropy in a biferromagnetic system

The eigenproblems of quantized spin waves in a (100) ferromagnetic bilayer system have been investigated theoretically using the interface rescaling approach. The energy-band structure of the system has been obtained and the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands are explored thoroughly. It is found that all kinds of eigenmodes of the spin waves in the biferromagnetic system are determined by the bulk exchange coupling constant, the interface exchange coupling constant, the spin of lattice, the number of atomic layers and the uniaxial bulk anisotropy. Especially, we explore the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands of first Brillouin zone and the existence condition of all kinds of the eigenmodes.     

Anisotropic effects on the spin fluctuation thermoelectric power of uniaxial ferromagnetic metals

The Boltzmann transport equation is applied to calculate the thermoelectric power of uniaxial and cubic ferromagnetic metals. We present results about contributions taking into account anisotropy effects in the electron-spin and electron-phonon scattering cross-section.     

Quantum magnets with large single-ion easy-plane anisotropy in magnetic field

We propose a theory describing low-temperature properties of magnets with integer spin and large single-ion easy-plane anisotropy D in magnetic field H directed parallel to the hard axis. Considering the exchange interaction between spins as a perturbation and using the bosonic spin representation proposed in our recent paper [1] we find thermal corrections to the elementary excitation spectrum, magnetization and specific heat in the vicinity of the quantum critical point (QCP) H = H _c1(0) ∼ D in the first nonvanishing orders of the perturbation theory. An expression is found for the boundary of the paramagnetic phase H _c1(T) in the H-T plane. The effective interaction between bosons is derived near the QCP. The proposed theory describes well experimental data obtained in NiCl₂-4SC(NH₂)₂ (DTN).     

Specific features of spin ordering in an Ising antiferromagnet with single-ion easy-plane anisotropy

A thermodynamic analysis of spin ordering in an Ising antiferromagnet with single-ion easy-plane anisotropy is carried out. The solutions of the equations of state are analyzed, and the phase diagram is constructed. It is shown that an increase in the single-ion anisotropy constant as a result of increasing competition between single-ion anisotropy and exchange interaction brings about a crossover from the continuous phase transition to the abrupt phase transition. This is initiated by a change in the ion state populations due to single-ion anisotropy and by the freezing of ionic states with a nonzero spin projection. An increase in the single-ion anisotropy also leads to a crossover of the phase transformation between the paramagnetic and antiferromagnetic states from the order-disorder to order-order type.     

Magnetic phase transition in Heisenberg antiferromagnetic films with easy-axis single-ion anisotropy

The staggered susceptibility of spin-1 and spin-3/2 Heisenberg antiferromagnet with easy-axis single-ion anisotropy on the cubic lattice films consisting of n=2, 3, 4, 5 and 6 interacting square lattice layers is studied by high-temperature series expansions. Sixth order series in J/k_BT have been obtained for free-surface boundary conditions. The dependence of the Néel temperature on film thickness n and easy-axis anisotropy D has been investigated. The shifts of the Néel temperature from the bulk value can be described by a power law n^−λ with a shift exponent λ, where λ is the inverse of the bulk correlation length exponent. The effect of easy-axis single-ion anisotropy on shift exponent of antiferromagnetic films has been studied. A comparison is made with related works. The results obtained are qualitatively consistent with the predictions of finite-size scaling theory.     

Effect of particle size distribution on magnetic behavior of nanoparticles with uniaxial anisotropy

The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity(H_C), remanence(M_R), and blocking temperature(T_B) is simulated for an ensemble of single domain ferromagnetic nanoparticles with uniaxial anisotropy. Our simulations are based on the two-state model for T T_B and the metropolis Monte-Carlo method for T T_B. It is found that the increase in the grain size significantly enhances H_C and T_B. The presence of interparticle exchange interaction in the system suppresses H_C but causes MRto significantly increase.Our results show that the parameters associated with the particle size distribution(D_(d,δ)) such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system.     

Multicritical points in a system with random single-ion anisotropy

A system with two competing anisotropies, one of which is random, is considered. Phase diagram in the molecular field approximation with two bicritical points, and a region of metastability is constructed. The renormalization group analysis of the critical behaviour for such a system is carried out. Instead of one of the bicritical points a tetracritical point described by the decoupled fixed point is found.     

Effect of the susceptibility on the magnetic phase diagrams of a ferrimagnet with magnetic instability

The magnetic phase diagrams of a two-sublattice ferrimagnet with a magnetically unstable subsystem are calculated taking account of the susceptibility. Analytic expressions are obtained for the phase-transition fields and critical values of the parameters of the ferrimagnet. The evolution of the magnetic phase diagrams as the susceptibility of the unstable sublattice increases is analyzed.