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Magnetization curves of ferrimagnetic mixed spin-1 and spin-2 Heisenberg chains are calculated with the help of density-matrix renormalization group method and quantum Monte Carlo simulations by considering a spin dimerization (1,2), trimerization (1,1,2) and tetramerization (1,1,1,2). The investigated mixed-spin Heisenberg chains can be alternatively viewed as a pure spin-1 Heisenberg chain, which contains at a regular lattice positions spin-2 particles. Unlike the antiferromagnetic spin-1 Heisenberg chain solely displaying a zero magnetization plateau due to the Haldane phase, the ferrimagnetic mixed spin-(1,2), spin-(1,1,2) and spin-(1,1,1,2) Heisenberg chains exhibit more striking magnetization curves involving at least two intermediate magnetization plateaux and quantum spin-liquid states. [ABSTRACT FROM AUTHOR]

A method for calculating micromagnetic state of ferro- or ferrimagnetic single-crystals based on the Néel's method of phases is proposed. The standard Néel technique requires different approaches to calculation of micromagnetic state of samples with different anisotropy types. Furthermore, this technique cannot be used to calculate magnetization curves of materials with a complex anisotropy type, in which the first-order magnetization process (FOMP) occurs. On the contrary, the technique proposed in the present work makes it possible to calculate micromagnetic state of a sample within one unified approach. This technique has no limitations in terms of the anisotropy type as well. In case of the FOMP, the simulation methods that we used show results different from conventional calculation methods. The reason is that the conventional methods imply coherent rotation of magnetization in single domain particle (so-called Stoner–Wohlfarth model). We explain this discrepancy by the fact that a magnetic domain structure appears in the region of the FOMP. In the present work we show that magnetization processes do not occur in a jump under the FOMP but gradually pass though nucleation and new high-field phase growing, which substitutes for the low-field phase. [ABSTRACT FROM AUTHOR]

The dimerized ferrimagnetic spin chain has been approached both in the presence and absence of the external magnetic field by using the Villain transformation. Two branches of the low-lying energy modes have been presented and the upper branch of the mode demonstrates the exotic omega-shape when the dimerization parameter is greater than 0.6. We also find that the competition between magnetic field and the dimerization parameter also contribute the omega-shape in lower branch mode. Thermodynamic quantities like free energy, specific heat, magnetization, and susceptibility in finite temperature and magnetic field with different dimerization parameters have also been presented. [ABSTRACT FROM AUTHOR]

Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation function, the thermal and the magnetic properties of a single Ising nanoparticle consisting of a ferromagnetic core, a ferromagnetic surface shell and a ferrimagnetic interface coupling are examined. The effect of the transverse field in the surface shell, the exchange interactions between core/shell and in surface shell on the free energy, thermal magnetization, specific heat and susceptibility are studied. A number of interesting phenomena have been found such as the existence of the compensation phenomenon and the magnetization profiles exhibit P-type, N-type and Q-type behaviors. [ABSTRACT FROM AUTHOR]

Magnetic properties of a trilayer nanostructure of hexagonal lattices described by the spin-1/2 Ising model are investigated via the effective-field theory (EFT) with correlations. In order to clarify the distinction between the ferromagnetic and ferrimagnetic behaviors, the total magnetization, total susceptibility, total inverse susceptibility and critical boundaries have been obtained for positive and negative interlayers couplings. From thermal variations, some magnetic compensation types are found for the ferrimagnetic system. The specificities of the susceptibilities when the magnetizations present compensation temperatures have been also studied. • Correlation identities on a nanostructure of hexagonal lattices are obtained. • From the spin correlation identities the effective-field theory is applied. • The total magnetization and total susceptibility are obtained. • The critical temperature and the compensation temperature are investigated. [ABSTRACT FROM AUTHOR]

In this paper, the magnetic properties of a bi-layer graphyne structure have been studied using Monte Carlo simulations. The considered system is composed of two planes of graphyne with mixed spins: σ = 7/2 and S = 1. Firstly, the ground state phase diagrams for zero temperature are reported and discussed. Secondly, the magnetic properties for the studied system are examined for non-zero temperature. The effects of exchange coupling interaction and temperature on magnetization, susceptibility and transitional temperature. Furthermore, the effects of the crystal field on total magnetization of the system have been exhibited. Finally, the effect of the ferrimagnetic parameter, temperature and crystal field on the hysteresis cycles have been determined. The obtained results have been compared with theoretical and experimental researches. • We study the magnetic properties of a bi-layer graphyne structure. • The ground state phase diagrams are presented and discussed. • The magnetic properties of a bi-layer graphyne structure using Monte Carlo simulations are investigated. • The hysteresis cycles of a bi-layer graphyne structure are analyzed. [ABSTRACT FROM AUTHOR]

By using the method of Dyson–Maleev mean-field theory, we study the effect of bond alternation and longitudinal magnetic field in the model of ferrimagnetic spin chain. Based on the numerical results of self-consistent equations, properties of the excited spectrums, magnon internal energy, static susceptibility, magnetization plateau and specific heat are obtained with different bond alternation parameters δ and external magnetic field B. This method provides qualitative consistent results to describe the phase from ferrimagnetic state to bond altered state. • The transition from ferrimagnetic to dimer state can be described by Dyson-Maleev theory. • The quantum magnetization plateau of mixed spin chain can be tuned by bond alternation parameter. • The result of Dyson-Maleev theory is qualitatively consistent with other numerical method. [ABSTRACT FROM AUTHOR]