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The magnetic properties of CoAl_2−2xCo_2xO₄ for 0 ≤ x ≤ 1 are studied. The values of the nearest neighbour (J₁), next‐nearest neighbour (J₂), intra‐plane (J_aa) and inter‐plane (J_ab,J_ac) exchange interactions are calculated by the mean field theory for ordered region and by the probability law adapted of the nature of dilution problem in A‐spinel lattice in spin glass region. The high‐temperature series expansions have been applied in the CoAl_2−2xCo_2xO₄ systems, combined with the Padé approximants method, to determine the Néel temperature T_N (K) or freezing temperature T_SG (K) in the range 0 ≤ x ≤ 1. The critical exponents associated with the magnetic susceptibility (y) and the correlation lengths (v) are deduced in the range ordered 0.3 ≤ x ≤ 1. The obtained values of y and v are insensitive to the dilution ratio x and may be compared with other theoretical results based on 3D Heisenberg model.

The purpose of this paper is to synthesize the manganese ferrite nanoparticle MnFe₂O₄ and to investigate the structure, size and to study the electronic and the magnetic properties of MnFe₂O₄ nanoparticles.

The co-precipitation method is used to synthesize the MnFe₂O₄. The structure and size were investigated by X-ray diffraction. The superconducting quantum interference device is used to determine the some magnetic ground. From theoretical investigation point of view self-consistent ab initio calculations, based on density functional theory approach using full potential linear augmented plane wave method, were performed to investigate both electronic and magnetic properties of the MnFe₂O₄. The high temperatures series expansion (HTSE) is used to study the magnetic properties of MnFe₂O₄.

The saturation magnetization, the coercivity and the transition temperature varied between 21-43 emu/g, 20-50 Oe and 571-630 K, respectively, have been studied. The gap energy of MnFe₂O₄ has been deduced. The critical temperature and the critical exponent have been obtained using HTSEs.

In the present work, the authors study the electronic and magnetic properties of MnFe₂O₄. The results obtained by the experiment and by ab initio calculations were used in HTSE as input to deduce other physical parameters.

This paper aims to combine the results of magnetic measurements with high temperature series expansions to determine the magnetic phase diagram of SrMn_1−xFe_xO₃ 0≤x≤1 perovskites materials.

The authors have found antiferromagnetic ordering for lightly and heavily Fe‐substituted material, while intermediate substitution leads to spin‐glass behavior. Near the SrMn_0.5Fe_0.5O₃ composition these two types of ordering are found to coexist and affect one another.

The spin glass behavior may be caused by competing ferromagnetic and antiferromagnetic interactions among Mn⁴⁺ and observed Fe³⁺ and Fe⁵⁺ ions.

The magnetic perovskites materials are several application in industrial applications (spintronics, magnetic random‐access memory (MRAM), …).

The purpose of this paper is to study the magnetic properties of the materials Ni_1−xCo_xMnGe systems by: mean field theory, probability law and high‐temperature series expansions (HTSE) in the range 0≤x≤1. The nearest neighbour J₁(x) and the next‐nearest neighbour super‐exchange interaction J₂(x) are calculated, using the mean field theory and in the range 0≤x≤1.

The magnetic phase diagrams (T_C versus dilution x) and the critical exponents associated with the magnetic susceptibility (γ) and with the correlation lengths (ν) are deduced for Ni_1−xCo_xMnGe in the ordered phase by HTSE method has combined with the Padé approximants method for the Ni_1−xCo_xMnGe.

The obtained magnetic phase diagram of Ni_1−xCo_xMnGe systems is comparable with those obtained by experiment. The values of critical exponents are nearest to those of 3D Heisenberg model and insensitive to the dilution.

Besides the magnetic shape memory effect, the magnetocaloric effect, which exhibits in Ni‐Mn‐Ge or Co‐Mn‐Ge alloys, is of technological interest.

The purpose is to calculate the change in the total energy of a small fragment of an idealized lattice of iron (in its pure form and with impurity atoms) containing an edge dislocation during its elementary motion at one interatomic spacing, both under the influence of a constant magnetic field and without it. The introduction of a magnetic field into the system is aimed at checking the adequacy of the description of the phenomenon of magnetoplasticity by changing the total energy of the atomic system.

The design procedure is based on a quantum-mechanical description of the switching process of the covalent bond of atoms in the dislocation core. The authors used the method of density functional theory in the Kohn-Shem version, implemented in the GAUSSIAN 09 software package. Using the perturbation theory, the authors modeled the impact of an external constant magnetic field on the energy of a system of lattice atoms.

The simulation results confirmed the effect of an external constant magnetic field on the switching energy of the covalent bond of atoms in the dislocation core, and also a change in the magnetic susceptibility of a system of atoms with a dislocation. This complements the description of the magnetoplastic effect during the deformation of metals.

The authors created quantum-mechanical models of the dislocation motion in the Fe crystal lattice: without impurities, with a substitutional atom Cr and with an interstitial atom C. The models take into account the influence of an external constant magnetic field.

The purpose of this paper is to study the magnetic properties and the hysteresis behavior of a ferrimagnetic cubic Ising nanowire with mixed spins S = 3/2 and S = 5/2 in which the atoms are placed alternately.

In order to investigate the effects of the exchange interactions and crystal field on the magnetic properties and hysteresis behavior of the nanowire, we have used the Monte Carlo simulation. More precisely, we have plotted the thermal variations of the sublattice and total magnetizations for different values of the Hamiltonian parameters, and we have presented the corresponding phase diagrams. In addition, the influence of an external magnetic field is examined by plotting the variations of hysteresis loops with the change of temperature and crystal field.

All phase transition found in this study are of second-order and the critical temperatures increase linearly with the increase of the exchange interactions. The compensation temperatures appear only for some domains of crystal field D and exchange interaction J_B of the sublattice (B). Moreover, when studying the hysteresis behavior, the system can show one or double hysteresis loops.

The authors consider that this research is consistent with the scientific axis of the journal which benefits a great esteem in our country and in the world. In addition, the results are of technological interest.

The purpose of this article is to investigate the magnetic properties and the hysteresis loops behavior of a ferrimagnetic cubic nanowire with mixed spins S_A = 3/2 and S_B = 2.

We have used the Monte Carlo simulation to examine the influences of the exchange interaction J_B, the crystal field ∆ and the temperature on the magnetic properties and hysteresis loops of the nanowire. More exactly, we have shown the temperature dependence of the sublattice magnetizations (m_A and m_B) and the total magnetization (M) for several values of the Hamiltonian parameters, as well as the corresponding phase diagrams. Finally, the effect of an external magnetic field is studied by plotting the hysteresis loops of the system for different values of exchange interaction, crystal field and temperature.

The obtained results show the existence of second-order phase transitions, as well as the compensation behavior. Moreover, according to the values of the Hamiltonian parameters, the system can exhibit one, two or three hysteresis loops.

The magnetic nanowires are of great interest in experimental works, but without theoretical explanations, the experimental results cannot be clarified in depth. For this, we contribute through this theoretical study to understand the nanowires, especially those with mixed spins (2, 3/2).