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In this work, we studied the magnetic properties of a regularly tetrahedral molecule made of four spin-½, interconnected by exchange. For this purpose, we used the Heisenberg model and performed an exact resolution. In the case of a ferromagnetic coupling among the spins, the system orders itself under a magnetic field without displaying any net spontaneous magnetization. It behaves as a high spin-2 unique magnet. Under antiferromagnetic exchange, some exotic behaviour has been revealed due to the frustration governing the spin edifice. Thus, the magnetization is quantized into plateaus, which are separated by quantum phase transitions. In particular, we have argued the possibility of a quantum spin liquid (QSL) state that can occur at low temperature. This contribution intends mainly to bring single-molecular magnets to the front line of innovative nanoscale applications.

In this paper, we study the magnetization behavior in Co40Fe40B20 nanodisks with Dzyaloshinskii-Moriya interaction, which is induced by a Pt layer. The known giant perpendicular magnetic anisotropy (PMA) in thin films elaborated from this kind of materials improves the topological structures nucleation. Our work consists in investigating the skyrmions apparition and stability in amorphous CoFeB nanodisks. The detected skyrmions are not spontaneously nucleated. Their nucleation is induced by an applied external field. We also study reversal magnetization of CoFeB and we elucidate skyrmions nucleation and annihilation.

An effective field method has been employed to study the magnetic properties of a ferrimagnetic mixed-spin Ising trilayer nanographene structure. The system is formed by alternate layers of two different spins atoms A (spin-1) and B (spin-½) arranged in a particular fashion A–B–A for which the nearest-neighbor spins of each layer are coupled ferromagnetically (JA and JB), whereas the cross atom interaction A-B (interlayer) is antiferromagnetic (JAB). We examined the effects of interlayer (or intra-layer) exchange coupling and single-ion anisotropy on the magnetization curves of the system. We found that the antiferromagnetic inter-layers (JAB

In this paper, a calculation model is proposed to measure magnetocaloric effect (MCE) and relative cooling power (RCP) in composites based on magnetic materials underscoring a giant MCE at room temperature. The two composite materials targeted are Gd-Gd5Si2Ge2 and MnAs- Mn 1 + δ As 0.9 Sb 0.1 due to their high magnetic entropy change ΔSM over 270–300 K and 280–320 K. Our selected composites could give a larger RCP value among existing magnetocaloric materials for magnetic refrigeration in the temperature range of 280–300 K which is desirable for ideal Ericsson-cycle magnetic refrigeration. The excellent magnetocaloric properties of these two magnetic composites make them attractive for active magnetic refrigeration at room temperature.

Nanometric spin structures such as skyrmions are covering a large area of applications related to new technologies. In this paper, we carry out a computational study on magnetic skyrmions behavior in Pt/CoFeB/Ru/CoFeB antiferromagnetic-exchange coupled systems. We aim to explore the possibilities of skyrmions nucleation in such multilayer. We demonstrated that skyrmions could be hosted in such system under specific conditions. We also studied the in-plane and out-of-plane reversal magnetization processes for these magnetic multilayers in order to check the skyrmion behavior under magnetic field loops.

The effective field theory with correlations has been employed to study the hysteresis behavior of a ferromagnetic and ferrimagnetic three-walled mixed-spin Ising nanotube with an inner hexagonal vacancy. The effects of different exchange couplings, single-ion anisotropies, and temperature on the hysteresis loops of the sublattices and the overall system are attentively discussed. Multiple hysteresis loops have been observed in the system under certain physical hamiltonian parameters. It is found that the remanences and the coercivity of the sublattices and the system are strongly affected by the temperature, the exchange couplings, and the anisotropy. A satisfactory agreement can be qualitatively achieved by comparing our results with experiments and theoretical studies. Amazing behaviors are revealed thanks to the geometry, the different spins, and the multiple interactions involved in the system.

In this work, the magnetization states under the spin-transfer switching effect are investigated in a nanopillar device composed of a half-metallic Heusler Co 1.5 F e 1.5 G e alloy with a four-fold in-plane magnetocrystalline anisotropy. A comparative study with a half-metallic Heusler alloy of Co 2 F e A l 0.5 S i 0.5 and a typical material of Fe is realized by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation with the Spin-Transfer Torque (STT) contribution, using micromagnetic simulations. Our ultimate goal is to elucidate the origins of the intermediate state (IS) that occurs during magnetization switching by deeply examining the effects of magnetocrystalline anisotropy and shape anisotropy on the magnetization states through analyzing and comparing various switching processes. Our simulation results showed that the magnetization switching via a single-step under low current densities is possible at certain critical cross-sectional dimensions of the ellipse that are adjusted to increase the demagnetization field against the four-fold in-plane magnetocrystalline anisotropy. As well, we provided in this paper a set of appropriate geometric dimensions which allow the magnetization to reverse via a single-step by overcoming IS with minimal spin-polarized current densities.

The magnetization loops of a hexagonal spin-3/2 Ising nanotube are examined in the framework of the effective field theory with correlations, based on the differential operator technique. We have explored the impacts of distinctive exchange couplings on key physical parameters such as Phase diagram, magnetization, susceptibility, internal energy, and specific heat. Some special phenomena are inspected in terms of thermal effects or crystal-field when the other inherent parameters of the nanotube are adjusted. Furthermore, We have found that the exchange couplings, the temperature, and single-ion anisotropy have a strong impact on the shape and the number of hysteresis loops as well as on the coercive field and magnetization behaviors.

The magnetic behavior of the spin - ½ Ising system, consisting of a squared four-legs Nanotube connected to each other by different exchange couplings, have been studied by mean of the effective field theory (EFT). The Nano-system can be immersed in an applied homogenous magnetic field. In addition to the transversal J⊥ and longitudinal J//interactions, we attentively examine the influence of the diagonal exchange interaction Jd on the main thermodynamic variables such as internal energy, spontaneous magnetization, isothermal magnetization, and initial susceptibility. The results show that critical temperature is enhanced with increasing the diagonal exchange coupling strength, while the isothermal magnetization curves can display jumps and plateaus at special values of the applied field, especially at lower temperatures. Our study proves also that the sign and the strength of each exchange coupling constant play a key role in the global magnetic behavior of this single-wall squared Nanotube spin. In particular, antiferromagnetic diagonal exchange interaction can lead to strong frustration.

Skyrmions are viewed as the basic elements for the future generation of magnetic memories. Their small sizes and good dynamical properties give them the ability to store and transport information easily. In this paper, we used micromagnetic simulation to study the contribution of interlayer exchange coupling and the geometrical confinement on scaling magnetic skyrmions. We started the work by comparing the utility of interlayer exchange coupling to the perpendicular magnetic field in scaling magnetic skyrmions. Then, we investigated the effect of combining the interlayer exchange coupling and geometrical confinement to reduce skyrmions size.

Magnetic skyrmions have attracted a great deal of interest in the last decades. They are widely used for many spintronic applications. In this manuscript, we study by micromagnetic simulation the emergence of a hexagonal Neel-type skyrmion lattice in a square thin film of CeFeB. We specifically examine the formation and annihilation of the skyrmion lattice. Moreover, we show the decrease of the skyrmion sizes with the increase of the magnetic field, while the lattice parameter remains unchanged during this rise.

Entamoeba histolytica virulence has been attributed to several amoebic molecules such as adhesins, amoebapores and cysteine proteinases, but supporting evidence is either partial or indirect. In this work we compared several in vitro and in vivo features of both virulent E. histolytica (vEh) and non-virulent E. histolytica (nvEh) axenic HM-1 IMSS strains, such as complement resistance, proteinase activity, haemolytic, phagocytic and cytotoxic capacities, survival in mice caecum, and susceptibility to O2. The only difference observed was a higher in vitro susceptibility of nvEh to O2. The molecular mechanism of that difference was analyzed in both groups of amoebae after high O2 exposure. vEh O2 resistance correlated with: (i) higher O2 reduction ( O 2 - and H2O2 production); (ii) increased H2O2 resistance and thiol peroxidase activity, and (iii) reversible pyruvate: ferredoxin oxidoreductase (PFOR) inhibition. Despite the high level of carbonylated proteins in nvEh after O2 exposure, membrane oxidation by reactive oxygen species was not observed. These results suggest that the virulent phenotype of E. histolytica is related to the greater ability to reduce O2 and H2O2 as well as PFOR reactivation, whereas nvEh undergoes irreversible PFOR inhibition resulting in metabolic failure and amoebic death.