SPIN

This work explores the frequency comb of magnetic vortex in a square disk and a circular disk created by an out-of-plane and in-plane oscillating field using micromagnetic modeling. The broadest frequency comb ever observed in a magnetic system is displayed. When driven by an out-of-plane field, the robustness of the frequency comb of a vortex in a square disk is significantly enhanced due to a reduction in rotational symmetry when compared to a vortex in a circular disk. In addition, comb lines increase as driven amplitude increases, and frequency spacing could be adjusted in the square disk, so facilitating its application. In a situation where the vortex is driven by in-plane field, the square disk exhibits a significantly neater frequency comb than the circular disk. The conclusion is that magnetic vortex in a square disk is better suited for frequency comb applications.

In this study, the mean-field approximation (MFA) is applied to the study of the XZ model for spin-1/2 in terms of Pauli spin matrices and their exponentials to obtain the magnetization components for the ferromagnetic (FM) and antiferromagnetic (AFM) cases. The details of obtaining the series expansion for the exponential Pauli spin matrices by using their fundamental properties and commutativity relations are presented. The partition function, free energy, and magnetization are obtained for a given coordination number in a simple form as hyperbolic tangent functions. The thermal variations of the magnetization components in the x- and z-directions are studied to obtain the phase diagrams in possible planes, which only present the second-order phase transitions. The reentrant behavior is also observed in the AFM case.

In this paper, we studied the magnetic stability, structural, elastic and electronic properties of Ir₂FeAl full Heusler compound in the regular phase (Cu₂MnAl, prototype L2${}_1)$, by using the first principle of density functional theory, with the generalized approximation of the GGA gradient. We found that the ferromagnetic state of Ir₂FeAl is more stable than the nonmagnetic configuration at their lattice parameters equilibrium. This result was confirmed by the calculation of the cohesive energy. The stability is asserted by the elastic constants and the conditions of the mechanical stability criterion. The band structure and the calculated densities of states (DOS) of this alloy show a semi-metallic behavior. The ferromagnetic performance of Ir₂FeAl is confirmed by the total magnetic moment of 4.28 ${\mu }_B$, where its major contribution comes from Fe atoms. We estimated the Debye temperature of Ir₂FeAl from the average speed of sound. This is the first quantitative theoretical prediction of the elastic properties of the Ir₂FeAl compound, and it still awaits experimental confirmation.

The manipulation and detection of antiferromagnetic (AFM) in exchange bias (EB)-based MRAM using spin-orbit torque (SOT) holds promise for developing highly reliable and ultrafast spintronic memory devices. However, the high switching current induced by the SOT-induced EB field remains a major drawback. Additionally, the mechanism behind the interaction between the EB field and the SOT remains unclear. To address this issue, we have introduced a thin layer of Mo between the AFM and ferromagnetic-free layers to tune the EB field and study the SOT-induced switching properties. Our findings indicate that when the SOT is dominant during short pulses of a few nanoseconds, Mo insertion can significantly reduce the EB field and decrease the SOT switching current, leading to a reduction in power consumption of these memories. This approach could open up new possibilities for optimizing EB-MRAM and improving our understanding of AFM electronics.

We studied the phase transitions of the $J_1-J_2$ spin-1/2 Ising model in the square lattice by considering $J_1$ fixed and $J_2$ as random interactions following discrete and continuous probability distribution functions. The configuration of $J_2$ in the lattice evolves in time through a competing kinetics using the Metropolis algorithm leading to a steady state without reaching the free-energy minimum. So, different phase diagrams were obtained according to the distribution of $J_2$. For fixed and random values of $J_2$, we noted that the amplitude of the correlation length is different from the Ising value at the critical point of the superantiferromagnetic–paramagnetic frontier.

The mixed spin Ising nanowire with random and dilute crystal fields has been explored based on the finite cluster approximation. Much concern has been addressed in treating the effects of the randomness with two distribution types of the crystal field on the phase diagrams. It has been demonstrated that for a low random crystal field D marked by the fluctuation d, all transition lines are of second order and are not particularly sensitive to the fluctuation; whereas, for high values of D, the transition temperature depends on the fluctuation and may display tricritical points. Under the effect of the dilute crystal field, according to the surface shell coupling strength, the tricritical behavior occurs exclusively for higher values of the concentration p where a large majority of spins are influenced by the crystal field. All these behaviors have been confirmed by examination of magnetizations.

In this work, we study the ground state phase diagrams and the magnetic properties of the mixed spins ($S=3∕2$, $G=5∕2$) of the silicene–germanene junction-like nanostructure. In the first step, the ground state phase diagrams have been established to show the more stable configurations corresponding in different physical parameter planes. Besides, we have used the Monte Carlo simulations in order to study the magnetization and the susceptibility as a function of the temperature and the exchange coupling interaction and external magnetic field effects. Finally, we have presented and discussed the hysteresis cycles for specific values of the studied physical parameters.

This work aims to investigate the thermodynamic properties and magnetocaloric effect (MCE) of spins - 1/2 square lattice using Monte Carlo simulation. The considered Ising model is parameterized by the couplings J, $aJ$ and $bJ$; where J is the ferromagnetic exchange interaction between first nearest-neighbor spins, a is the anisotropic parameter and $bJ$ is the ferromagnetic exchange interaction between second nearest-neighbor spins. Monte Carlo simulation under Metropolis algorithm allows us to study some thermodynamic properties and MCE of spins - 1/2 square lattice. The discussion of the obtained results allowed us to specify the conditions which can enrich the MCE in spins - 1/2 square lattice. The two-dimensional anisotropic Ising model presents clarifying the critical point of the ferromagnetic–paramagnetic transition, and we have shown that the maximum entropy variation increases when it occurs at the ferromagnetic–paramagnetic transition temperature regardless of the intensity of the applied magnetic field and the values of “a” and “b”.

A monolayer anthracene-like nanostructure was investigated through Monte Carlo simulations to determine its compensation temperature and magnetic hysteresis cycle. Also, the effects of exchange coupling on compensation and transition temperatures were discussed. Additionally, the magnetic hysteresis cycles and magnetic coercive field as well as the surface of multi-loop hysteresis were studied with respect to strong exchange coupling and temperature parameters. This study discusses the behavior of multi-loop hysteresis in multi-state memories and nanotechnology.

Magnetic random-access memory (MRAM) is one of the most promising next-generation purpose memory devices for nonvolatile storage and in-memory computing. However, material defects can affect the performance of the MRAM device. Here, the relationship between the material defects and the properties of CoFeB–MgO-based MRAM have been studied with micromagnetic simulations. The results show that the coercivity and the switching speed are strongly influenced by the material defects. This work provides a useful guideline for the fabrication of the MARM devices.