Journal of Superconductivity and Novel Magnetism最新文献

The Fullerene C18 is one of the most active types of nanostructures used as an active ingredient in several applications. This study used Monte Carlo simulations to investigate the magnetic properties of mixed 3/2 and 2 in the fullerene C18 systems. We first perform a theoretical analysis of the ground state phase diagrams. Indeed, we only present and analyze more stable configurations among all possible configurations. Second, calculations were performed to determine how the compound's magnetic properties changed when various physical parameters were altered. In addition, we provide studies of the magnetic behavior of the system at reduced temperature, reduced crystal fields, reduced exchange coupling interactions, and reduced external magnetic fields. Finally, we study and discuss the critical lowering temperature of fullerene C18. To conclude this study, we examined the different hysteresis loops when varying the values of the different physical parameters.

We study the energy gap within the Dynes superconductor theory. This model generalizes the Bardeen-Cooper-Schrieffer (BCS) approach by including the pair-breaking scattering, introducing the tunneling in-gap states up to a Fermi level. We analytically solve the energy gap equation in various limit cases. The solution provides simple tools for further studies, compared to more complex numerics, and highlights the basic characteristics of the theory. First, in the critical limit of pair-breaking scattering, we derive an analytical form of zero-temperature gap to transition temperature ratio. Next, we derive the dependence of the energy gap close to critical temperature and look at its behavior for general and critical pair-breaking scattering rate. Furthermore, we compare our result with the numerical solution of the gap equation assuming general temperature. We show the range of temperatures, for which the analytical approximation is valid. In the end, we provide the approximative formula of the gap, assuming general pair-breaking scattering, emphasizing its exact behavior close to transition temperature.

Recent reports of superconductivity in the vicinity of room temperature have been the subject of discussion by the community. Specifically, features in the resistance-temperature (R-T) relations have raised questions. We show that many of these features can arise from previously unaccounted-for dynamic effects associated with the AC transport techniques often used in high-pressure experiments. These dynamic AC effects can cause the apparent resistance (( R_{apparent} )) to diverge from the DC resistance (( R_{DC} )), sharpen measured superconducting transitions, and produce other features in the measured R-T response. We also show that utilizing the full output of phase-sensitive transport measurements provides a valuable probe of superconducting samples in difficult-to-measure systems.

As magnetic refrigerants, first-order transition (FOT) and second-order transition (SOT) materials possess distinct advantages and disadvantages. If the phase transition can be tuned to the critical point between FOT and SOT, it may be possible to combine the benefits of both, thereby achieving an outstanding magnetocaloric effect. Here, we demonstrated this approach through phase transition engineering in Er(Co_1-xMn_x)₂ alloys. When x ≤ 0.06, the magnetic phase transition of the samples was FOT, exhibiting a significant magnetic entropy change. However, at x = 0.08, the samples underwent a SOT from ferromagnetic to paramagnetic, leading to a substantial reduction in the magnetocaloric effect. At the critical point of the FOT/SOT border with x = 0.06, the sample exhibited a large magnetic entropy change along with negligible magnetic hysteresis. This work demonstrates that the critical point between FOT and SOT is an effective means of achieving an excellent magnetocaloric effect.

In pursuing energy-efficient and high-performance nonvolatile magnetic memory devices, this study explores voltage-induced techniques, specifically voltage-controlled magnetic anisotropy (VCMA), as an alternative to current-induced methods, which suffer from Ohmic loss. The perpendicular magnetic anisotropy (PMA) nanomagnet, known for its superior stability and scalability compared to in-plane variants, VCMA switching in PMA system requires an in-plane symmetry breaking field, which limits its practicality for on-chip applications. We investigate field-free VCMA switching utilizing strain from a piezoelectric layer and an exchange bias from an antiferromagnetic material. Using macro-spin simulations based on the Landau-Lifshitz-Gilbert equation, we systematically analyze how the VCMA effect, strain-induced magnetoelastic effect, exchange bias, oxide and free layer thicknesses, and damping constant affect the switching performance of the device. The write error rate (WER) drops drastically from 0.2 (without stress) to ({10}^{-6}) (100 MPa stress), showcasing the effectiveness of our approach. We also find that the damping constant, especially in the 0.01–0.05 range, plays a crucial role in further optimizing the switching performance of the device. This study offers new insights for enhancing magnetic memory technology.

Superfluid phase stiffness (SPS) in the presence of two co-existing and mutually exclusive superconducting and magnetic ordering has been studied in (i) the pure EBCO and (ii) a composite system of nanoparticles of Sn and EBCO superconductors. SPS has been extracted in two different methods by using (i) nonlinear current–voltage (IV) characteristics and (ii) magnetization (M) as a function of the applied magnetic field (H). Variations of the SPS with temperature (T) are found to be different in transport and magnetic methods. A possible reason of the difference has been discussed. The nature of the variation of the SPS in the presence of nanoparticles of Sn has been explored in terms of the distribution of the bound vortex–anti-vortex pairs within the framework of the BKT transition.

This work attempted to study the effects of the solidification behavior on the magnetic and magnetocaloric properties of stoichiometric Ni₅₀Mn₃₄In₁₆ Heusler alloy. In this respect, the samples with two different diameters of 2 mm (D2 sample) and 8 mm (D8 sample) were prepared by suction casting technique. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and magnetic force microscopy (MFM) were employed to identify the structure, microstructure, and magnetic domain distribution of the samples. Also, phase transformation behavior was characterized using differential scanning calorimetry (DSC) across a temperature range of 200–350 K. Thermo-magnetic properties of samples were evaluated using SQUID Quantum Design MPMS®3 during heating and cooling at the temperature range of 175–350 K at the constant magnetic field of 2 T. Moreover, the magnetic and magnetocaloric properties of the samples were analyzed using the cryostat-equipped VSM around the magnetic phase transition temperature under a magnetic field up to 1.75 T. Based on the results obtained, it is shown that an increase in the sample diameter leads to an increase in the Curie temperature. Furthermore, it was concluded that the magnetocaloric properties such as magnetic entropy change ((Delta {S}_{text{M}})), adiabatic temperature change ((Delta {T}_{text{ad}})), and refrigerant capacity ((RC)) parameters improved with an increase in the sample diameter through the microstructural refinement and enhancing the atomic ordering. Specifically, the maximum values of the (Delta {S}_{text{M}}), (RC), and (Delta {T}_{text{ad}}) for the D8 sample are estimated to be 3.04 J/kg K, 109.83 J/kg, and 0.94 K, respectively.

Underwater wireless communication is an exciting and demanding technology, where communication for longer distances with less noise is essential. The widely used underwater communications, such as communication by acoustic waves, and terrestrial waves, such as optical and radiofrequency waves, have limitations. Communication by magnetic induction appears to be an alternative technique, which needs an improvement in long-distance communication. Storing the data digitally and sending the higher current pulses to the transmitter coil will generate stronger magnetic pulses. The digital magnetic pulses can transfer the data to longer distances, increasing the transfer rate.

This paper studies the nano-diamond structure, commonly known as the ultra-dispersed diamond (UDD) structure. This diamond-decorated system is formed with the mixed spins S = 2 and σ = 3/2. This study uses the Monte Carlo simulations (MCS) under the Metropolis algorithm. We envisaged both the first nearest-neighbor interactions and the second nearest-neighbor interactions. For simplicity, we used the reduced crystal and external magnetic field. When fixing the other physical parameters, we inspected the temperature effect on the phase diagrams of the studied system. Also, we illustrated the thermal behavior of the magnetic entropy changes of the studied system for several reduced external magnetic field values. In addition, we presented the relative cooling power (RCP) as a function of the reduced external magnetic field of the (UDD) system. The effect of the reduced crystal field on the magnetizations of the diamond-decorated system has been investigated. To complete this study, we presented and discussed the magnetic hysteresis cycle of the studied diamond-decorated system.

Tetra metal nitrides (M₄N; M = Cr, Fe, Co, Mn, Ni) are a promising spintronic material with an anti-perovskite structure and fascinating magnetic characteristics due to a magneto-volume effect. Though a fully stochiometric Mn₄N or Fe₄N has been achieved, the lattice parameter (LP) of Co₄N was always been found to be significantly lower than the anticipated theoretical values, indicating a sub-stochiometric Co₄N phase. The formation enthalpy of Co₄N is slightly positive resulting in unfavorable thermodynamical conditions and significant out-diffusion of N from Co₄N. In this work, we present a comparative study of undoped and Pd-doped Co₄N thin films synthesized using a reactive nitrogen sputtering. The structural, composition, and magnetic properties have been studied by combining x-ray diffraction, Rutherford backscattering, energy-dispersive x-ray spectroscopy, secondary ion mass spectroscopy, vibrating sample magnetometer, magneto-optical Kerr effect, and polarized neutron reflectivity measurements. It was found that Pd doping of about 5 at.% results in a significant enhancement in the LP of Co₄N signifying a higher amount of N retention without adversely affecting the growth and magnetic properties. It is further suggested that the amount of Pd doping may further be increased to realize a fully stoichiometric Co₄N.