Journal of Superconductivity and Novel Magnetism最新文献

We investigated the magnetic, thermodynamic, and transport properties of polycrystalline GdNiSi₃. The compound crystallized in an orthorhombic structure with the space group Cmmm. Heat capacity and magnetic measurements revealed bulk antiferromagnetic ordering at T_N = 22.5 K, θ_p = -25 K, and an effective magnetic moment of μ_eff = 8 μ_B/Gd. A metamagnetic transition occurred around 28 kOe in the magnetic isotherm at 3 K. Furthermore, resistivity measurements conducted under a magnetic field at 2 K displayed a low-temperature drop near 22.5 K, corresponding to the antiferromagnetic order.

In this study, we examine the effects of pinning forces and pinning center radius on critical current density using a square pinning array and the application of dual conformal transformations. This transformation slightly distorts the square pinning array. We study vortex dynamics by considering the interaction between vortices and pinning centers, as well as the impact of thermal fluctuations. Initially, by determining the mentioned forces that affect vortex dynamics, the corresponding Langevin equation for the vortices is solved. By solving this equation, the position of the vortices over time is determined, and using these positions along with boundary conditions, the critical current density as a function of the magnetic field is calculated. Our studies show that the critical current density increases with the enhancement of pinning force and pinning center radius under conformal transformation.

In this contribution, we present an ab initio investigation of the electronic and magnetic properties of some RhCo-based quaternary Heusler alloys (QH). QH compounds can be generated from doping the X₂YZ full Heusler alloys; in this case, we start our study by tracking the electronic and magnetic properties variation of cobalt-doped Rh₂MnSn. Our results reveal that Co-substitution at Rh sites of Rh_2−xCo_xMnSn (x = 0 to 2) transforms it into half-metallic material when x ≥ 1. The calculated magnetic moment is 4.68µ_B for Rh₂MnSn (x = 0), this value will increase with Co doping to be an integer 5 µ_B when x ≥ 1 obeys the Slater Pauling behavior. The spin polarization at the Fermi level varied from 20.76 to 100%. The Curie temperature (Tc) and exchange interaction are largely dependent on the valence electron number (Nv); for this purpose, we also identify some other quaternary RhCoMnZ (Z = Al, Si, Ga, Ge, Sn, Sb) compounds with different Nv. The exchange parameters (j_ij) and Tc are calculated using the LMTO method. The Tc is calculated with the mean-field approximation (MFA), and the results indicate that all compounds investigated have Tc evidently higher than room temperature making them promising candidates for spintronics applications. The latter results are in better agreement with available experimental and theoretical data.

In this report, soft magnetic properties of amorphous and nanocrystalline (Fe_1−xNi_x)₈₈Zr₇B₄Cu₁ alloys with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 1.0 have been studied. The rapidly solidified ribbons have been prepared using a vacuum melt spinning technique followed by annealing for obtaining nanocrystalline phases. The Curie temperature (T_c) of amorphous phase increases with Ni content upto x = 0.6 and decreases beyond x = 0.6. The saturation magnetisation of as-spun and high-temperature (620/720 °C) annealed ribbons of (Fe_1−xNi_x)₈₈Zr₇B₄Cu₁ alloy system shows a dip at around x = 0.35 which is termed as Invar behaviour. However, Invar behaviour is not observed in 450/500 °C annealed ribbons due to the absence of fcc phase which becomes non-magnetic around x = 0.35 and is responsible for the dip in magnetisation. The coercivity of 620/750 °C annealed ribbons is high as compared to as-spun and 450/500 °C annealed ribbons due to the presence of Fe₃Zr/Ni₅Zr phases.

Nowadays, the concept of non-trivial topological protection and the nanoscale size of nanomagnetic particles constitute a major area of research. Due to topological protection stability, nanoscale size, and the requirement of low spin current density for motion, skyrmions have attracted great attention in next-generation spintronic devices as robust information carriers. We study the motion of an isolated magnetic skyrmion with induced interfacial Dzyaloshinskii-Moriya interaction (iDMI) instigated by a spin wave and driven by spin current with variation in different parameters in a nanotrack of finite length using micromagnetic simulations. It is found that the magnetic skyrmion moves in the same direction as the direction of propagation of the spin wave. The skyrmion initially experiences an acceleration in its motion; thereafter, the velocity decreases exponentially. The motion of the magnetic skyrmion initiates as the momentum of the spin wave gets transferred to it. The motion of the magnetic skyrmion is found to be significantly dependent on the variation of parameters like frequency and amplitude of the incident spin waves, as well as the damping parameter and the strength of the applied spin-polarized current. The results obtained in this work could become useful to design skyrmion-based spintronic information-carrying and storage devices.

Mechanical alloying and hot sintering were used to synthesize Co(_{2})Si-doped powder materials with varying boron (B) and carbon (C) ratios. The effect of B and C doping on the magnetic behavior, microwave absorption characteristics, and crystal structure of the materials was systematically investigated. All X-ray diffraction peaks corresponded to the standard card for Co(_{2})Si (ICDD: 98-005-2281). The saturation magnetization (Ms) values for samples doped with 2, 4, and 8 at% B were 14.28, 19.56, and 7.36 emu/g, respectively. The Ms values for the Co(_{2})Si samples doped with 2, 4, and 8 at% C were 16.66, 19.97, and 14.56 emu/g, respectively. Co(_{2})Si alloys with C significantly improved their overall absorption performance. The minimum reflection loss in the C-doped Co(_{2})Si alloy was (-)61.88 dB, accompanied by a bandwidth of 2.38 GHz for effective absorption. Furthermore, the Co(_{2-x})C(_{x})Si samples (where x = 0.04, 0.08, 0.16) exhibited superior comprehensive absorption properties compared to the Co(_{2-x})B(_{x})Si samples.

Graphene, a two-dimensional material with remarkable electronic properties, offers significant potential for valley-based electronic devices. In this study, we explore a novel mechanism to achieve valley-dependent, near-perfect crossed Andreev reflection (CAR) in graphene-based junctions by utilizing the valley degree of freedom in a graphene/superconductor/line defect superlattice (LDGSL) structure. The LDGSL introduces unique valley-filtering effects. By incorporating staggered pseudospin potentials and intrinsic spin-orbit coupling in the left graphene electrode, the system selectively enhances CAR for electrons in the K(') valley, while simultaneously suppressing local Andreev reflection and elastic cotunneling (ECT). Numerical simulations reveal that CAR is nearly perfect for K(') valley electrons with spin-up, while for K valley electrons with spin-down, only ECT is observed. Our results demonstrate the viability of this approach for valley-polarized CAR in graphene/ superconductor junctions, providing a pathway for the development of valley-based quantum information devices.

The phenomenon of shape anisotropy predominantly constitutes the principal factor influencing effective anisotropy, serving as a significant determinant of the magnetic characteristics of one-dimensional ferromagnetic nanostructures, materials that hold substantial promise for a diverse array of applications in the domains of electronics and biomedicine. However, it is noteworthy that effective anisotropy may be modulated through the manipulation of various other forms of anisotropy, thereby facilitating the tuning of the magnetic properties of nanowire arrays without necessitating alterations to their spatial curvature. In this study, we elucidate the characteristics of nanowire arrays with varying lengths and compositions, which have been electrochemically synthesized utilizing identical porous templates. Through a range of experimental methodologies, we establish a correlation between atypical magnetic behavior and the underlying morphology and crystalline structure of the nanowires. We attribute the pronounced magnetostatic interactions observed within cobalt (Co) nanowires to the presence of significant local uniaxial magnetocrystalline anisotropy, along with a nanostructure oriented perpendicular to the longitudinal axis of the nanowire. Furthermore, we examine the repercussions of substantial discrepancies in the lengths of iron (Fe) nanowires on the magnetostatic field distribution. Our analysis employs mean field theory, incorporating the contributions of various anisotropies present within the system, as well as the non-uniform lengths of the nanowires. Ultimately, through micromagnetic simulations, we investigated the stray fields present within the nanowire array and delineated how strong magnetocrystalline anisotropy and the variability in length affect their spatial distribution.

In the present work, we report the effects of incorporating magnetic Nickel oxide (NiO) nanoparticles in YBa₂Cu₃O_7-x (YBCO), on the superconducting properties of the YBCO nanocomposite. The NiO was prepared by auto-combustion method and exhibited ferromagnetic nature at room temperature. The polycrystalline YBCO and its nanocomposites with NiO nanoparticles were synthesized using the solid-state reaction method. The addition of magnetic NiO nanoparticles in YBCO resulted in improved critical current density and flux pinning force in the measured range of temperature and magnetic fields. The observed high pinning at a lower field is attributed to the magnetic interaction of vortices with the NiO nanoparticles. At 60 K, the enhancement in critical current density of YBCO nanocomposite is ~ 1.7 times for low applied field, and ~ 1.2 times for high applied field, compared to the YBCO superconductor. The presence of NiO in the YBCO matrix also created more defects in YBCO, which enhanced the pinning properties and remained effective even at higher magnetic fields.

Nanomaterials show strong potential for antibacterial treatments by targeting various bacterial strains and bypassing resistance through mechanical cell damage. This occurs when nanoparticles interact with bacterial cell walls, compromising their structural integrity. These mechanisms highlight nanomaterials as effective tools in combating infections. Using the sol–gel method, this study synthesized Co_1-xAl_xFe₂O₄ nanoferrites (x = 0.0, 0.2, 0.4, 0.6, 0.8). This study examines the effects of substituting trivalent Al³⁺ ions on cobalt ferrite nanoparticles’ structural and electrical properties and their antibacterial activity. X-ray diffraction confirmed the formation of Co_1-xAlₓFe₂O₄ nanoferrites in the (Fdoverline{3 }m) space group, showing a shift towards lower 2θ angles in the (311) plane as Al³⁺ content increased. The crystal size reached 29.04 when (x = 0.0 and 0.4) and decreased to 25.29 when (x = 0.8). Fourier transform infrared spectroscopy identified absorption band characteristic of the cubic spinel structure, while field emission-scanning electron microscopy revealed polyhedral nanoparticles clustered in nanoscale formations. Particle sizes ranged from 37.21 nm at x = 0.4 to 31.11 nm at x = 0.8. A decrease in dielectric properties with increasing frequency was consistent with the Maxwell–Wagner model and Koops’ theory, while AC conductivity increased as charge carrier mobility rose with frequency. Antibacterial tests using the Agar well diffusion method showed that Escherichia coli was the most sensitive strain, followed by Klebsiella spp., with Streptococcus spp. Displaying the highest resistance. Nanoparticles at x = 0.8 demonstrated the most potent antibacterial activity. Overall, the results highlight that cation substitution within the cubic spinel lattice significantly impacts the structural, electrical, and antibacterial properties of cobalt ferrite nanoparticles.

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