Journal of Superconductivity and Novel Magnetism最新文献

In this contribution, we studied the magnetization, magnetic susceptibility, and electronic superconducting density of a superconducting irregular octagon in the presence of an external magnetic field H. We solved the time-dependent Ginzburg-Landau equations (TDGL) for a one-band condensate for a mesoscopic type-I sample ((kappa <1/sqrt{2})). Our results show the existence of Shubnikov-vortices in the up-branch of the magnetic field (H). Also, we found a paramagnetic response in descending field. We think that the vortex state proposed here reflect intrinsic features of the superconducting sample.

Here, equal numbers of La and Mn ions are successfully introduced simultaneously in SrRuO3. With increasing La/Mn doping, all compositions crystallize in Pnma with the lattice constant, together with the RuO₆ octahedral distortion, decreases. Ferromagnetism-to-spin glass magnetic behavior is observed at x ≥ 0.23. A metal–insulator transition (MIT) occurs at lower temperatures, resulting from the disordering of the metal mixture in the lattice. The retraction of the RuO₆ octahedron increases the overlap of the Ru t_2g–O 2p orbitals and broadens the Ru 4d bandwidth, leading to weaker electron–electron interactions, which may decrease the electronic and thermal conductivity.

Perovskite type nanocrystals of La_2 − xIn_xCuO₄ were prepared by using the combustion method. The magnetic, optical, morphology, structural, and vibrational characteristics were investigated using techniques like XRD, FE-SEM, FTIR, VSM, EDX, and DRS-UV. The development of the pure La₂CuO₄ perovskite structure was established by XRD analysis. When there is an increase in the indium ion concentration (x = 0.00 to 0.25), orthorhombic phase takes place. The orthorhombic structure crystallite size is from 54 to 38 nm, respectively. The oxidation states of the synthesized nanoparticles were carried out via X-ray photoelectron spectroscopy (XPS). TG-DTA studies confirmed weight loss and exothermic transitions. Because of quantum confinement phenomena, the direct band gap energy increases with an increase in In³⁺ ion content (1.70 to 1.73 eV) and that was calculated using the Kubelka–Munk method. The La₂CuO₄ system demonstrates the formation of nanoscale crystalline grains with fused grain boundaries, resulting in the presence of pores and pore walls. The magnetization-field method yields hysteresis curves at room temperature (RT) that indicate the existence of ferro/paramagnetic characteristics.

This work describes the use of urea as fuel and a simple solution-based approach technique for both the pure and Ce-doped ZnMn₂O₄. The magnetic, structural, optical, morphological, vibrational spectroscopy and solar cell analysis were performed on the resultant materials. By increasing the Ce doping, the grain size shrank. On the other hand, the average crystallite size of pure and Ce-doped ZnMn₂O₄ represents 29–21 nm. The results of vibrational spectroscopy revealed that the absorption bands 450–900 cm⁻¹ and 950–1050 cm⁻¹ both exhibit spinal manganite formation. The morphologies of the highly uniformly distributed nanoparticles in each sample varied according to the preparation. To reach the Ce doping level, the band gap energy (1.4–2.2 eV) was lowered from the bulk to the nanoscale. M-H loops, the composites showed that cations were paramagnetic to ferromagnetic, were occupied by octahedral and tetrahedral structures. Additionally, the impact of doping on the optical and structural characteristics of various blends was investigated. This advancement suggests the application of prepared blends in various optoelectronic, electrochemical, storage devices, and solar cell applications.

This study aims to examine the effects of milling time on the morphological, structural, and magnetic properties of nanostructured Ni₅₀Ti₅₀ powders prepared by high-energy mechanical alloying using a Fritsch Pulverisette 7 planetary ball mill. Scanning electron microscopy and electron dispersive X-ray spectroscopy, results revealed a novel particle folding phenomenon during high-energy milling, significantly diverging from conventional welding and fracture processes. With increasing milling time, it was observed reduced particle size, and enhanced spherical equiaxial morphology, alongside a mixture of the amorphous phase, NiTi-martensite (Ms), NiTi-austenite (As), and solid solution phases (SS). Rietveld refinements of X-ray diffraction patterns and magnetic measurements highlighted the critical role of the amorphous phase in determining the Ms and Mr values of synthesized Ni₅₀Ti₅₀ powders. After 72 h of milling, the coercive field increased to 285.8 Oe, and the martensitic phase proportion reached 21.58%.

An upsurge of research activities is conducted to assess the magnetic properties of graphene nanoribbons with a keen focus on spintronic applications. The critical and compensation characteristics of mixed spin-3/2 and spin-1/2 Ising nanoribbons (Nrbs) with rectangular and hexagonal shapes under a transverse field are explored employing the finite cluster approximation. In the absence of transverse fields, only the rectangular Nrb, may exhibit one or two compensation points. This compensation persists under a transverse field Ω_σ that exclusively affects the spin-1/2 of the σ-sublattice, where the order is destroyed at some J_σ-dependent critical transverse fields at T = 0. Interestingly, the insertion of a transverse field Ω_S acting only on the S-sublattice, demonstrates that the order cannot be destroyed at low temperatures, with the possibility of reentrance as well as tricritical behaviors for rectangular Nrb. Finally, all these behaviors have been confirmed through an analysis of the magnetizations.

In view of tuning different transitions, Co and V are substituted in Mn-rich Ni-Mn-Ga alloy. Ni₄₁Co₉Mn₃₀V₂Ga₁₈ sample undergoes a coupled magnetostructural transition above room temperature with a low thermal and magnetic hysteresis and high sensitivity of martensite transition temperature (8 K/T) with the field. ∆S_M is found to be a maximum of −2.33 J/kg-K for 3 T field change with a large RCP of 158 J/kg. The presence of intermartensite transition along with the magnetostructural transition widens the range of working temperature.

Excellent soft magnetic properties of the amorphous and nanocrystalline alloys are attributed to their unique microstructure. In this work, Fe_73.5Si_13.5-xNb₃Cu₁B₉P_x (x = 0, 3.5, 7, 10 at. %) amorphous ribbons have been fabricated using the melt spinning technique. The effect of annealing temperature (475 ~ 600 ℃) on the microstructure and soft magnetic properties have been studied. According to the results, the thermal stability of FeSiNbCuBP amorphous alloys was improved by the partial substitution of Si by P. Moreover, it was found that the grain growth of α-Fe (Si) phase can be restrained by the appropriate amount of P addition and result to a grain refinement of the alloys during annealing. Base on refinement grain size (9 nm) and optimal crystallization volume fraction (47%), Fe_73.5Si₁₀Nb₃Cu₁B₉P_3.5 nanocrystalline alloy with low coercivity of 0.02 A/m and high effective permeability of 3.22 × 10⁴ was developed after annealed at 525 ℃. Besides, we propose that the migration of free electrons from P to Fe could diminish the saturation magnetization of these alloys.

The realization of an effective p-type doping in Ga₂O₃ is crucial for both fundamental science and emerging applications. P-type doping in the β-Ga₂O₃ phase has been observed tremendously, whereas the researches of p-type features in the allotropy α-Ga₂O₃ phase are rare. In this work, we study p-type N-doped α-Ga₂O₃ by first-principles calculations with generalized gradient approximation (GGA) + U method. The N foreigner can easily substitute the O atom in α-Ga₂O₃ and acts as an effective shallow hole dopant with a modest acceptor ionization level of ~ 0.1 eV. Moreover, the N³⁻, N²⁺, and N³⁻ are the predominant charge states, corresponding to one N impurity substitution of anion O, cation Ga, and the occupancy of the interstitial site in α-Ga₂O₃, respectively. N impurity leads to the optical transition from ultraviolet light to visible-infrared range in α-Ga₂O₃ as suggested by the dielectric function calculations, which can be ascribed to the transition from O 2p orbitals to N 2p orbitals or inter-band transition between the formed holes of N 2p impurity. Our work may provide theoretical guidance for designing p-type N-doped α-Ga₂O₃ materials and shed light on its application as potential optoelectronic devices.

We present our findings on the room temperature (RT) soft ferromagnetism (FM) of the sol-gel-prepared Co-doped barium titanate (BaTiO₃) nanoparticles with two distinct Co concentrations (0.25 mol% and 0.5 mol%), that is appropriate for spintronic applications as evidenced by experimental observations. X-ray diffraction investigation revealed that the produced samples, which had diameters less than 100 nm, belonged to the pseudo-cubic phase of the BaTiO₃ structure and did not exhibit any signs of the Co cluster or any other Co oxides. UV-visible absorption spectra demonstrate that the optical response is red shifted and the bandgap energy is lowered when Co is incorporated into the BaTiO₃ lattice. The inclusion of cobalt ions may have brought about a change in size or an increase in surface defects, as evidenced by the PL spectra, which show that the intensity of emission peaks changes as the dopant concentration increases. In the 0.25 mol% Co-doped BaTiO₃ sample, the FM behavior is clearly visible along with the paramagnetic (PM) phase at RT. Significantly, it becomes apparent that as the doping concentration is raised to 0.5 mol%, the saturation magnetization is reduced, and a pure phase of soft FM is obtained. This soft FM feature witnessed in 0.5 mol% doped BaTiO₃ with low coercivity (96.8 Oe) and low saturation magnetization (9.7 × 10⁻³ emu/g) is likely due to oxygen vacancies and could set out as a promising magnetic material for possible spintronic applications.