Journal of Superconductivity and Novel Magnetism最新文献

Magnetic measurements in different thermal-magnetic cycles were carried out on a SmBa₂Cu₃O_7-y single crystal with high critical current density. Two magnetization peaks were simultaneously observed on this strongly pinned sample in different thermal cycles. It was observed that a large and broad maximum on magnetization curves manifested only on a single magnetic field dependent magnetization M-H curve but not on a single zero-field cooling temperature dependent magnetization M-T curve, which was usually defined as fishtail effect (FE). The FE was an irreversible property mainly originated from strong pinning centers. On the other hand, the much smaller magnetization peak manifested only on field cooling M-T curves, which was reversible peak effect (PE). The PE took place at higher temperatures near vortex solid–liquid transition and may be caused by dense and weak pinning centers.

In this study, MgB₂ bulk superconductors doped with 0–20% wt SiC were synthesized via in‑situ Spark Plasma Sintering (SPS), and their physical and magnetic properties were systematically investigated. Resistivity–temperature (ρ–T) and H–T phase diagram analyses revealed that while increasing SiC content reduces the transition temperature (T_c) and broadens the transition width (ΔT_c), it simultaneously enhances flux pinning and magnetic stability through a dual mechanism. Specifically, partial decomposition of SiC at 850 °C leads to carbon substitution in the MgB₂ lattice, increasing electron scattering and creating effective lattice distortions, while residual SiC nanoparticles and Mg₂Si secondary phases act as volumetric and intergranular pinning centers. Critical current density (J_c) and normalized pinning force (F_p/F_p,max) analyses confirmed strong pinning performance, particularly at 10–15% wt doping levels, where both J_c and H_irr were maximized. Vertical and lateral levitation force measurements under zero‑field‑cooled (ZFC) and field‑cooled (FC) conditions further demonstrated that the 15% wt sample exhibited the most stable flux trapping capacity, maintaining strong magnetic response even near the superconducting transition. Notably, the sample with 5% wt SiC addition exhibited the highest critical current density of 1.08 × 10⁶ A/cm² at 20 K under self-field, confirming the effectiveness of optimized doping for high-performance applications.These results confirm that controlled SiC doping and SPS processing effectively tailor MgB₂ bulk superconductors for high‑performance magnetic and levitation applications.

In 1991, V. J. Emery in his important review article entitled “Some aspects of the theory of high temperature superconductors” (Emery, Phys. B: Condens. Matter. 169, 17–25 1991) argued against the Zhang-Rice reduction of three-band to an effective one-band model. In his words “...therefore it seems that the simple (t-J) model does not account for the properties of high temperature superconductors”. Over approximately 35 years after the initial debates much has happened in the field pertaining to this topic. Even though it is one of the most discussed issue, a comprehensive account and the required resolution are lacking. Connected to the debate over one-band versus three-band models is another discussion: the one-component versus two-component model for cuprates. The two-component model is most strongly advocated by Barzykin and Pines (Adv. Phys. 58, 1–65 2009). In this article the author attempts a perspective and a re-look on some of these issues. After an analysis of a large body of literature, author finds that V. J. Emery’s criticism of the Zhang-Rice reduction was correct. Many central experimental features of cuprates cannot be rationalized within the one-band model, and Johnston-Nakano scaling is one such example. Other examples are also discussed. Author introduces a simple-minded toy model to illustrate the core issues involved.

This study investigates the structural, optical, and magnetic properties of double perovskites (DP) structured Ba₂FeMnO₆ (BFMO) synthesized via the solid-state reaction method. Rietveld refinement of X-ray diffraction data confirms the formation of a cubic structure with space group Fm-3 m (#225) and high phase purity. Fourier Transform Infrared (FTIR) spectroscopy verifies the presence of metal–oxygen bonding. UV–Vis spectroscopy and Tauc plot analysis determine an optical band gap of 2.1 ± 0.01 eV. Magnetic measurements reveal room-temperature weak ferromagnetic (FM) behavior. These findings highlight BFMO's potential for room temperature spintronic applications.

Development of wide band gap semiconductor with ferromagnetic properties over a wide temperature range is a long standing demand for their applications in multifunctional spintronic devices. We present ferromagnetic semiconductor properties in Al₂O₃ system, which is electrically an insulator and non-magnet, by modifying lattice structure and lattice defects in the process of non-magnetic Ga ion doping, Ag ion beam irradiation, and implantation of ferromagnetic (Fe, Co) metal ions in bulk and thin film samples. The samples in Rhombohedral structure (R (overline{3 }) c space group) were used for studying structural, electrical, optical and magnetic properties. X-ray photoelectron spectroscopy was used for information of the surface chemical state (elemental composition, chemical bonding, charge state of the ions, defects and vacancy) of the samples. The SRIM (Stopping and Range of Ions in Matter) calculations were used to estimate the ion-beam induced defects. The optical band gap values in the range of 3.6–4.5 eV confirmed wide band gap semiconductor nature of the samples. The ferromagnetic properties at room temperature were confirmed through magneto-optic Kerr effect (surface magnetic coercivity 530–850 Oe) and dc magnetic measurement (bulk magnetic coercivity 25–106 Oe and saturated magnetization 0.09–37 memu/g). The enhancement of ferromagnetic properties in Al₂O₃ based samples have been understood in terms of defect induced local spin order at the surface and bulk structure of the samples, activated during material synthesis.

We theoretically study the anomalous proximity effect in a clean normal metal/disordered normal metal/superconductor junction based on a Rashba semiconductor nanowire model. The system hosts two distinct phases: a trivial helical phase with zero-energy Andreev bound states and a topological phase with Majorana bound states. We analyze the local density of states and induced pair correlations at the edge of the normal metal region. We investigate their behavior under scalar onsite disorder and changing the superconductor and disordered region lengths in the trivial helical and topological phases. We find that both phases exhibit a zero-energy peak in the local density of states and spin-triplet pair correlations in the clean limit, which we attribute primarily to odd-frequency spin-triplet pairs. Disorder rapidly splits the zero-energy peak in the trivial helical phase regardless of the lengths of the superconductor and disordered normal regions. The zero-energy peak in the topological phase shows similar fragility when the superconductor region is short. However, for long superconductor regions, the zero-energy peak in the topological phase remains robust against disorder. In contrast, spin-singlet correlations are suppressed near zero energy in both phases. Our results highlight that the robustness of the zero-energy peak against scalar disorder, contingent on the superconductor region length, serves as a key indicator distinguishing trivial Andreev bound states from topological Majorana bound states.

In this paper, we use the quantum renormalization group method to study the quantum entanglement and phase transitions of the XY system with the transverse magnetic field and discuss the relations between the entanglement and the magnetic field B, the anisotropy parameter (gamma ), and particle number N. The quantum phase transition point of the system can be found through the strange behavior entangled at a certain point, and the relationship between the entanglement and the critical exponent of the correlation length can also be found. The results show that when the magnetic field is fixed, there is a maximum value of entanglement at the critical point (gamma =0), and with the increase of the number of iterations, the maximum value of entanglement gradually increases and approaches one. In addition, we find that (gamma ) has an inhibiting effect on entanglement, and B has a promoting effect on entanglement. At the thermodynamic limit, entanglement exists only at the critical point, in the region where (gamma ne 0), the system corresponds to the Ising-like phase, and at (gamma =0), it corresponds to the spin liquid phase. By studying the entanglement derivatives, we also find that there are two extreme values of the first derivative, and with the increase of the number of iterations, the extreme point gradually approaches the critical point. The first derivative of the entanglement exhibits a nonanalytic behavior at the critical point, indicating that the system has a second-order phase transition. Finally, the scaling behavior of entanglement at the critical point is detected, and the critical exponent of entanglement equals one.

Cobalt ferrite (CoFe₂O₄) nanoparticles are gaining attention in biomedical science for applications in imaging, drug delivery, and cancer therapy. As a hard magnetic material, CoFe₂O₄ exhibits moderate magnetism and high coercivity, 1235 Oe–2.2 kOe at room temperature, up to 10.5 kOe at low temperatures. Its saturation magnetization decreases with smaller particle sizes, ranging from ∼69 emu/g for larger particles to ∼35 emu/g for smaller ones. CoFe₂O₄ crystallizes in a cubic spinel (AB₂O₄) structure, with a lattice parameter of 8.358 Å. Core–shell architectures enhance thermal stability up to 650 °C, while thermogravimetric analysis confirms stability up to 600 °C. This review explores recent advances in synthesis techniques, such as sol–gel and hydrothermal methods, which have enabled precise control over size, shape, and magnetic properties, optimizing CoFe₂O₄ for biomedical applications. Functionalization strategies, including polymer coatings and biomimetic approaches, enhance biocompatibility and targeted therapeutic performance. One promising innovation is cell membrane coating, which improves immune evasion and drug delivery. By exploring these advancements and addressing the barriers to clinical implementation, this review provides insights into how CoFe₂O₄ nanoparticles could become a key player in the future of nanomedicine.

Graphical Abstract

Biofunctionalized CoFe₂O₄ nanoparticles for targeted theranostics

Hexaferrites’ magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements. We report the phase, microstructural analysis, and magnetic behavior of La-Ce co-doped ferrites with a wide range of compositions, including strontium ferrite [SrFe_12-x(La_0.5Ce_0.5)_xO₁₉] and cobalt ferrite [CoFe_2-x(La_0.5Ce_0.5)_xO₄] with varying La-Ce contents (x = 0.0–0.4) using a modified co-precipitation method at room temperature. The results confirmed the hexagonal and cubic structure for La-Ce co-doped strontium and cobalt ferrite compounds, respectively. Morphological studies show particles with a rod-like to plate-like morphology, featuring irregular edges and a moderate degree of agglomeration, suggesting anisotropic grain growth. The lattice parameters a (lattice constant in the basal plane) and c (lattice constant along the vertical direction) for strontium ferrite decrease from 5.84 to 5.20 Å and 23.01 to 21.92 Å, respectively, while for cobalt ferrite they increase from 8.29 to 8.38 Å. The optimum magnetic investigations include saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) up to 71.6 emu/g, 30 emu/g, 1284 Oe, and 39 emu/g, 16 emu/g, and 349 Oe with 10% La-Ce substitution for Fe in strontium and cobalt ferrite, respectively. Thirty percent La-Ce substitution for Fe in cobalt ferrite results in an unexpected increase in M_s (50.92 emu/g) and M_r (20.86 emu/g) that could be attributed to the cation redistribution. The M_r/M_s ratio decreases with the increase of La-Ce contents in both compounds, which is attributed to the reduced exchange interaction between magnetic particles. The moderate values of magnetic parameters make them suitable for permanent magnets in motors and generators, loudspeakers, and audio equipment. 

First-principles calculations, combined with the supercell approach, are employed to investigate the effects of atomic disorder on the electronic properties of the CoFeMnAl quaternary Heusler alloy (LiMgPdSn-type). The ordered alloy is a half-metallic ferromagnet; its moment obeys the Slater-Pauling rule with T_C > 300 K. We analyse twelve antisite and six swap disorder configurations. Calculations show that the Fe_Mn antisite is the most energetically favourable defect (−1.25 eV), followed by the FeCo antisite and the MnAl swap. The disorder generally contracts the spin-down gap. Half-metallicity is largely preserved but completely lost for Co_Al, Co_Mn antisite and CoAl, CoMn swap defects. Disorder has a significant effect on the magnetic moment and Curie temperature. The Fe_Mn antisite gives 3.12 µ_B, which is very close to the experimental value of 3.10 µ_B. This study demonstrates the importance of considering disorder when predicting the properties of Heusler alloys.