Journal of Superconductivity and Novel Magnetism最新文献

Here, we present the preparation of (NiFe_2−xCr_xO₄), with x = 0.0, 0.1, 0.2, 0.3 and 0.4 nanoparticles using a green synthesis method, employing the extract of Aegle marmelos (Bel leaves) as biogenic green fuel. The single-phase production having an FCC-type simple cubic spinel structure was verified by XRD analysis. The prepared nanoparticles exhibit crystallite sizes of 14 to 8 nm. The lattice constant (a) calculated from XRD data decreased from 8.346 Å to 8.307 Å. The formation of spherical grains with some agglomeration was observed through FE-SEM analysis. The surface area determined by BET analysis increases with Cr³⁺ content and ranges from 33.62 m²/g to 59.32 m²/g. The band gap energy calculated using the Tauc plot was in the range 1.57 eV-1.74 eV. Saturation magnetization decreases with Cr³⁺ content. The low coercivity values suggest the superparamagnetic nature of the prepared nanoparticles. No systematic dependence of antibacterial properties of the synthesized nanoparticles was found against Gram-positive (S. Aureus and B. Subtilis) and Gram-negative (E. coli, K. Pneumonia) bacteria for varying Cr³⁺ content. However, the sample with x = 0.2 exhibits enhanced antibacterial activity compared to the other compositions.

The (Nd_10.23Pr_2.56Fe_69.77Co_11.63B_5.81)_100−xCu_x (x = 0–2.0) alloy ribbons were fabricated by melt-spinning technique at 15 m/s, and their hard magnetic performance and microstructure were systematically examined. The experimental results indicate that the intrinsic coercivity (H_ci) initially increases significantly with minor Cu addition, followed by a gradual decrease at higher Cu contents, while both the remanence (B_r) and maximum magnetic energy product ((BH)_max) exhibit a declining trend. Notably, the x = 0.5 alloy achieves the highest intrinsic coercivity of 1260 kA/m, representing a 40.6% improvement compared to the Cu-free alloy. Cu addition results in a marked increase in the grain size. Transmission electron microscopy (TEM) analysis shows that a minor Cu addition has a dramatic effect on the average grain size, enlarging it from 19 ± 1 nm (x = 0) to 60 ± 1 nm (x = 0.5). The mechanism of coercivity improvement induced by Cu addition is discussed by the observed intergranular phase. A distinct ferromagnetic intergranular phase enriched in Nd, Pr, and Cu is observed in the x = 0.5 alloy. The ~ 8 nm-thick intergranular phase exceeds the ferromagnetic exchange interaction length (over 4.18 nm) between 2:14:1 grains, thereby weakening ferromagnetic exchange coupling interaction and enhancing coercivity.

Sol-gel synthesized Zn_0.1Co_0.9Fe₂O₄ was characterized extensively for its structural, magnetic, and optical and dielectric properties in terahertz frequencies. X-ray diffractometry confirmed the pure cubic spinel phase (space group: Fd-3 m). Rietveld analysis in consonance with the room temperature ⁵⁷Fe- Mössbauer data confirmed the inverse spinel structure. Field and temperature dependent magnetization revealed typical ferrimagnetic behaviour with a decent saturation magnetization of 88 emu/g. Terahertz time-domain spectrum in frequency range of 0.3–2.0 THz demonstrated a nearly constant refractive index ~ 2.95 and a low extinction coefficient, indicative of weak absorption and minimal dielectric loss. The real part of the complex dielectric permittivity exhibited remarkable stability (~ 8.94), while the imaginary part displayed negligible dispersion across the measured frequency range. These results demonstrate that low-level Zn substitution effectively tailors the electromagnetic response of cobalt ferrite, positioning Zn_0.1Co_0.9Fe₂O₄ as a promising candidate for high-frequency applications.

Lead-based halide perovskites, despite their remarkable optoelectronic properties, suffer from significant drawbacks, including toxicity and environmental instability, which hinder large-scale deployment in clean energy technologies. To address these concerns, lead-free halide perovskites have emerged as sustainable alternatives, offering comparable performance with reduced ecological and health risks. In this work, we present a comprehensive investigation into the structural, electronic, elastic, optical, and photocatalytic properties of the lead-free halide perovskites KSiI₃ and RbSiI₃. The formability and mechanical stability of both compounds were confirmed via tolerance factor and elastic constants, while the AIMD simulations confirms the thermal stability of both materials at 300 K. HSE functional was used to accurately capture their electronic and optical characteristics. It is found that KSiI₃ and RbSiI₃ are direct band-gap semiconductors (1.44 eV, 1.47 eV), highlighting their potential for photovoltaic applications. Furthermore, the photocatalytic behavior was examined, highlighting the influence of pH on the valence and conduction band edges, confirming that both materials meet the energetic requirements for water-splitting reactions, thereby demonstrating their suitability for photocatalytic hydrogen production.

Magnetic flux density (B) is traditionally interpreted as a continuous field whose flux lines form closed loops, as prescribed by Maxwell’s equations. This description is well justified in macroscopic systems, where large ensembles of magnetic dipoles produce statistically smooth fields through spatial averaging. At the nanoscale, however, where only a limited number of dipoles may contribute, the conditions underlying this continuum interpretation become less clear. Here, we reexamine the meaning of magnetic flux density from a classical-statistical perspective, focusing on finite ensembles and isolated magnetic particles. We show that as the number of contributing dipoles decreases, ensemble averaging becomes insufficient to support a statistically stable, coarse-grained field description, even though the underlying electromagnetic fields remain well defined and fully consistent with Maxwell’s equations. In this regime, magnetic flux density retains its formal definition, but its interpretation as a robust macroscopic observable becomes strongly dependent on fluctuations and specific dipole configurations. This framework introduces a quantitative criterion based on a critical particle number and provides a consistent description of the transition from ensemble-averaged magnetostatics to discrete dipole behavior. The results clarify the limits of continuum field interpretations at the nanoscale and offer a unified perspective for understanding isolated nanoparticles, small dipole ensembles, and the emergence of classical magnetic behavior from discrete microscopic sources.

Magnetic materials with thermally enhanced saturation magnetization (M_S) are very rare but critically important, as they help resist the thermal degradation of magnetic properties caused by the disruption of magnetic ordering at elevated temperatures. This paper summarizes magnetic materials that exhibit anomalous thermal enhancement of saturation magnetization. Particularly, a solid-state reaction method was developed for large scale synthesis of antiperovskite Mn_4+xC, which is the latest system that exhibits thermal-enhanced magnetization. The neutron diffraction results indicate a ferrimagnetic structure of Mn₄C, in which the face-centered Mn moments (~ 1.122(12)µ_B) vary little with temperature while the cornered Mn moment decreases from 3.227(15)µ_B at 10 K to 3.187(14)µ_B at 300 K, resulting in the increasing saturation magnetization with increasing temperature. A total energy calculation on the Mn₄C unit cell suggests an easy axis of [111]. Our theoretical and neutron results agree satisfactorily with the measured magnetization of Mn₄C samples. This work provides a more effective synthesis method of Mn₄C, a better understanding to the origin of positive temperature coefficient of magnetization in Mn₄C, and a method to control the dM_S/dT of Mn_4+xC.

This study presents a comprehensive computational investigation of the structural, electronic, optical, and thermoelectric properties of PtTaAl half-Heusler compound for potential clean energy applications. Using density functional theory (DFT) within the WIEN2k computational framework, supported by the PBE-GGA and mBJ exchange–correlation approximations, the structural stability of PtTaAl was examined across α, β, and γ atomic configurations. Volume optimization and formation-energy analysis reveal that the γ-phase is the most thermodynamically stable configuration, exhibiting negative formation energy that confirms the feasibility of experimental synthesis. Electronic band structure calculations show that PtTaAl behaves like a direct-band-gap semiconductor with a band gap of 0.60 eV (PBE-GGA) and 0.71 eV (mBJ). Density of states analysis further indicates that the d-states of Pt atoms dominate contributions near the Fermi level. Thermoelectric properties, computed using BoltzTraP based on semiclassical Boltzmann transport theory, demonstrate that PtTaAl exhibits promising thermoelectric behavior. The results highlight the material’s strong suitability for medium-to-high-temperature waste-heat recovery and renewable energy conversion. Optical analysis further confirms the potential of PtTaAl for optoelectronic applications. Overall, this research provides a detailed computational report on PtTaAl, establishing it as a viable and efficient candidate for thermoelectric and clean-energy technologies. The findings also create a solid foundation for future experimental validation and materials design involving half-Heuslers.

We report a systematic study of the structural and magnetic properties of rare-earth sesquioxides Yb₂O₃, Er₂O₃, and Dy₂O₃ across a broad range of particle sizes obtained via co-precipitation and subsequent thermal annealing (500–900 °C). X-ray diffraction analysis reveals progressive grain growth with increasing temperature, with Dy₂O₃ exhibiting notably faster coarsening than Yb₂O₃ and Er₂O₃. Temperature-dependent susceptibility measurements indicate Curie-type paramagnetism for all compounds, while low-temperature anomalies suggest contributions from finite-size effects, crystal-field splitting, or residual defects. Field-dependent magnetization at 5 K demonstrates a clear size dependence for Yb₂O₃ and Er₂O₃, where the apparent saturation increases with particle size due to the reduction of surface disorder and the recovery of the full rare-earth moment. In contrast, Dy₂O₃ shows nearly size-independent magnetization, which can be associated with its larger intrinsic moment and strong single-ion anisotropy, and rapid attainment of bulk-like grain sizes. These results highlight the interplay between particle size, surface effects, and crystal-field stabilization in determining the magnetic response of rare-earth oxides and provide guidelines for tailoring nanoscale magnetism in functional materials.

In this study of Fe_2-xCo_xMnAl Heusler alloys, we analysed several key properties such as electronic, magnetic and optical properties including the formation energy, electronic energy band gap, magnetic moment and spin polarization (SP). These properties were studied to understand the half-metallic stability as the lattice parameter changed. The alloys consistently maintained the total magnetic moments (M_Total) predicted by the Slater-Pauling rule (SPR), with values of 2.0 μ_B for x = 0.0, 2.5 μ_B for x = 0.5, 3.0 μ_B for x = 1.0, 3.5 μ_B for x = 1.5, and 4.0 μ_B for x = 2.0, across a wide range of lattice variations. Value of SP was observed 100% with half-metallic ferromagnetic (HMF) behaviour within specific lattice ranges for x = 0.5, this behaviour was observed between 5.40–5.70 Å; for x = 1.0, it was seen between 5.35–5.55 Å; for x = 1.5, the range was 5.30–5.60 Å; for x = 2.0, it occurred between 5.25–5.55 Å. Their ability to maintain a stable half-metallic character over a broad spectrum of lattice parameters also makes them strong candidates for applications in spintronics based devices. Optical characteristics of the Fe_2-xCo_xMnAl (x = 0 to 2) alloys are investigated in terms of optical Reflectivity R(ω), optical conductivity σ(ω), Energy loss L(ω), Absorption coefficient I(ω), real and imaginary parts of the dielectric function (i.e. ε₁(ω) and ε₂(ω) respectively), refractive index n(ω) and extinction coefficient K(ω) provided these materials for applicable in making solar cells and optical switches in photovoltaic device applications.

YBa₂Cu₃O₇₋_δ (YBCO) high-temperature superconductors exhibit enhanced flux pinning capabilities along with high critical temperature (T_c). An improvement in flux pinning and, consequently, the critical current density (J_c) can be achieved by tailoring the precursor phases and their microstructures. In this study, we compare the microstructural modifications of Y₂BaCuO₅ (Y-211) secondary phase particles via ultrasonication processing in de-ionized water (DIW) and ethanol on the superconducting properties of bulk YBCO superconductors.Y-211 precursor powders are engineered by subjecting to high-energy ultrasonication at 450 W for 30 min in de-ionized water and Ethanol. This ultrasonication treatment leads to the formation of nanoscale, surface-modified Y-211 particles, characterized by high surface reactivity and defect density. These pre-treated Y-211 powders are utilized to grow YBCO single grains employing top-seeded infiltration growth (IG) process. Electron microscopy analysis on YBCO bulks revealed a homogeneous microstructure with well-dispersed Y-211 inclusions and embedded sub-phases within the YBCO matrix. Superconducting transition measurements show sharp onset at the temperature of ~ 92 K. The self-field J_c at 77 K enhances to 90 kA/cm² using ultrasonically DIW treated Y-211 powders compared to Ethanol treated (72 kA/cm²) YBCO superconductors. These findings validate the effectiveness of ultrasonically engineered RE₂BaCuO₅ precursors in tailoring flux pinning characteristics and enhancing the performance of REBa₂Cu₃O₇₋_δ bulk superconductors.