Journal of Superconductivity and Novel Magnetism最新文献

Minimization or tailoring of magnetic anisotropies in the order of magneto-crystal, magneto-elastic and external field-induced anisotropies are effective way of improving soft-magnetism in nanocrystalline alloys. The recently developed Fe-rich nanocrystalline alloys have been found to exhibit positive magnetostriction behaviour and magnetic coercivity twice that of FINEMET alloys, after optimal annealing. This makes uniaxial tensile-stress annealing a promising method to improve the soft-magnetism of these alloys. In that direction, the present study investigates the influence of tensile stress annealing on structure, soft-magnetic, magnetostriction and core-loss properties of Fe-rich Fe₈₃Si₂B₉P₄Nb₁Cu₁ nanocrystalline ribbons. The samples were uniformly annealed at 480 °C for 4 min with varying uniaxial tensile stress ranging from 0 to 180 MPa. The XRD results showed that all annealed ribbons had a uniform nanocrystalline microstructure consisting of a BCC α-Fe(Si) phase with an average grain size of less than 20 nm, irrespective of the applied stress. However, the magnetic properties were highly sensitive to the magnitude of the tensile stress during nanocrystallization annealing. The optimal tensile stress ranging from 90-140 MPa resulted in the best combination of soft-magnetic properties (11–12 A/m) and high squareness ratio (0.8-0.9). These ribbons also depicted longitudinal anisotropy (K_u ≤ 0). On the other hand, tensile stress above 165 MPa resulted in the deterioration of magnetic properties (> 24 A/m) and transverse anisotropy behaviour (K_u > 0). The transformation of tensile stress-induced anisotropy from longitudinal to transverse was characterized by the reduction of the magnetostriction constant and change in the magnetization process. The core-loss plots (50-1000 Hz) showed a reduction for optimal stress-annealed (90-140 MPa) ribbons and a drastic increase for 165-180 MPa ribbons. The study highlights the beneficial role of controlled tensile stress annealing in improving the soft-magnetism of Fe-rich nanocrystalline alloys with positive magnetostriction.

This article reports the successful synthesis of single crystalline two-dimensional thin flakes of NbSe₂. The XRD (X-ray diffraction) pattern of the grown crystal ensured its crystallization in a single phase with a hexagonal structure. The EDAX (energy dispersive X-ray analysis) endorsed the stoichiometry of the as-grown sample. To study the vibrational modes, the Raman spectra were recorded, which exhibited the expected four Raman active modes. The resistance vs temperature measurement showed a well-established superconducting transition (T_c) at 7.3 K. The ZFC (zero-field cooled) and FC (field cooled) magnetization curves, as well as the isothermal M−H (magnetization vs field) measurements, have been performed for both in-plane and out-of-plane H directions. Distinct anisotropy is observed in both magnetization and magneto-transport measurements with field direction, leading to different critical fields (H_c). Out-of-plane magneto-transport data hints towards the existence of a filamentary state. The density functional theory (DFT) has been used to study the band structure of NbSe₂. Although the bulk band structure confirmed metallic behavior, the same of mono-layers of NbSe₂ within the GGA+U framework showed a band gap of 1.17 eV. The article addresses the anisotropy in the electronic and magneto-transport of 2D superconductor NbSe₂.

Barium hexaferrite (BaFe₁₂O₁₉) and Ni–Zn ferrite (Ni_0.6Zn_0.4Fe₂O₄) powders were synthesized using the microwave hydrothermal method. Composite samples with varying ratios {x(Ni_0.6Zn_0.4Fe₂O₄) + (1 − x) (BaFe₁₂O₁₉)} (where x ranged from 0 to 1.0) were prepared through mechanical mixing. The pure and composite samples were subjected to a 4-h heat treatment at 800 °C. The structural characteristics of the pure samples were analyzed using X-ray diffraction (XRD), revealing the hexagonal structure of BaFe₁₂O₁₉ and the spinel structure of Ni_0.6Zn_0.4Fe₂O₄. Morphological properties were investigated using field emission scanning electron microscopy (FESEM). The results confirmed a hexagonal morphology for BaFe₁₂O₁₉, a spherical morphology for Ni_0.6Zn_0.4Fe₂O₄, and a mixed morphology for the composites, with grain sizes ranging from 50 to 200 nm. The optical properties were explored through UV–Vis absorption studies, and the optical energy gap values were determined using the Tauc plots. The magnetic behavior of the samples was studied by analyzing magnetic hysteresis loops. Pure samples exhibited a smooth hysteresis behavior, while composite samples displayed a step-like pattern. A possible relation between the magnetic interaction between the two different materials in the composites was investigated.

The resistive transition between the normal and superconducting states in high critical temperature superconducting materials is characterized by the occurrence of two well-defined stages: a transition in the higher temperature thermal region called pairing transition and another known as coherence transition. In the presence of low magnetic fields, in the first transition, it is possible to identify a genuinely critical fluctuation regime, with Gaussian regimes. The Aslamazov-Larkin model in the 3D regime allows to analyze the amplitude of the order parameter, leading to the determination of parameters such as coherence length and critical field. In the coherence transition, the phase of the order parameter is the relevant quantity that varies between the grains of the system, leading to Josephson-type effects in the intergranular barriers due to the polycrystalline feature of this family of materials. The coherence transition for the sample GdBa₂Cu₃O_7-δ under the application of seven different electric transport currents was studied in this work. The sample was produced by the solid-state reaction and the resistive behavior was determined to perform the paraconductivity analysis and characterizes granularity effects on the superconducting order parameter. A genuinely critical region characterized by dynamic critical exponent z = 4.5 was identified, similar to the value reported for the transition vortex glass – fluid. This paper proposes to identify three-dimensional Gaussian fluctuations in the paracoherent to get a coherence length associated with Josephson effects in the granular barrier and to find a factor related with the Josephson current in function of the seven applied currents.

Silver-doped Bi_1/2Na_1/2-xAg_xTiO₃ (BNAT) ceramics (x = 0.0, 0.025, 0.075, and 0.1) were synthesized using the solid-state reaction (SSR) technique. The structural analysis was performed using the X-ray diffraction (XRD) technique, which revealed the formation of a polycrystalline sample with R3c symmetry. Pristine Bi_0.5Na_0.5TiO₃ (BNT) ceramics exhibited an average crystallite size of ~25.372 nm. Doping a small amount of Ag⁺ ions in place of Na⁺ ions resulted in an improved average crystallite size of ~26.365 nm, as calculated by Debye-Scherrer’s formula. Raman spectra were employed to investigate the vibrational modes of the materials. The FTIR spectra of Ag⁺-doped BNT ceramics displayed two strong peaks at ~971 and 537 cm⁻¹, attributed to the presence of metal-oxygen bonds. Room temperature dielectric constant (ε′) and dielectric loss (tan δ) analyses were conducted in the frequency range of 20 Hz to 1 MHz. Complex impedance and modulus spectroscopic analyses indicated the presence of grain boundary effects alongside the bulk contribution and also confirmed the presence of non-Debye relaxations in the materials.

We investigate plasmon properties in a double-layer graphene structure under the effects of an in-plane external magnetic field within the zero-temperature random-phase approximation. Numerical calculations demonstrate that two plasmon modes exist in the system, corresponding to in-phase and out-of-phase oscillations of charges. The spin polarization number P affects the optical and acoustic plasmon modes and their decay rate differently. As the polarization number increases, the frequency of the acoustic mode slightly decreases while that of the optical mode significantly increases. Besides, the existence of an external magnetic field expands the single-particle-excitation area of the system; therefore, plasmon modes become damped at a smaller wave vector, compared to those in the case of unpolarized systems. The separation between two layers increases (decreases) the plasmon frequency of the acoustic (optical) mode. Finally, we found that background dielectric inhomogeneity decreases the energy and decay rate of plasmon modes of the spin-polarized system.

Breast cancer is one of the deadliest cancers for women, so cell labeling and therapy of breast cancer become imperative. In this work, dextran- and carboxymethyl dextran–coated Fe₃O₄ nanoparticles (Fe₃O₄@DEX and Fe₃O₄@CMD) were well synthesized through the co-precipitation method. The dextran and carboxymethyl dextran coating reduces the average particle size of Fe₃O₄ nanoparticles from 10.9 to 4.0–5.5 nm, and the coated samples exhibit average hydrodynamic diameters ranging from 31 to 110 nm. The coating promotes the dispersibility of nanoparticles. Saturation magnetization is reduced from 60.3 to 5.6–7.1 emu/g in the coated MNPs due to the large weight ratio of the coating layer and the decrease in particle size. Hemolysis and cytotoxicity assay results indicate the excellent biocompatibility of Fe₃O₄ nanoparticles. The cellular uptake assay confirms that both dextran- and carboxymethyl dextran–coated Fe₃O₄ nanoparticles are easily taken in by breast cancer cells. Comprehensively considering dispersion, biocompatibility, and cellular uptake, the Fe₃O₄@CMD is more suitable for application in the bio-labeling of breast cancer cells. The SAR values of the Fe₃O₄@DEX and Fe₃O₄@CMD range from 19.2 to 30.7 W/g. The SAR value is mainly influenced by the hydrodynamic diameter in the coated samples. The Fe₃O₄@CMD20 shows the maximum SAR value of 30.7 W/g and has potential application in magnetic hyperthermia therapy.

A comprehensive analysis on conventional rod core fluxgate magnetometer has been done by designing multiple designs with varying number of turns of excitation coil (from hence will be referred to as EXC) and pick-up coil (PC) as well as different core diameter have in Ansys Maxwell and their electromagnetic simulations have been carried out, the results were analysed and are reported in this paper. Also, the current sweep analysis, frequency sweep analysis has been done to study the behaviour of the ferromagnetic core for different magnitudes of excitation current as well as for studying the variation in output induced voltage for different frequencies of the input excitation current. Finally, the electromagnetic simulation of 100 turns rod core design with different ferromagnetic core materials such as iron, ferrite, Metglas 2605 HB1M and Mu-metal has been done to study the sensor performance in terms of sensitivity. The results of all these conducted studies have been included in this paper.

The method of linearized full-potential augmented plane waves based on density functional theory (DFT) is employed to investigate the structural, elastic, magnetic electronic, and thermoelectric properties of the cerium-based half-Heusler alloy FeCeSi. The exchange correlation functional is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE) and the Tran-Blaha-modified Beck-Johnson (TB-mBJ) as implemented in the Wien2k package. According to our results, we have discovered that the material studied is mechanically stable, which means that this compound can be synthesized experimentally. Furthermore, FeCeSi exhibits a half-metallic behavior obeying the Slater-Pauling rule with an integer magnetic moment of 2 μB. The electronic band structures and density of states confirm the half-metallic character with an indirect band gap equals to 0.51 eV and 0.59 eV for GGA-PBE and TB-mBJ approximation, respectively. For the study of the thermoelectric parameters, such as Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), and figure of merit (ZT), the Boltzmann transport equations within the framework of DFT have been used. Significant values for the figure of merit and Seebeck coefficient indicate promising candidate for useful thermoelectric applications for FeCeSi alloy. So far, no experimental or theoretical investigations have been carried out on the half-Heusler alloy FeCeSi. Accordingly, our theoretical results concerning structural, elastic, electronic, magnetic, and thermoelectric properties will probably be confirmed by experimental investigations.

A high sensitivity photonic crystal fiber (PCF) magnetic field sensor based on Sagnac interferometer is proposed. All the air holes of the PCF are completely filled with the magnetic fluid (MF), which is a magnetic liquid material. The sensing performance of PCF is simulated and analyzed by using finite element method (FEM). It is found that the effects of wavelength λ, phase birefringence B(λ,H), and group birefringence B_g(λ,H) on the sensitivity are very significant. The two dip points in this spectrum show a red shift and a blue shift as the refractive index of the magnetic fluid increases, respectively. This magnetic field sensor obtains the average sensitivity of 889.5 pm/Oe (111,684.9 nm/RIU) and −994.3 pm/Oe (−124,839.5 nm/RIU) in the range from 90 to 240 Oe.