Journal of Superconductivity and Novel Magnetism最新文献

In recent work (Bud’ko et al. Supercond. Sci. Technol. 37, 065010 2024), Bud’ko et al. present experimental results for trapped magnetic flux for a tiny sample of a type II superconductor, (CaKFe_4As_4). The paper aims to provide evidence in support of the interpretation that similar measurements performed in samples of hydrogen-rich materials under high pressure by Minkov et al. (Nat. Phys. 19, 1293 2023) are conclusive evidence (Eremets Nat. Sci. Rev. 11, nwae047 2024) for superconductivity in hydrides under pressure. Here, we point out that the new evidence presented by Bud’ko et al. (Supercond. Sci. Technol. 37, 065010 2024) further supports our interpretation (Hirsch and Marsiglio J. Supercond. Nov. Magn. 35, 3141–3145 2022; Hirsch and Marsiglio Phys. C 620, 1354500 2024) that the reported measurements of trapped flux on hydrides under pressure (Minkov et al. Nat. Phys. 19, 1293 2023) are not consistent with what would be expected from a superconducting sample.

We investigated the magnetic, magnetocaloric, and hysteresis characteristics of the antiperovskite material Fe(_{3})ZnN by employing the mean-field approximation method. The findings indicate that magnetization gradually declines with rising temperature, whereas the application of an external magnetic field elevates the critical temperature (T_{c}) by promoting greater alignment of the magnetic moments. A peak in the magnetic entropy change (-Delta S_{m}), at (T_{c}), indicating a significant magnetocaloric effect, ideal for magnetic refrigeration applications. Additionally, the relative cooling power (RCP) exhibits a linear increase with the strength of the magnetic field. The hysteresis analysis reveals a gradual decrease in coercivity and remanence with rising temperature, ultimately leading to the disappearance of the hysteresis loop above (T_{c}), signaling a transition to the paramagnetic phase. These findings suggest that the Fe(_{3})ZnN compound holds promise as a candidate material for magnetic refrigeration applications.

The high-pressure phase diagram of Magnesium (Mg) has attracted significant attention due to its relevance as a constituent of Earth’s inner core (IC), where it profoundly influences physical behavior and properties under extreme conditions. A recent study has revealed multiple crystal structure transitions in Mg, including the emergence of non-close-packed phases at extreme pressures. We investigate the electronic structure of simple cubic (SC) Mg under extreme pressure using Density Functional Theory (DFT) calculations. At 1320 GPa, our analysis shows that charge density accumulates at the center of the unit cell, increasing as pressure rises. The electron localization function (ELF) reveals that electrons are not just confined to atomic sites but also extend into interstitial regions, suggesting a shift in bonding character driven by p-d-orbital contributions. Additionally, the electronic band structure and density of states (DOS) confirm that Mg remains metallic at this pressure. A distinct flat band appears along the X-M path in the Brillouin zone, indicating enhanced electronic correlations that could influence the transport properties of Mg. These results highlight how extreme compression reshapes electronic interactions, potentially leading to novel high-pressure phenomena.

In this study, we investigated the relationship between excess conductivity and the local structure of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ ((Bi, Pb)-2223) polycrystalline samples. A series of (Bi, Pb)-2223 + LSMO composites (0 – 1.5 wt%) were synthesized using the conventional solid-state reaction method. The critical temperature (T_c) determined from the temperature-dependent resistivity curves decreased with increasing LSMO content, from 106.65 K for the pure sample to 102.48 K to the 15 wt% sample, except for the 10 wt% sample, which exhibited a rise comparable to the pure sample. To elucidate the mechanisms affecting T_c, we applied the Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) theories. We identified the Lawrence-Doniach temperature (T_LD) as the crossover point at which the system transitions from 2 to 3D fluctuations in the mean field region (MFR). Our calculations of excess conductivity within the MFR enabled us to quantify microscopic parameters such as the coherence length along the c-axis (({xi }_{c})), interlayer coupling strength ((J)), and interlayer coupling distance ((d)), revealing trends in T_c associated with LSMO addition in the (Bi, Pb)-2223 system. The local atomic structure of the CuO₂ plane was characterized using X-ray absorption fine structure measurements at the Cu K-edge. We observed contrasting behaviors between the Cu–O and Cu-Ca bonds, indicating weakened interaction between the CuO₂ superconducting layer and the space layer. Meanwhile, the Cu-Sr bond exhibited suppression or elongation due to LSMO addition. Notably, in the 10 wt% sample, the bond lengths from the absorbing atom were similar to those in the pure sample, suggesting an inhomogeneous distribution of LSMO in the samples. These findings indicate that local structural alterations due to LSMO addition decrease the carrier supply to the CuO₂ layers, thereby affecting the superconducting properties of the (Bi, Pb)-2223 system.

KNi(PO₃)₃ was successfully synthesized by solid-state method and the magnetic properties were characterized. The crystal structure of KNi(PO₃)₃ belongs to trigonal crystal system with space group R3, where Ni²⁺ ions form the distorted honeycomb-lattice within the ab-plane stacking in the “ABAB” type fashion along the c-axis. Magnetization measurements reveal the presence of antiferromagnetic (AFM) interaction with Curie Weiss (CW) temperature θ_CW =  − 12.905 K but without long-range magnetic order down to 2 K. Notably, the CW fitted effective moment µ_eff = 3.35µ_B and saturated magnetization M_S = 2μ_B/Ni²⁺ at 2 K support KNi(PO₃)₃ as an S = 1 spin system. Intriguingly, the zero-field specific heat exhibits a broad peak maximized at ~ 2.5 K indicating the onset of short-range spin correlation between Ni²⁺ ions, while the integrated magnetic entropy (S_mag) is close to the expected Rln3 for S = 1 system, indicative of large spin fluctuation below 2 K driven by spin frustration.

FeSe(11) family has a simple crystal structure belonging to iron-based superconductors (FBS) and has many stable phases including hexagonal and tetragonal structures, but only the tetragonal phase exhibits the superconductivity. In this study, we have investigated the effects of chemical pressure induced by As-doping at Se sites in the FeSe system by preparing a series of FeSe_1-xAs_x (x = 0.005, 0.01, 0.02, 0.05, 0.1 and 0.2) bulks. A broad characterization has been performed on these samples using structural, microstructural, transport and magnetic measurements. The obtained lattice parameters are increased by As-doping, which suggests the successful insertion of As at Se sites into the tetragonal lattice for low doping contents up to 5%, whereas the higher As substitution appears in the form of the FeAs impurity phase. The temperature dependence of the resistivity of all samples has similar behaviour and depicts the highest onset transition temperature of around 11.5 K, but the zero resistivity is not reached until the measured temperature of 7 K, which could be due to the presence of the impurity phases. Our study suggests that a dopant with a large ionic radius, i.e. arsenic, promotes the formation of the hexagonal phase of the 11 family and is effective for a small amount of doping level for the superconducting properties, whereas higher As-doping levels reduce the superconducting properties.

In this research, the structural, electronic, optical, and magnetic characteristics of InAlN and Gd-doped InAlN were analyzed using the PBE-GGA and GGA + U method respectively. A first principle investigation using density functional theory (DFT) has been conducted to examine for these properties. The formation energy calculations indicate that the Gd atom preferentially substitutes for the In site. The lattice parameters of the InAlN alloy increase upon doping with Gd due to the larger ionic radius. Compared to InAlN, the Gd-doped InAlN becomes an indirect band gap semiconductor with a reduced band gap. Within the GGA + U framework, the total magnetic moment is precisely characterized by an integer value. Due to the presence of partially filled 4f electrons in Gd, the magnetic moment 6.85 ({mu }_{B}) primarily originates from the Gd atom, with minimal contributions from the In, Al, and N atoms. The calculations of optical properties revealed that Gd-doped InAlN exhibit high absorption rate in the UV region. The real and imaginary parts of the dielectric function, as well as the refractive index and extinction coefficient, have been calculated and displayed for photon energy up to 14 eV. This theoretical analysis may aid in the design of new optoelectronic devices and future solar cell generations.

Sol–gel auto combustion was used to create polycrystalline ZnMn_2-xLa_xO₄ nanoparticles, where x = 0.0, 0.05, 0.1, and 0.15 zinc manganite. La concentration, structural, electrical conductivity, magnetic, and electrochemical properties were found to be strongly correlated. ZnMn₂O₄ and other manganese-rich spinels have a tetragonal spinel structure due to the octahedral MnO₆ unit’s Jahn–Teller distortion. ZnMn_2-xLa_xO₄ oxides progressively change to a cubic spinel structure as more La occurs in the place of manganese. Expanding La substitution causes the lattice parameter c to drop from 9.2178 to 9.2158 A° and the lattice parameter a = b to rise from 5.6869 to 5.9107 A°. For rare-earth dopants such as lanthanum, substitution doping is necessary due to their (La) large ionic radii in comparison to manganese and zinc. Smaller particles would form as a result of doping materials like La form Zn and Mn, which would change particle mobility. Differences between zinc manganite and zinc manganite doped with La may be due to lattice strain and structural disorder. The conductivity value from both pure and (0.15%) doped samples rises from 16.46 × 10⁻⁴ S cm⁻¹ to 323.89 × 10⁻⁴ S cm⁻¹ with increasing La substitution. The enhanced electrochemical performance is caused by the formation of a La doped ZnMn₂O₄ which can suppress the volume expansion during the charge–discharge process.

Antiferromagnetic Kagome semimetal FeSn has gained significant attention due to the presence of topological flat bands and Dirac fermions. There has been immense interest to tune the bands with doping in FeSn for enhancing the magnetic and transport properties. Here, we report an experimental study of transport, magnetization, and electronic structure of Fe(_{1-y})Co(_y)Sn as a function of Co-doping concentration (y). Variation in the temperature-dependent resistivity with increasing y is associated with the increase in spin-dependent scattering. Co doping in FeSn gives rise to canted antiferromagnetism with the decrease in the Neel transition temperature ((T_{N})). The local moment of Co and Fe atoms has been estimated from the analysis of 3s core levels. The decrease in (T_{N}) with increasing y is due to the decrease in the local moment of Fe atoms. The systematic shift in the valence states away from the Fermi level ((E_{F})), and the valence band broadening with the increase in y indicate an increase in the electron correlation and hybridization effects in Fe(_{1-y})Co(_y)Sn. An increase in both electron correlation and hybridization with doping leads to the strong magnetic interaction between the local moments of Fe and Co atoms which gives rise to the canted antiferromagnetism in Fe(_{1-y})Co(_y)Sn.

The features of the crystal structure and spin order in the ground state of two samples of layered honeycomb oxides of the same stoichiometric composition Li₂Ni₂TeO₆ were established by the neutron powder diffraction method. These samples were synthesized by the ion-exchange method from different precursors, Na₂Ni₂TeO₆ and K₂Ni₂TeO₆, having a similar crystal structure, hexagonal space group P6₃/mcm, but with a significant difference in the distances between the layers. Both Li₂Ni₂TeO₆ samples do not retain the structure of the precursors and crystallize into the orthorhombic space group Cmca, with very minor differences in the unit cell parameters. While Li₂Ni₂TeO₆ from the potassium precursor is single-phase, the sample from the sodium precursor appears to be a mixture of two crystal modifications. Its main phase is crystallized in Cmca, and the second phase, 13.6 wt.%, with the same Li₂Ni₂TeO₆ stoichiometry, is more deformed, with monoclinic distortions described by the C2/m space group. The values of the fragments of the fine crystal structure have been calculated. The coherent coupling of the two phases at the unit cell level was shown. The magnetic structures of the investigated samples in the ordered magnetic state at T = 1.5 K have been determined and described in details. A relatively small incommensurability of the magnetic structure is manifested across all three crystallographic directions. The magnetic propagation vector can be represented as k = (1/2-δ₁, 1/2-δ₂, 1/2-δ₃) at small values of δ, i.e., the magnetic unit cell is almost doubled in relation to the crystallographic one. The magnetic order is three-dimensional and represents an antiferromagnetic ordering of magnetic Ni ions in honeycomb ab planes of the stripe type with magnetic moments coming out of the honeycomb plane. The influence of the presence of a mixture of phases of stoichiometric composition but different crystal structures on the magnetic ordering of Li₂Ni₂TeO₆ has been studied.