Journal of Superconductivity and Novel Magnetism最新文献

This paper proposes a highly compact, two-branch-type lumped-parameter equivalent circuit for broadband core loss estimation in high-frequency magnetic components. The parallel architecture is streamlined to its physical essentials: a generalized Play operator synthesized via resistance and Zener-diode branches to model the complete quasi-static magnetization curve up to the saturation flux density ((varvec{B_{sat}})), and a fractional-order Constant Phase Element (CPE) to natively encode rate-dependent anomalous losses. This decoupled architecture enables fully deterministic parameter extraction: unconstrained Non-Negative Least Squares (NNLS) optimally maps the static hysteresis, while multi-frequency log-log energy regression isolates the dynamic fractional order (alpha ). Validated experimentally from 25 Hz to 5 kHz, the model yields a (varvec{1.22%}) energetic error at 5 kHz and accurately captures complex minor loops and demagnetization trajectories. Its structural sparsity and thermodynamic consistency make it a highly efficient tool for rapid system-level power electronics simulations.

We investigate tunnel ferromagnetic Josephson junctions based on Superconductor-Insulator-thin superconductor-Ferromagnet-Superconductor multilayers. A comparative study of their electrodynamic properties is performed for junctions with niobium and aluminum (Al) electrodes, featuring different ferromagnetic interlayer materials and lateral dimensions ranging from the micrometric to the submicrometric scale. The parameters extracted from the fitting of the current-voltage characteristics using the tunnel junction microscopic model are found to be consistent with those independently estimated from switching current distribution measurements. Submicrometric Al-based devices exhibit electrodynamic properties comparable to those implemented in state-of-the-art transmon qubits and display clear signatures of quantum phase diffusion. The strong agreement between transport modelling and escape dynamics establishes a robust framework for describing hybrid ferromagnetic Josephson junctions consistent with their energy scales and supports their potential integration into superconducting quantum and classical digital circuits.

We report a systematic study of the structural, magnetic, and transport properties of ε-Mn₃Ga (Mn₇₂Ga₂₈), a high-temperature hexagonal D0₁₉ phase (space group P6₃/mmc) that has received little attention relative to its low-temperature η counterpart. X-ray diffraction confirms phase-pure ε-type ordering. Magnetic measurements uncover a series of temperature-driven spin rearrangements: antiferromagnetic ordering at ~ 400 K, a magnetic-state rearrangement near 300 K, a magnetoelastic anomaly around 200 K, and a possible spin-reorientation transition below 50 K. The alloy shows metallic behavior with a resistivity minimum near 40 K and an upturn at lower temperatures, consistent with disorder-induced scattering. Transport measurements reveal a pronounced anomalous Hall effect with a scaling exponent α ≈ 2, indicating dominant intrinsic and side-jump contributions. In addition, an extra Hall signal of 0.441 µΩ·cm appears at 50 K, which cannot be accounted for by the ordinary Hall effect or the measured magnetization, pointing to the possible role of noncoplanar spin textures in the frustrated triangular Mn sublattice. Our results establish ε-Mn₃Ga as a system in which temperature-dependent spin evolution is directly coupled to Hall transport, offering a well-defined antiferromagnetic framework for exploring Berry-curvature-driven phenomena.

We report the growth of high-quality single crystals of the incommensurate spin-ladder system Bi-doped Sr(_{10-x})Ca(_x)Cu(_{17})O(_{29+delta }) using an optimized self-flux pressure technique, exhibiting an enhanced superconducting transition temperature of T(_c) = 87.5 K compared to previous reports [1–5]. The as-grown crystals were systematically characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction (SCXRD) confirming their morphology and chemical homogeneity. Structural refinements confirm the incorporation of a small amount of Bi into the SCCO lattice through partial substitution of Bi(^{3+}) at the Sr(^{2+})/Ca(^{2+}) sites while preserving the orthorhombic crystal structure. Magnetization and resistivity measurements revealed an improvement in the superconducting transition temperature of Bi-doped Sr(_{10-x})Ca(_x)Cu(_{17})O(_{29}) single crystals. The enhanced superconducting T(_c) is likely brought about by the optimized self-flux pressure technique process as well as Bi(^{3+}) substitution at the Sr(^{2+})/Ca(^{2+}) sites resulting in a possible enhanced ladder-hole concentration in Bi-doped Sr(_{10-x})Ca(_x)Cu(_{17})O(_{29}) crystals.

Using the variational approach, the present study probes the magneto-electronic thermal conductivity (METC) of mixed-valence manganite systems Re₁₋ₓAₓMnO₃, where rare earth ions (La, Pr, Nd) are partially substituted by divalent alkaline earth cations (Ca, Sr, Ba). These compounds characteristically display colossal magnetoresistance (CMR). Using a two-band (ℓ-b) Anderson Lattice Model Hamiltonian, we study these materials in the strong electron-lattice Jahn-Teller (JT) coupling regime. This approach is similar to the two-fluid model and (ℓ-b) hybridisation. Key model Parameters such as local coulomb repulsion (U), Hund’s rule coupling (J_H) between e_g and t_2g spins, and hybridisation (V) between ℓ-polarons and d-electrons of the same spin affect METC. We applied the variational method to examine the temperature dependence of electrical resistivity ρ(T) and electronic specific heat C(T) in doped CMR manganites. Our main findings shows: METC increases with temperature, peaks at low temperatures, and decreases at higher temperatures for fixed values of hybridisation ‘V’, Hund’s coupling ‘JH’, and doping ‘x’; When entering the metallic state, METC rises sharply and is strongly influenced by an applied magnetic field, which suppresses the peak and restores lattice thermal conductivity; This anomaly arises from thermal phonon scattering by spin fluctuation, not JT distortion modification at the transition temperature Tc; At low temperatures, METC shows typical crystalline character, with grain boundary scattering the main mechanism limiting heat transfer; and Because of high electrical resistivity, we only considered the electronic contribution to total thermal conductivity. Our qualitative findings align with experimental results.

In this study, a three-axis search coil magnetometer intended for ultra-low-frequency (ULF) magnetic field measurements was designed, developed, and experimentally characterized. The sensor consists of three orthogonally arranged sensing elements, each composed of a ferromagnetic core and an individual pickup coil. Particular emphasis was placed on the optimization of core geometry, pickup coil winding configuration, and axis orthogonality to achieve low-noise performance in the sub-hertz frequency band. The scale factors of the developed sensor were experimentally determined as 126.6 mV/µT, 124.28 mV/µT, and 130.15 mV/µT for the X-, Y-, and Z-axes, respectively. The equivalent magnetic noise spectral density of each axis was measured in the 0.125–5 Hz frequency range using a dynamic signal analyzer under magnetically shielded conditions. The measured noise spectra exhibited power-law behavior in the log–log domain, with spectral slopes of − 1.17, − 0.99, and − 1.19 for the X-, Y-, and Z-axes, respectively. The X- and Z-axis sensors showed nearly parallel spectral responses, while the Y-axis exhibited a slightly flatter trend, most likely due to minor differences in core properties and pickup coil winding numbers. The minimum detectable magnetic field of the proposed sensor was determined as 52.3 pT at 1 Hz and 10.5 pT at 5 Hz. The obtained results demonstrate that the developed three-axis search coil magnetometer provides stable and low-noise performance in the ULF band, designed for the observation of possible pre-seismic ULF magnetic anomalies.

In this study, we present a dual-framework theoretical model that combines a microscopic Heisenberg Hamiltonian and a macroscopic Landau free energy expansion to clarify the magneto-structural phase transitions in Cu-substituted Ni_50−xCu_xMn₃₈Sn₁₂+B(3% at.) ribbons. Experimental results show a marked suppression of the martensitic transformation temperature with Cu substitution, despite only minimal lattice expansion ((:varDelta:a/aapprox:0.15%)). To address this discrepancy, our model demonstrates that the shift in transition temperatures is primarily caused by magnetic dilution rather than purely distance-dependent RKKY interactions. Using an inverse Mean Field Theory approach, we quantitatively demonstrate a systematic reduction in the effective nearest-neighbour exchange integral ((:{text{J}}_{1})) from 12.0 meV to 6.0 meV, resulting from the disruption of exchange paths by non-magnetic Cu (3d¹⁰). Additionally, the macroscopic Landau framework reveals that Cu substitution weakens the magneto-structural coupling term ((:lambda:{Q}^{2}{M}^{2})), significantly lowering the activation energy barrier for the phase transition. At the microscopic level, the presence of fully filled Cu-3d states leads to “orbital dilution” near the Fermi level, suppressing d-d orbital hybridization and alleviating the band-Jahn-Teller instability. This unified model successfully accounts for the reduction in thermal hysteresis, the persistence of field-induced metamagnetic behaviour, and the enhanced low-field actuation capabilities in heavily Cu-substituted Heusler alloys.

A necessary condition for understanding and predicting the properties of any material is knowledge of microscopic parameters which control these properties in a state of thermodynamic equilibrium. One can show (see, e.g., Ref. [1]), that in superconductors these parameters are the radius of the orbital motion of electrons bound in Cooper pairs (R_0) and the radius of the field-induced currents (r_i) caused by precession of the pairs; one more parameter, associated with (r_i), is the number density of Cooper pairs (n_{cp}). In this paper we report on the first measurements of these parameters in a type-II superconductor (niobium) by SANS (small-angle neutron scattering). Other approaches to measuring the microscopic parameters are considered. Our work suggests novel avenues for studying superconductivity, important for disclosing its mechanisms in superconductors of all kinds.

In this paper, based on the invited talk at the Samarkand conference SISM 2026, we discuss first the superconducting phase within the generalized mean field approach with pairing induced both by short-range antiferromagnetic coupling and electron-phonon interaction and secondly the origin of a pseudogap (PG) state in high-(T_c) cuprates. This phenomenon is beyond the standard Fermi liquid state. Already in the beginning of the HTSC era, phenomenological nearly antiferromagnetic Fermi liquid (NAFL) theory has been discussed in the literature to explain nuclear magnetic resonance (NMR) and inelastic neutron scattering data. Within this approach, the PG origin is related to short-range spin fluctuations. To understand how short-range spin correlations effect the electronic structure and magnetic susceptibility in a microscopic approach, we simultaneously studied the low-doping temperature evolution of both single particle spectra and spin correlations using cluster perturbation theory (CPT) and exact diagonalization. We have determined 3 temperature regimes in the normal phase: Fermi liquid, weak PG, and strong PG, and the d-wave superconducting phase formed by a combined action of magnetic and phonon coupling.

The quaternary compound Al_1.5Co_2.5FeGd was melted and synthesized using a vacuum arc furnace. Powder X-ray diffraction and Rietveld refinement were employed to determine its crystallographic parameters. The results reveal that Al_1.5Co_2.5FeGd retains a CaCu₅-type structure (space group P6/mmm, No. 191). The lattice constants are refined to a = 5.1042(3) Å and c = 4.0560(2) Å. The residual factors R_p and R_wp were converged to 8.41% and 10.07%, respectively. Furthermore, magnetic measurements were performed on Al_1.5Co_2.5FeGd under a low applied field of 50 Oe, showing that its Curie temperature T_c is 395.2 K. High-field magnetic characterization further demonstrates that the saturation magnetization M_s, remanence M_r, and coercivity H_c decrease with increasing temperature over the measured temperature range, and weak ferrimagnetic behavior is observed at room temperature. Meanwhile, the hysteresis losses W_h at 2 K and 300 K are 184.58 kJ·m⁻³ and 91.54 kJ·m⁻³, respectively.