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 Ni50−xCuxMn38Sn12+B(3 a/a≈ 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 ( 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 ( λ Q^2M^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.
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 Al1.5Co2.5FeGd 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 Al1.5Co2.5FeGd 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 Rp and Rwp were converged to 8.41
In the current work, Cr-substituted nickel-zinc spinel ferrite magnetic nanoparticles (NPs) with the configuration Ni0.7Zn0.3CrxFe2−xO4 (x = 0.0–0.4) were developed using the extract of Piper nigrum (black pepper) as both a chelating agent and an eco-friendly fuel. X-ray diffraction (XRD) and Rietveld analysis verified that the constructed material exhibits single-phase formation with a cubic spinel structure. Lattice parameter decreases with Cr substitution, from 8.372 Å to 8.356 Å. The formation of the spinel phase was further confirmed by Fourier transform infrared (FTIR) spectroscopy, which revealed two distinct absorption bands within the 400–600 cm− 1 region. Raman spectroscopic investigation identified five distinct vibrational modes. Scanning electron microscopy (SEM) analysis of typical samples showed a compact microstructure composed of uniformly distributed spherical grains. Elemental analysis using (EDAX) spectra revealed the existence of all the desired elements. BET analysis showed an enhanced surface area for typical samples with x = 0.1 and 0.3. The VSM technique was employed to demonstrate the reduction in magnetic properties at room temperature after Cr3+ doping. The band gap energy determined from UV-vis spectroscopy decreases from 1.75 eV to 1.59 eV after doping with Cr3+ ions. Photocatalytic activity was evaluated using methylene blue (MB) under sunlight. The higher photocatalytic degradation activity of the sample with concentration x = 0.3 was 86.10
MgB₂ wires fabricated by the advanced magnesium infiltration process (AMIP) were subjected to different drawing steps and cold high-pressure densification (CHPD) at 0.8 GPa. Four samples were compared: as-drawn A1 and further-drawn A2, together with their CHPD-pressed counterparts, AP1 and AP2. X-ray diffraction confirmed the phase purity of MgB₂, with lattice parameters of (a = 3.0882) Å and (c = 3.5261) Å. SEM analysis revealed a substantial reduction in porosity and improved grain compaction following CHPD. The wire-core area decreased by 19
A first-principles study of orthorhombic CeCrO3 is carried out to investigate its structural, electronic, magnetic, elastic, and thermodynamic properties. The results confirm the stability of the orthorhombic perovskite structure. Electronic calculations indicate half-metallicity within the GGA and SCAN approximations with a magnetic moment of 8 µB. A systematic GGA + U investigation reveals a transition to a semiconducting state with increasing electron correlation, yielding a band gap of 3.02 eV, in excellent agreement with the experimental optical gap of 3.04 eV. The material exhibits a robust ferromagnetic ground state dominated by Cr moments, with contributions from Ce and O through orbital hybridization. Elastic analysis reveals a stiff, moderately ductile with a poisson’s ratio of 0.266, and anisotropic material, while thermodynamic properties confirm strong bonding and thermal stability. These findings highlight CeCrO3 as a promising candidate for spintronic, magnetoelectric, and multifunctional applications.
In the present work, pure and Mn (0.00, 0.02) doped Ni/NiO nanocomposites were synthesized via a microwave-assisted sol-gel auto-combustion method. The synthesized samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurements. Raman analysis revealed the presence of 1LO mode for pure Ni/NiO and 2LO mode for Mn-doped Ni/NiO. AFM images confirmed uniform and densely packed grains with root-mean-square (RMS) roughness values ranging from 23 to 32 nm. The 2 Θ _D ≈303–320 K). Doping significantly enhances the residual resistivity and electron-phonon scattering coefficient, consistent with stronger disorder scattering.
We report a first-principles investigation on cubic double perovskite Rb2WBr6, which exhibits an exceptional combination of structural robustness, mechanical flexibility, perfect spin polarization, high Curie temperature, and giant magnetic anisotropy-key merits urgently demanded in advanced spintronics. This compound possesses excellent thermodynamic stability confirmed by tolerance factor, negative formation energy, and cohesive energy. Mechanical evaluations demonstrate its satisfied Born-Huang stability, superior ductility, and intrinsic flexibility, enabling facile integration into flexible devices. Remarkably, Rb2WBr6 is identified as a robust half-metal with 100
Here, we introduce a high-precision Monte Carlo study examining the static critical behavior of the 4-state Potts model subjected to quenched disorder on a hexagonal lattice. The calculations are conducted for spin systems under periodic boundary conditions at spin concentrations of p = 1.0–0.80. Systems with linear sizes L in the range L = 21–180 are studied. The fourth-order Binder cumulant method is employed for determining the critical temperatures. The critical exponents β, γ, α, and v, describing magnetization, susceptibility, heat capacity, and correlation radius respectively, were determined using finite-size scaling theory for the dilution range p studied. Our findings affirm a second-order phase transition, exhibiting critical exponents consistent with the undiluted pure (p = 1.00) 2D 4-state Potts model’s universality class. For weak non-magnetic dilution (p = 0.90, 0.80), the addressed model exhibits a new set of critical exponents, defining a universality class different from the pure Potts model.
This work investigates quantum correlations in a thermally equilibrated two-qubit Heisenberg XXZ spin chain extended with Dzyaloshinskii–Moriya (DM), Kaplan–Shekhtman–Entin–Wohlman–Aharony (KSEA) interactions, and a physically motivated asymmetric exchange anisotropy ( δ ) that breaks the symmetry within the xy-plane. We derive the exact thermal density matrix and analytically evaluate two measures of non-classicality: Local Quantum Uncertainty (LQU) and Trace Distance Discord (TDD). We complement this with an analysis of concurrence as a standard entanglement measure to provide a comprehensive comparative perspective. Our results show that the DM interaction significantly enhances and thermally stabilizes both LQU and TDD. In contrast, the asymmetric anisotropy δ plays a contrary role: it consistently suppresses these quantum correlations, a behavior not reported in previous generalized models. The KSEA interaction introduces a distinct effect that slows the thermal decay of TDD. We provide a spectral explanation for this behavior by examining the energy gap structure of the Hamiltonian. The results demonstrate how the competition between different types of spin–orbit couplings—antisymmetric DM, symmetric KSEA, and the new in-plane anisotropy δ —can be used to control the robustness of quantum correlations against temperature fluctuations. We also discuss how these coupling constants can be linked to experimentally accessible regimes in strained quantum dots or cold-atom lattices.
This study using the first-principles density functional theory (DFT) calculation within the CASTEP package, we systematically investigate the structural, electronic, magnetic and optical properties of bulk, monolayer VBi and effects of external electric field and the biaxial strain to the monolayer.The bulk phase crystallizes with a lattice constant of 6.32 Å and an indirect band gap of 0.65 eV (PBE-GGA) and 1.2 eV (HSE06), which is indicative of half-metallic behaviour.The band gap of GGA is 0.59 eV, and it is 0.98 eV for HSE06 in the spin-down channel, For the monolayer, the lattice constant is 8.2 Å and the total magnetic moment is 2μ B, which is in accord with the Slater-Pauling rule (Zt = 8). The half-metallic character is maintained in the presence of biaxial strain (-6
The electronic and magnetic properties of an extended-supercell Fe@Si-doped SiC nanotube were investigated using spin-polarized density functional theory. First, the electronic structure of the pristine SiC nanotube was analyzed, revealing a direct band gap of approximately 1.67 eV, confirming its intrinsic semiconducting character with a non-magnetic ground state. Subsequently, the substitutional doping of Fe at the Si site was introduced to explore the modification of electronic and magnetic properties. The calculated band structure demonstrates that Fe incorporation significantly reduces the band gap to approximately 0.37 eV, indicating strong impurity-induced electronic states within the band gap region. The spin-polarized density of states reveals a pronounced asymmetry between spin-up and spin-down channels, confirming the emergence of magnetism in the doped nanotube. Orbital-projected density of states analysis indicates that the magnetic behavior mainly originates from the partially filled Fe-3d orbitals, which strongly hybridize with the p orbitals of neighboring Si and C atoms. Mulliken population analysis shows that the Fe dopant carries a dominant magnetic moment of 3.14 µB, while smaller induced magnetic moments appear on surrounding atoms, leading to a total magnetic moment of 4.005 µB for the supercell. Geometry optimization results confirm that the doped nanotube is structurally stable with small residual forces and negligible internal stress. The combined electronic and magnetic analyzes demonstrate that Fe substitution effectively tunes the electronic structure and induces stable spin polarization in SiC nanotubes, suggesting promising applications in spintronic and nanoelectronic devices.
Geometrically frustrated systems exhibit intriguing physical phenomena under applied magnetic fields. The rare-earth tetraboride (RB _4 , R is a magnetic rare-earth) family, a Shastry–Sutherland frustrated magnetic system, displays plateaus at fractional values of the saturation magnetization. Because of its metallic character, RB_4 could be an ideal platform for investigating the interplay between conduction electrons and fractional plateau phases. Here, we investigate the electrical transport of HoB_4 , which is a member of the RB_4 family that possesses fractional magnetization plateaus. We observe pronounced peak-like features and a violation of Kohler’s rule in the magnetoresistance associated with the complex magnetic phases. In addition, we identify a distinct hump-like anomaly in the Hall resistivity corresponding to the fractional plateau phases. We propose that the hump-like feature is most likely a manifestation of the topological Hall effect, arising from the real-space accumulation of Berry curvature due to non-coplanar spin textures. Our work provides new insights into the origin of the fractional magnetization plateaus in HoB_4 and serves as a useful reference for understanding frustrated magnetism in metallic systems.
A series of Ga1-xAlxFeO3 (x = 0, 0.2, 0.4 and 0.6) solid solutions were synthesized through the conventional solid-state reaction method to investigate the effect of Al3+ substitution on their structural, microstructural, magnetic, and dielectric properties. Room temperature X-ray diffraction (XRD) and neutron diffraction (ND) analyses confirm the formation of the non-centrosymmetric orthorhombic structure across all compositions. Detailed Rietveld refinement of both XRD and ND patterns provided quantitative insights into lattice parameters, cation distribution, and structural distortions induced by Al3+ substitution. Raman spectroscopy further corroborates the formation of the orthorhombic phase, revealing 15 Raman-active vibrational modes characteristic of GaFeO3. Scanning electron microscopy (SEM) micrographs exhibit well-defined grains and distinct grain boundaries, while progressive Al3+ substitution results in systematic grain size reduction. Low-temperature (5–300 K) dc magnetization measurements, including zero-field-cooled (ZFC) and field-cooled (FC) protocols along with magnetic hysteresis (M-H) loops, reveal a clear paramagnetic-ferrimagnetic transition (TN). Notably, TN shifts toward higher temperatures with increasing Al3+ concentration, approaching room temperature. The enhancement in magnetic transition temperature is attributed to structural distortion and modified Fe–O–Fe superexchange interactions induced by Al3+ substitution. Temperature-dependent dielectric measurements exhibit anomalies near TN, indicating significant indirect magnetoelectric coupling in all solid solutions. Overall, Al3⁺ substitution in GaFeO3 effectively modulates magnetic ordering and enhances magnetodielectric coupling, highlighting the potential of Ga1-xAlxFeO3 solid solutions for multifunctional and spintronic device applications.
Rare-earths dicarbides REC2 (RE = Ce, Pr, Nd, Sm, Gd and Dy) in CaC2-type structure are investigated through density functional theory (DFT). The understudy dicarbides are highly correlated electron systems because of the 4f orbital of RE atoms. To treat these systems, exchange correlation functional generalized gradient approximation along with Hubbard U (GGA + U) is utilized. The phonon spectra confirm the dynamic stability of these carbides and the calculated lattice parameters are found to be in closed agreement with the existing experimental data. The magnetic ground state optimization energies demonstrate that all these carbides are stable in antiferromagnetic (AFM) phase. The electron charge density plots and electronegativity difference on Pauling scale confirm the covalent between rare-earth ion (RE+ 3) and acetylide ion C2. All of these carbides’ electronic properties in the AFM phase reveal their metallic nature. The ductility of all these intermetallics is revealed by the elastic parameters. All these carbides possess intermediate Vickers’s hardness confirming their moderately hard nature. Based on the physical properties of these dicarbides like moderate hardness, high temperature strength and metallic nature it is expected that they could be considered as a suitable candidate for high temperature applications provided they are adequately shielded from atmospheric moisture.
We systematically investigated the magnetic properties of TbFeCo thin films as a function of thickness between 17 and 34 nm, with and without a Ta buffer layer, focusing on anisotropy behavior and magnetic compensation effects. Films grown on thermally oxidized SiO2/Si substrates without Ta buffer layer exhibit pronounced perpendicular magnetic anisotropy (PMA), which is attributed to strain-induced effects associated with surface roughness induced by the substrate. Across both series, the out-of-plane magnetization remains higher than the in-plane response, and the minimum saturation magnetization occurs at intermediate thicknesses, suggesting proximity to a thickness-driven magnetic compensation regime. Notably, the compensation-like minimum appears at significantly greater thicknesses than values reported for films grown on other substrates, indicating that thermally oxidized Si shifts the effective compensation thickness beyond 24 nm. These findings highlight the crucial role of substrate interface and structural morphology in tailoring the magnetic anisotropy and compensation behavior of TbFeCo thin films for spintronic applications.
The Gd3+/Dy3+ co-doping compounds of Gd(1 – x)DyxPO4 (x = 0, 0.1, and 0.2) were synthesized via chemical precipitation and solid-state reaction. The crystal structures, phase transition temperatures, maximum value of the magnetic entropy changes (−ΔSMax M), and relative cooling powers have been investigated. X-ray diffraction revealed that the samples exhibited monoclinic crystal structures with the P21/n space group. The magnetization measurements revealed that the samples underwent second-order ferromagnetic-paramagnetic transitions, and the transition temperature decreased with increasing Dy content. Under the magnetic field of 50 kOe, large −ΔSMax M values of 50.1, 43.7, and 41 J/kg K were obtained at a temperature close to the liquid helium temperature. As the Dy content increased, the RCP and TEC(2) were significantly improved. The considerable MCEs suggest that these compounds can be used in the development of low-temperature magnetic refrigeration materials.
A series of Ni and Ce co-doped magnesium ferrite nano materials with composition Mg1−xNixCeyFe2−yO4 (where y = x= 0.00, 0.025, 0.050, 0.075 and 0.1) were synthesized via a low temperature citrate gel auto combustion method. The PXRD (powder X-ray diffraction) confirmed single phase spinel structures with crystalline size in the ranges of 20.16 nm to 25.28 nm. The morphological studies and particle size distribution of the materials examined by scanning electron microscope. The samples spinel structure verified by FTIR absorption bands at both sites tetrahedral and octahedral. The optical band gap energies varied from 1.705 to 2.191 eV, with the minimum value (1.705 eV) observed for Mg0.925Ni0.075Ce0.075Fe1.925O4 indicating enhanced visible absorption. Magnetic measurements showed ferrimagnetic behaviour with saturation magnetization decreased from 15.35 to 10.42 emu/g with increasing dopant content. The photocatalytic activity was investigated through organic effluents methylene blue and acid red and the results demonstrated that Mg0.95Ni0.05Ce0.05Fe1.95O4 showed the highest degradation activity, reaching about 50
With infrared Fourier-transform spectroscopy and spectroscopic ellipsometry we investigated the in-plane reflectance of the superconducting Na _0.27 K _0.27 Rb _0.27 Fe _1.7 Se _2 single crystals with a critical temperature T_c≈ 34.3 K over a broad frequency range at temperatures of 4–300 K. The normal-state response of Na _0.27 K _0.27 Rb _0.27 Fe _1.7 Se _2 is analyzed by a Drude-Lorentz model with one Drude component. The temperature dependences of the plasma frequency, optical conductivity, scattering rate, and dc resistivity of the Drude component in the normal state are presented. We report a Fano-shaped mode at 1430 cm ^-1 indicating a coupling of the discrete mode presumably related to some electronic transition to a two-magnon continuum as well as a low-frequency broad band assigned to the acoustic magnon branch of the antiferromagnetic superstructure. These features persist in the reflectance in both the normal and superconducting states suggesting a mesoscopic coexistence of superconductivity and magnetism in Na _0.27 K _0.27 Rb _0.27 Fe _1.7 Se _2 .
