Magnetism

We report on the finite temperature staggered spin susceptibility $\chi \left(Q\right)$ as a function of the mode–mode coupling constant $y_1$ in the self-consistent renormalization theory of two-dimensional antiferromagnetic spin fluctuations with zero-point quantum fluctuations just at the quantum critical point ($y_0$ = 0). We find that the value $y_1$ = 0.1 is a criterion to classify the effect of the zero-point spin fluctuations on the temperature dependence of $\chi \left(Q\right)$ into a Curie law for weak $y_1<$ 0.1 and a Curie–Weiss type or a power law type for strong $y_1>$ 0.1. The absence of a Curie–Weiss temperature can serve as an identifying criterion for QCP ($y_0$ = 0) in systems with weak mode–mode coupling ($y_1<$ 0.1). Experimental application on the $y_1$ classification is shown to several itinerant layered antiferromagnetic systems through an analysis of nuclear spin–lattice relaxation rates. Full article

This study investigates the use of magnetoelastic sensing for vibration-based structural health monitoring (SHM) of cementitious beam specimens under intact and damaged conditions. Prismatic mortar beams with dimensions of 160 × 40 × 40 mm³ were fabricated following standardized preparation procedures and equipped with annealed amorphous ferromagnetic ribbons, Metglas 2826MB3, for nondestructive magnetoelastic vibration sensing. The specimens were tested under free-vibration conditions in a simply supported configuration, and their vibration response was measured using a detection coil and subsequently analyzed using MATLAB software. The undamaged specimen exhibited a dominant resonance frequency at 6531 Hz, which closely corresponded to the fourth bending mode predicted by Euler–Bernoulli beam theory. Controlled notch-shaped cracks with varying locations and depths were subsequently introduced to evaluate the sensitivity of the sensing system to structural damage. Experimental results showed that the frequency shift is strongly influenced by the location of damage relative to the modal nodes, with maximum sensitivity observed between nodal regions and minimal variation near the nodes. Furthermore, increasing notch-shaped crack depth produced progressively larger frequency shifts, revealing a monotonic and non-linear relationship between damage severity and dynamic response. Polynomial fitting and 3D surface analysis further highlighted the combined influence of crack location and depth on the measured frequency variation. The findings confirm that the magnetoelastic sensor is capable of accurately detecting and magnetically transmitting the vibration state and damage-induced changes in cementitious structures, demonstrating high sensitivity and strong potential for application in vibration-based structural health monitoring systems, particularly in materials characterized by strong vibration damping. Full article

We investigated the structural, magnetic, magnetocaloric, and magnetotransport properties of Ni₅₀Mn₃₅In₁₅ Heusler alloys via partial substitution of Ni with 3 at.% Bi (Ni₄₇Bi₃Mn₃₅In₁₅) and 3 at.% Si (Ni₄₇Si₃Mn₃₅In₁₅) synthesized by arc melting. X-ray diffraction confirms a predominantly L2₁ cubic structure (space group Fm-3m), while SEM/EDX analysis verifies compositional homogeneity. Temperature-dependent magnetization measurements reveal that the Bi-substituted alloy exhibits a first-order magnetostructural transition associated with the martensitic transformation, followed by a second-order magnetic phase transition from ferromagnetic to paramagnetic behavior near the Curie temperature. In contrast, the Si-substituted alloy shows a single second-order transition with negligible thermal hysteresis, indicating suppression of the martensitic phase. The Curie temperature decreases from 324 K for the parent alloy to 313 K and 286 K for the Bi- and Si-substituted alloys, respectively. A maximum magnetic entropy change of 6.0 Jkg⁻¹K⁻¹ and 4.5 Jkg⁻¹K⁻¹ is observed for the Bi- and Si-substituted alloys, respectively, under an applied magnetic field change of 50 kOe, with corresponding relative cooling power values of 303 Jkg⁻¹ and 345 Jkg⁻¹. These results demonstrate that lattice expansion (Bi) and contraction (Si) distinctly modify Mn–Mn exchange interactions, enabling tunable magnetocaloric performance in Ni–Mn–In Heusler alloys. Full article

In a previous paper, in-plane magnetoresistance results were reported on a thin strip-shaped foil sample of nanocrystalline (nc) Ni metal. These studies have now been complemented by a measurement of the temperature dependence of the resistivity as well as the field dependence of the resistivity and the Hall effect on the same sample at 3 K and 300 K in polar magnetic fields up to 140 kOe, i.e., with the magnetic field perpendicular to the strip plane. Due to the strong contribution of grain-boundary scattering in the nc state, the residual resistivity was about 11% of the room-temperature value. The polar magnetoresistance (PMR) showed similar behavior to the previously reported transverse magnetoresistance (TMR), yielding an anisotropic magnetoresistance (AMR) value in good agreement with the AMR previously deduced from the in-plane MR data. As to the Hall effect, the results for the ordinary (R_o) and the anomalous (R_s) Hall coefficient fitted rather well with the rather dispersed reported data of bulk Ni at both temperatures. However, a closer look at the R_s values for nc-Ni revealed that at 300 K it is larger and at 3 K it is smaller than the corresponding bulk Ni values obtained on samples with the same zero-field resistivity as our nc-Ni foil. These deviations may be attributed to the nanocrystalline state containing a large density of grain boundaries. Full article

I analyze the nonlinear Hamiltonian equations of motion for a one-dimensional chain of transverse magnetic nano-islands, seeking solutions for different types of static domain walls (DWs) connecting uniform static states. The system of elongated magnetic islands oriented transverse (y-direction) to the chain direction (x-direction) experiences an applied magnetic field transverse to the chain. The macro-spin model includes dipole interactions between islands, their uniaxial and easy-plane anisotropies, and Oersted energy of the applied field. DWs can form most easily between pairs of degenerate uniform states, described by their local magnetizations as oblique, y-parallel, and y-alternating. The DWs between oblique states are well described with scalar ${\phi }^4$ theory. General DW structures are found via a numerical energy relaxation scheme. At some anisotropy and field parameters, nearest-neighbor dipole interactions drive antiferromagnetic order inside the DW itself. Full article

The development of efficient and accurate methods for analyzing electromagnetic scattering by cylindrical objects has theoretical and practical relevance due to its importance in photonics, optoelectronics, antennas, and remote sensing applications. Modal methods are a category of semi-analytical solvers used in modelling electromagnetic scattering problems. Modal methods have several advantages compared to fully numerical methods, and they are very useful for problems with translational symmetry. In this paper, the interaction of electromagnetic waves with a cylinder with an impedance surface situated between two homogeneous half-spaces with different electromagnetic properties is studied. A forward model of the addressed scattering problem is presented. A theoretical formulation of the problem is deduced within a flexible and comprehensive framework that can be extended to solve other related cylindrical configurations. Furthermore, the modal solver developed within the proposed framework can be further developed to consider other forms of source excitations. Moreover, the impedance-dominant scenario has been investigated, and a convergent scheme has been derived for the special case within this regime. Full article

Rare-earth-based permanent magnets have the unique ability to create Tesla-strength magnetic fields without the need for power supplies. Moreover, Halbach showed that the fields of assemblies of magnets can be calculated analytically, because the permeability of permanent magnets is very close to unity. But that only worked in the absence of materials with a non-unity permeability, which implies that numerical tools must be employed to account, for example, for materials used to shield stray fields. Here we employ the method of images to derive analytic expressions for the magnetic field of Halbach multipoles that are enclosed in infinite-permeability shielding. Full article

In this work, the electronic, structural, and magnetic properties of Ti-, V-, Cr-, Mn-, and Ni-doped AgZnF₃ perovskites are systematically investigated using the Korringa–Kohn–Rostoker method combined with the coherent potential approximation (KKR-CPA) within the generalized gradient approximation (GGA). Transition metal dopants (Ti and V) at a concentration of 5% substituting the Zn site introduce 3d states that cross the Fermi level in the majority-spin channel, resulting in half-metallic behavior. Ferromagnetic stability is predicted for Ti-, V-, Cr-, and Mn-doped AgZnF₃ at a doping concentration of 5%. The TM-doped AgZnF₃ alloys exhibit noticeable variations in exchange splitting between the t₂g and e_g states of the TM-3d orbitals. In Ti-doped AgZnF₃, the calculated spin magnetic moments follow the expected trend based on crystal-field splitting theory. Furthermore, a clear correlation is observed between the nature of the transition metal dopant (Ti, V, Cr, Mn, and Ni) and the total magnetic moment of the system. Full article

This paper outlines a simple theoretical argument for the possibility of a quantum linear Voigt effect at low temperatures in certain media in the optical regime. An unlikely starting point for the ensuing argument arises out of a long-established hydrodynamic Lorentz field-modified classical dispersion theory whose Voigt component of the optical conductivity, when subjected to the Uncertainty Principle, results in a modified form in the quantum region. In contrast to its classical, second-order counterpart, this quantum Voigt conductivity is shown to have a (modular) linear field dependence. Full article

In this study, Nd-Fe-B magnets with different degrees of alignment were prepared by adjusting the strength of the alignment magnetic field. The mechanism of influence of alignment degree on the densification of magnets was systematically investigated. The shrinkage rates of the magnets after sintering were calculated, and the results showed that the unoriented magnets exhibited similar shrinkage in different directions, displaying isotropic shrinkage behavior. With the increase in the degree of alignment, the magnets showed significant differences in shrinkage across different directions, presenting anisotropic shrinkage characteristics. In addition, the microstructural analysis revealed that the alignment degree also exerted a certain influence on the micromorphology of the magnets. The grain size parallel to the c-axis was larger than that parallel to the a-axis, which indicates that the alignment degree plays a crucial role in the anisotropic densification of the Nd-Fe-B magnets. Full article

This paper presents a detailed parametric optimization of a spoke-type double stator and single-rotor (DSSR)-type axial flux permanent magnet (AFPM) motor based on the design of experiment (DoE) method coupled with 3D finite element analysis (FEA). Design variables are selected, and their individual effects on the output characteristics of the spoke-type DSSR AFPM motor are analyzed. The interactive effects of the design variable pairs are also investigated to understand their mutual influence on the spoke-type DSSR AFPM motor’s output characteristics. For the optimal design of the spoke-type DSSR AFPM motor, different values of each design variable are determined using Latin Hypercube Sampling (LHS) and analyzed using the 3D FEA method. Full article

This paper presents a comparative modeling and analysis of an induction furnace for melting aluminum (Al) and copper (Cu), focusing on their electromagnetic behavior and heating performance. The study employs ANSYS Maxwell software version 16.0 with the finite element method (FEM) to simulate eddy current generation, Joule heating, and current density distribution in the metallic workpieces. The effects of coil geometry, input current, and operating frequency (50–100 kHz) on heating efficiency and skin depth are investigated. Estimated heating times based on ohmic losses are provided, revealing significant differences between aluminum and copper due to their distinct electrical and thermal properties. The results demonstrate that higher frequencies concentrate heating near the surface, reducing skin depth, while copper exhibits more uniform heating than aluminum. These findings offer practical insights for optimizing induction furnace design and operation for different non-ferrous metals. Full article

We investigate a ferrimagnetic/ferroelectric bilayer in which a mixed-spin Heisenberg ferrimagnet is coupled to a three-state ferroelectric layer allowing for a nonpolar state. Using Monte Carlo simulations, we analyze how magnetic and electric single-ion anisotropies, together with interfacial magnetoelectric coupling, control phase transitions and hysteresis properties. We show that electric anisotropy, by tuning the population of nonpolar ferroelectric sites, strongly shifts the ferrimagnetic critical temperature, while magnetic anisotropy reciprocally affects the ferroelectric transition. Increasing the magnetoelectric coupling enhances both ordering temperatures and may induce a common transition. At fixed temperature, magnetic and electric hysteresis loops evolve from square to slim and nearly reversible shapes as anisotropies are varied. These results highlight the relevance of three-state ferroelectricity for describing polarization suppression and tunable magnetoelectric response in hybrid bilayers. Full article

We investigate the role of single-ion anisotropy in stabilizing higher-order skyrmion crystal phases in centrosymmetric magnets under D_3d symmetry. Using a classical spin model that incorporates both a local single-ion anisotropy arising from the two-dimensional crystal symmetry and a D_3d-type magnetic anisotropy originating from the D_3d point-group symmetry, we perform simulated annealing calculations to explore the ground-state spin configurations. We find that a skyrmion crystal with a skyrmion number of two is stabilized over a wide range of parameters of single-ion anisotropy and D_3d-type anisotropy. We also show that the skyrmion core position shifts from an interstitial site to an on-site location as the magnitude of the easy-axis single-ion anisotropy increases. Furthermore, we demonstrate that the magnetic field drives a variety of topological phase transitions depending on the sign and magnitude of the single-ion and D_3d-type anisotropies. These results provide a possible microscopic understanding of how complex topological spin textures can be stabilized in centrosymmetric D_3d magnets, suggesting that multiple phases with topological spin textures could emerge even in the absence of the Dzyaloshinskii–Moriya interaction. Full article

A magnetic vortex, characterized by curling in-plane magnetization, is generally unstable in two-dimensional (2D) ferromagnetic thin films. Here, we demonstrated that this vortex could be stable in three-dimensional (3D) pyramid-shaped Fe thin films and elucidated mechanistic origin of the stable vortex. Magnetization measurements reveal characteristic $M-H$ hysteresis loops with a pronounced bending and a gradual slope near zero magnetization, contrasting strongly with the abrupt switching seen in 2D films. By decomposing the magnetization processes on each facet in pyramid, we identify the sequence of vortex formation, stabilization, and annihilation. The key factor is the 3D geometry: non-coplanar facet junctions at the ridge lines act as structural singularities that naturally pin domain walls (DWs). These ridge lines restrict DW motion, confine local magnetic structures, and mediate inter-facet interactions, creating geometrical constraints enhancing vortex stability. Vortex formation is driven by magnetostatic energy minimization, as in 2D films. However, ridge-induced weakening of inter-facet exchange becomes the dominant factor in the 3D pyramidal structure. Overall, the interplay of shape anisotropy, magnetostatic, exchange, and Zeeman energies under 3D constraints provides a clear framework for vortex stability, offering the first mechanistic insight into stable vortices in 3D ferromagnetic films and supporting future 3D magnetic devices. Full article

This work presents a micromagnetic investigation of monolayer L1₀ FePt and FePt/Fe bilayer thin films to clarify the role of thickness, composition, and exchange coupling in their magnetic behavior. Simulations were performed using the Landau–Lifshitz–Gilbert formalism implemented in OOMMF, with realistic material parameters and geometries. For FePt monolayers, film thicknesses of 1–20 nm were examined, revealing a non-monotonic coercivity trend: the coercive field increased from 35 mT at 1 nm to 136 mT at 10 nm and decreased to 69 mT at 20 nm. This evolution indicates a transition from localized reversal to domain-wall-mediated switching once the film exceeds the exchange length (10–20 nm). Additional simulations varying Fe concentration (48–68%) through the exchange stiffness constant showed that higher Fe content strengthens magnetic coupling and increases coercivity. Bilayer systems combining a 2 nm FePt layer with Fe layers of 10 and 12 nm exhibited rectangular, saturated loops, confirming strong exchange coupling and exchange-spring behavior. The results identify 2 nm FePt as the optimal thickness for achieving full saturation, balanced coercivity, and thermal stability in FePt/Fe thin-film architectures. Full article

We theoretically investigate multiple-Q instabilities in centrosymmetric hexagonal magnets, formulated as superpositions of independent six ordering wave vectors related by sixfold rotational and mirror symmetries. By employing a spin model that incorporates biquadratic interactions and an external magnetic field, we establish a comprehensive low-temperature phase diagram hosting single-Q, double-Q, triple-Q, and sextuple-Q states, as well as skyrmion crystals with topological charges of one and two. The field evolution of the magnetization, scalar spin chirality, and finite wave-vector magnetic amplitudes reveals a hierarchical buildup of multiple-Q order, accompanied by first-order transitions between topologically distinct and trivial phases. At large biquadratic coupling, all six symmetry-related ordering wave vectors coherently participate, giving rise to two sextuple-Q states under magnetic fields and to another spontaneous sextuple-Q state even at zero field. The latter zero-field sextuple-Q state represents a fully developed sixfold interference pattern stabilized solely by the biquadratic interaction, characterized by alternating skyrmion- and antiskyrmion-like cores with vanishing uniform scalar spin chirality. These findings establish a unified framework for understanding hierarchical multiple-Q ordering and demonstrate that the interplay between bilinear and biquadratic interactions under hexagonal symmetry provides a generic route to complex noncoplanar magnetism in centrosymmetric itinerant systems. Full article