Search Results (201)

Metallic magnetic materials are extensively used to mitigate electromagnetic interference due to their high Curie temperatures and permeability. However, their high permittivity often hinders impedance-matching effectiveness, limiting their utility. In this study, amorphous cobalt–iron (Co_100−xFe_x) alloy nanoparticles with relatively low permittivity were synthesized using a simple aqueous reduction method at room temperature. The effect of atomic ratio variation on the microwave absorption properties of these nanoparticles was investigated across 2–18 GHz. The amorphous Co_100−xFe_x nanoparticles exhibited excellent electromagnetic wave absorption performance, achieving an effective absorption bandwidth of 5.6 GHz, a matching thickness of 2.60 mm, and a reflection loss of −42 dB. Full article

The (1−x)Ba_0.96Ca_0.04TiO₃-xBa(Mg_1/3Nb_2/3)O₃ (x = 0–0.20) lead-free ceramics were prepared through the chemical-furnace-assisted combustion synthesis (abbreviated as CFACS). The phase structure, microstructure, dielectric, and piezoelectric properties were systematically investigated. Phase analysis revealed the coexistence of orthorhombic and tetragonal phases in the vicinity of x = 0.07. More importantly, the composition with x = 0.07 exhibited optimal overall electrical properties, including a high piezoelectric coefficient (d₃₃) of 495 pC/N, the planar electromechanical coupling factor (K_p) of 41.9%, and the Curie temperature (T_c) of 123.7 °C. In addition, the average grain size was observed to progressively decrease with increasing x. Full article

This review article provides an in-depth analysis of recent advancements in the fabrication, structural characterization, and magnetic properties of Heusler alloy glass-coated microwires, focusing on Co₂FeSi alloys. These microwires exhibit unique thermal stability, high Curie temperatures, and tunable magnetic properties, making them suitable for a wide range of applications in spintronics, magnetic sensing, and biomedical engineering. The review emphasizes the influence of geometric parameters, annealing conditions, and compositional variations on the microstructure and magnetic behavior of these materials. Detailed discussions on the Taylor–Ulitovsky fabrication technique, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) provide insights into the structural properties of the microwires. The magnetic properties, including room-temperature behavior, temperature dependence, and the effects of annealing, are thoroughly examined. The potential applications of these microwires in advanced spintronic devices, magnetic sensors, and biomedical technologies are explored. The review concludes with future research directions, highlighting the potential for further advancements in the field of Heusler alloy microwires. Full article

Novel diluted magnetic semiconductors derived from BaZn₂As₂ are of considerable importance owing to their elevated Curie temperature of 260 K, the diversity of magnetic states they exhibit, and their prospective applications in multilayer heterojunctions. However, the transition from the intrinsic semiconductor BaZn₂As₂ (BZA) to its doped compounds has not been extensively explored, especially in relation to the significant intermediate compound Ba(Zn,Mn)₂As₂ (BZMA). This study aims to address this gap by performing susceptibility and magnetization measurements, in addition to electronic transport analyses, on these compounds in their single crystal form. Key findings include the following: (1) carriers can significantly modulate the magnetism, transitioning from a non-magnetic BZA to a weak magnetic BZMA, and subsequently to a hard ferromagnet (Ba,K)(Zn,Mn)₂As₂ with potassium (K) doping to BZMA; (2) two distinct sets of metal-insulator transitions were identified, which can be elucidated by the involvement of carriers and the emergence of various magnetic states, respectively; and (3) BZMA exhibits colossal negative magnetoresistance, and by lanthanum (La) doping, a potential n-type (Ba,La)(Zn,Mn)₂As₂ single crystal was synthesized, demonstrating promising prospects for p-n junction applications. This study enhances our understanding of the magnetic interactions and evolutions among these compounds, particularly in the low-doping regime, thereby providing a comprehensive physical framework that complements previous findings related to the high-doping region. Full article

Permanent magnetic materials are essential for technological applications, with the majority of available magnets being either ferrites or materials composed of critical rare-earth elements, such as well-known Nd₂Fe₁₄B. The binary Fe₂P material emerges as a promising candidate to address the performance gap, despite its relatively low Curie temperature $T_C$ of 214 K. In this study, density functional theory was employed to investigate the effect of Si and Co substitution on the magnetic moments, magnetocrystalline anisotropy energy (MAE) and Curie temperature in ${\mathrm{Fe}}_{2-y}$Co_yP_1−xSi_x compounds. Our findings indicate that Si substitution enhances magnetic moments due to the increase in 3f-3f and 3f-3g interaction energies, which also contribute to higher $T_C$ values. Conversely, Co substitution leads to a reduction in magnetic moments, attributable to the inherently lower magnetic moments of Co. In all examined cases of different Si concentrations, such as hexagonally structured ${\mathrm{Fe}}_{2-y}$Co_yP, ${\mathrm{Fe}}_{2-y}$Co_yP_0.92Si_0.08 and ${\mathrm{Fe}}_{2-y}$Co_yP_0.84Si_0.16, Co substitution increases the Curie temperatures by augmenting 3g-3g exchange interaction energies. Both Si and Co substitutions decrease the magnetocrystalline anisotropy energy, resulting in the loss of the easy magnetization direction at higher Co contents. However, higher Si concentrations appear to confer resilience against the loss. In summary, Si and Co substitutions effectively modify the investigated magnetic properties. Nonetheless, to preserve a high MAE, the extent of substitution should be optimized. Full article

Electrocaloric materials, which exhibit adiabatic temperature change under an applied electric field, are promising for solid-state cooling technologies. In this study, the electrocaloric response of lead-free Ba_xCa_1−xZr_yTi_1−yO₃ (BCZT) ceramics was modeled to investigate the effects of composition, processing, and measurement conditions on performance. A high-accuracy XGBoost regression model (R² = 0.99, MAE = 0.02 °C) was developed using a dataset of 2188 literature-derived data points to predict and design the electrocaloric response of BCZT ceramics. The feature space incorporated compositional ratios, processing parameters, measurement settings, and atomic-level Magpie descriptors, along with Curie temperature to account for phase-transition behavior. Feature importance analysis revealed that electric field, measurement temperature, and proximity to the Curie point are the most critical factors influencing ΔT_EC. Bayesian optimization was applied to navigate the design space and identify performance maxima under unconstrained and realistic constraints, offering valuable insights into the nonlinear interactions governing electrocaloric performance. Under room temperature and moderate-field conditions (24 °C, 40 kV/cm), the optimized ΔT_EC achieved a value of 1.03 °C for Ba_0.85Ca_0.15Zr_0.40Ti_0.60, to be processed at 1090 °C for 3 h during calcination, 1300 °C for 2 h during sintering. By integrating experimental insight with machine learning and optimization, this study offers a refined, interpretable framework for accelerating the design of high-performance electrocaloric ceramics while reducing the experimental workload. Full article

This paper investigates the impact of sintering temperature on oxygen vacancy concentration and its subsequent effect on the microstructure and electrical properties of $B{i}_{4}T{i}_3{O}_{12}$ (BIT) ceramics. To further clarify these effects, VASP software was employed to simulate BIT ceramics with varying oxygen vacancy concentrations.The experimental results demonstrate that sintering temperature significantly influences the oxygen vacancy concentration. At the optimal sintering temperature of 1080 °C, the BIT ceramics exhibit a balanced microstructure with a grain size of 4.16 μm, the lowest measured oxygen vacancy concentration of 18.44%, and a piezoelectric coefficient ($d_{33}$) of 9.8 pC/N. Additionally, the dielectric loss ($tan\delta$) remains below 0.2 at 500 °C, indicating excellent thermal stability. VASP-based simulations reveal that increasing the oxygen vacancy concentration from 18.56% to 44.55% results in a significant collapse of the band gap (from 2.8 eV → 1.0 eV) and a transition in conductivity type from p-type to n-type. This shift induces a leakage current-dominated threshold effect, leading to a decrease in piezoelectric properties ($d_{33}$ reduced from 9.8 to 6.9 pC/N). Atomic-scale density of states (DOS) analyses indicate that the delocalization of $T{i}^{3+}$ and the weakening of Bi–O hybridization collectively induce lattice distortion and ferroelectric inconsistency. These changes are correlated with an increase in dielectric loss and a slight reduction in Curie temperature (from 620 °C → 618 °C). In conclusion, this study comprehensively elucidates the influence of oxygen vacancy concentration on the microstructure and electrical properties of BIT ceramics. The findings provide a theoretical foundation and practical insights for designing high-performance piezoelectric ceramics. Full article

Thulium iron garnet (Tm₃Fe₅O₁₂, TmIG) is a promising material for next-generation spintronic and quantum technologies owing to its high Curie temperature and strong perpendicular magnetic anisotropy. However, conventional magnetometry techniques are limited by insufficient spatial resolution and sensitivity to probe local magnetic phase transitions and critical spin dynamics in thin films. In this study, we present the first quantitative investigation of local magnetic field fluctuations near the Curie temperature in TmIG thin films using nitrogen-vacancy (NV) center-based quantum sensing. By integrating optically detected magnetic resonance (ODMR) and NV spin relaxometry (T₁ measurements) with macroscopic techniques such as SQUID magnetometry and Hall effect measurements, we systematically characterize both the static magnetization and dynamic spin fluctuations across the magnetic phase transition. Our results reveal a pronounced enhancement in NV spin relaxation rates near 360 K, providing direct evidence of critical spin fluctuations at the nanoscale. This work highlights the unique advantages of NV quantum sensors for investigating dynamic critical phenomena in complex magnetic systems and establishes a versatile, multimodal framework for studying local phase transition kinetics in high-temperature magnetic insulators. Full article

This study explores the crystal structure, microstructure and magnetic phase evolution of the AlCoCrFeNi high-entropy alloy (HEA), highlighting its potential for applications requiring tailored magnetic properties across diverse temperatures. Electron microscopy and X-ray diffraction revealed that the as-cast alloy’s microstructure comprises equiaxed grains with branching dendrites, showing compositional variations between interdendritic regions enriched in Al and Ni. Temperature-induced phase transformations were observed above room temperature, transitioning from body centered cubic (BCC) phases (A2 and B2) to a predominant FCC phase at higher temperatures, followed by recrystallization of the A2 phase upon cooling. Magnetization measurements showed a drop near 380 K, suggesting the Curie temperature of BCC phases, a peak at 830 K attributed to optimal magnetic alignment in the FCC phase, and a sharp decline at 950 K marking the transition to a paramagnetic state. Magnetic moment calculations provided insights into magnetic alignment dynamics, while low-temperature analysis highlighted the alloy’s magnetically soft nature, dominated by ferromagnetic contributions from the A2 phase. These findings underscore the strong interdependence of microstructural features and magnetic behavior, offering a foundation for optimizing HEAs for temperature-sensitive scientific and industrial applications. Full article

The Curie temperature (Tc) of LaMnO₃-based perovskites is one of the most important properties associated with their magnetic and spintronic applications. The search for new perovskites with even higher Tc is a challenging problem in material design. Through the systematic optimization of support vector regression (SVR) architecture, we establish a predictive framework for determining the Curie temperature (Tc) of doped LaMnO₃ perovskites, leveraging fundamental atomic descriptors. The correlation coefficient (R) between the predicted and experimental Curie temperatures demonstrated high values of 0.9111 when evaluated through the leave-one-out cross-validation (LOOCV) approach, while maintaining a robust correlation of 0.8385 on the independent test set. The subsequent high-throughput screening of perovskite compounds exhibiting higher Curie temperatures was implemented via our online computation platform for materials data mining (OCPMDM), enabling the rapid identification of candidate materials through systematic screening protocols. The findings demonstrate that machine learning exhibits significant efficacy and cost-effectiveness in identifying lanthanum manganite perovskites with elevated Tc, as validated through comparative computational and empirical analyses. Furthermore, a web-based computational infrastructure is implemented for the global dissemination of the predictive framework, enabling the open-access deployment of the validated machine learning model. Full article

A very fundamental property of both weakly and strongly interacting materials is the nature of their magnetic response. In this work, we detail the growth of crystals of the quasicrystal approximant Fe₄Al₁₃ with an Al flux solvent method. We characterize our samples using electrical transport and heat capacity, yielding results consistent with a simple non-magnetic metal. However, magnetization measurements portray an extremely unusual response for a dilute paramagnet and do not exhibit the characteristic Curie behavior expected for a weakly interacting material at high temperature. Electronic structure calculations confirm metallic behavior but also indicate that each isolated band near the Fermi energy hosts non-trivial topologies, including strong, weak, and nodal components, with resultant topological surface states distinguishable from bulk states on the (001) surface. With half-filled flat bands apparent in the calculation, but an absence of long-range magnetic order, the unusual quasi-paramagnetic response suggests the dilute paramagnetic behavior in this quasicrystal approximant is surprising and may serve as a test of the fundamental assumptions that are taken for granted for the magnetic response of weakly interacting systems. Full article

The investigation of novel diluted magnetic semiconductors (DMSs) provides a promising platform for studying magnetism and transport characteristics, with significant implications for spintronics. DMSs based on BaZn₂As₂ are particularly noteworthy due to their high Curie temperature (T_C) of 260 K, diverse magnetic states, and potential for multilayer heterojunctions. This study investigates the magnetic evolution of carrier doping and spin dynamics in the asperomagnet (Ba,Na)(Zn,Mn)₂As₂, utilizing a combination of magnetization measurements, ac susceptibility, and muon spin rotation (µSR). Key findings include the following: (1) lower transition temperatures and coercive forces in (Ba,Na)(Zn,Mn)₂As₂ compared to the ferromagnet (Ba,K)(Zn,Mn)₂As₂; (2) a dynamic fluctuation peak around the transition temperature observed in both the ac susceptibility and longitudinal field (LF) µSR; and (3) the coexistence of static and dynamic states at low temperatures, exhibiting spin-glass-like characteristics. This study, to the best of our knowledge, may represent the first investigation of asperomagnetic order utilizing µSR techniques. It enhances the understanding of magnetic interactions in BaZn₂As₂-based systems and provides valuable insights into the exploration of high T_C DMSs. Full article

The newly discovered 2D spin-gapless magnetic materials, which provide new opportunities for combining spin polarization and the quantum anomalous Hall effect, provide a new method for the design and application of memory and nanoscale devices. However, a low Curie temperature (T_C) is a common limitation in most 2D ferromagnetic materials, and research on the topological properties of nontrivial 2D spin-gapless materials is still limited. We predict a novel spin-gapless semiconductor of monolayer h-VN, which has a high Curie temperature (~543 K), 100% spin polarization, and nontrivial topological properties. A nontrivial band gap is opened in the spin-gapless state when considering the spin–orbit coupling (SOC); it can increase with the intensity of spin–orbit coupling and the band gap increases linearly with SOC. By calculating the Chern number and edge states, we find that when the SOC strength is less than 250%, the monolayer h-VN is a quantum anomalous Hall insulator with a Chern number C = 1. In addition, the monolayer h-VN still belongs to the quantum anomalous Hall insulators with its tensile strain. Interestingly, the quantum anomalous Hall effect with a non-zero Chern number can be maintained when using h-BN as the substrate, making the designed structure more suitable for experimental implementation. Our results provide an ideal candidate material for achieving the QAHE at a high Curie temperature. Full article

Layered chalcogenides are interesting from the point of view of the formation of two-dimensional magnetic systems for relevant applications in spintronics. High-spin Mn²⁺ or Fe³⁺ cations with five unpaired electrons are promising in the search for compounds with interesting magnetic properties. In this study, a new layered modification of the Mn₂In₂Se₅ compound from the A₂B₂X₅ family (“225”) was synthesized and investigated. A phase transition to the polymorph with primitive trigonal lattice was recorded at a temperature of 711 °C, which was confirmed by simultaneous thermal analysis, X-ray powder diffraction at elevated temperatures, and sample annealing and quenching. The stability of Mn₂In₂Se₅ in air at high temperatures was investigated by thermal gravimetric analysis and powder X-ray diffraction. The new polymorph of Mn₂In₂Se₅ crystallizes in the Mg₂Al₂Se₅ structure type, as revealed by the Rietveld refinement against powder X-ray diffraction data. The crystal structure can be viewed as a close-packing of Se anions, in which indium and manganese cations are enclosed inside tetrahedral and octahedral voids, respectively, according to the A_MnB_InCB_InC_MnA… sequence. Magnetization measurements reveal an antiferromagnetic-like transition at a temperature of 6.3 K. The same magnetic properties are reported in the literature for the low-temperature R-centered trigonal polymorph. An approximation by the modified Curie–Weiss law yields a significant ratio of |θ|/T_N = 28, which indicates strong magnetic frustration. Full article

A site-ordered quadruple perovskites, AA′₃B₄O₁₂, can have 3d transition metals at A′ and B sites, and show complex magnetic interactions and behavior. Additional complexity appears when B site-ordered arrangements are realized in AA′₃B₂B′₂O₁₂. In this work, A site-ordered quadruple perovskites, RMn₃Ni₂Mn₂O₁₂ with R = Bi, Ce, and Ho, were prepared by a high-pressure, high-temperature method at about 6 GPa and about 1500 K. The R = Bi and Ce samples were found to crystallize in space group Im-3 with a disordered distribution of Ni²⁺ and Mn⁴⁺ cations in one B site. On the other hand, the R = Ho sample crystallized in space group Pn-3 and showed partial ordering of Ni²⁺ and Mn⁴⁺ cations between two B sites. The structural data (and bond valence sums) suggest that cerium has the oxidation state +3, which is unusual for such perovskites. Magnetic properties were investigated by magnetic susceptibility and specific heat measurements, which showed the presence of one magnetic transition near 36 K for R = Bi; there was evidence for the presence of two magnetic transitions near 27 K and 33 K for R = Ce, and near 10 K and 36 K for R = Ho. Curie–Weiss parameters were estimated for all samples from high-temperature magnetic measurements up to 750 K. The total effective magnetic moment for R = Ce also suggests the presence of Ce³⁺. A magnetic field of 90 kOe had the largest effect on the specific heat of the R = Ho sample, and almost no effects on the specific heat of the R = Bi sample. Full article