Search Results (112)

This study systematically investigates the impact of Cu²⁺ doping on the structural, magnetic, and magnetocaloric properties of Cu_xCo_1−xCr₂O₄ nanoparticles synthesized via a solution combustion method. Cu incorporation up to x = 20% induces a progressive structural transformation from a cubic spinel to a trigonal corundum phase, as confirmed by X-ray diffraction and Raman spectroscopy. The doping process also leads to increased particle size, improved crystallinity, and reduced agglomeration. Magnetic measurements reveal a transition from hard to soft ferrimagnetic behavior with increasing Cu content, accompanied by a notable rise in the Curie temperature from 97.7 K (x = 0) to 140.2 K (x = 20%). The magnetocaloric effect (MCE) is significantly enhanced at higher doping levels, with the 20% Cu-doped sample exhibiting a maximum magnetic entropy change (−ΔS_M) of 2.015 J/kg-K and a relative cooling power (RCP) of 58.87 J/kg under a 60 kOe field. Arrott plot analysis confirms that the magnetic phase transitions remain second-order in nature across all compositions. These results demonstrate that Cu doping is an effective strategy for tuning the magnetostructural response of CoCr₂O₄ nanoparticles, making them promising candidates for low-temperature magnetic refrigeration applications. Full article

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

Diluted magnetic semiconductors (DMSs) represent a significant area of interest for research and applications in spintronics. Recently, DMSs derived from BaZn₂As₂ have garnered significant interest due to the record Curie temperature (T_C) of 260 K. However, the influence of doping on their magnetic evolution and transport characteristics has not been thoroughly investigated. This study aims to fill this gap through susceptibility and magnetization measurements, electric transport analysis, and muon spin relaxation and rotation (µSR) measurements on (Ba_1−xRb_x)(Zn_1−yMn_y)₂As₂ (0.1 ≤ x, y ≤ 0.25, BRZMA). Key findings include the following: (1) BRZMA showed a maximum T_C of 138 K, much lower than (Ba,K)(Zn,Mn)₂As, because of a reduced carrier concentration. (2) A substantial electromagnetic coupling is evidenced by a negative magnetoresistance of up to 34% observed in optimally doped BRZMA. (3) A 100% static magnetic ordered volume fraction is achieved in the low-temperature region, indicating a homogeneous magnet. (4) Furthermore, a systematic and innovative methodology has been initially proposed, characterized by clear step-by-step instructions aimed at enhancing T_C, grounded in robust experimental findings. The findings presented provide valuable insights into the spin–charge interplay concerning magnetic and electronic transport properties. Furthermore, they offer clear direction for the investigation of higher T_C DMSs. 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

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 spin wave renormalization processes in two-dimensional van der Waals ferromagnetic monolayers are investigated using an established non-bosonic diagram technique based on the drone-fermion perturbation method. The aim is to evaluate the damping of the long-wavelength spin wave modes at temperatures below the Curie temperature. In addition to the multi-magnon scattering processes, which typically dominate at low temperatures, an additional mechanism is found here that becomes important at elevated temperatures. This spin disorder damping mechanism, which was mainly studied previously in bulk magnetic materials and thicker films, features a spin wave or magnon being scattered by the magnetic disorder that is present when a longitudinal spin component undergoes large thermal fluctuations. The magnetic ordering in the monolayers is stabilized by an out-of-plane single-ion or Ising-type anisotropy, which influences the damping properties. Numerical results are derived for monolayer films of the van der Waals ferromagnet Cr₂Ge₂Te₆. 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

In this study, we aimed to induce controlled structural disorder through a double substitution approach in the La_0.5Ca_0.5MnO₃ compound by investigating La_0.5−xRe_xCa_0.5−yAe_yMnO₃ compounds with x = 0.05 and 0.1 and Re = Eu, Nd, Gd, Pr, and Ae = Ba and Sr. The y values are adjusted to maintain a constant average ionic radius (<r_A> = 1.198 Å) and an unchanged Mn^3+/Mn⁴⁺ ratio. These samples were synthesized using the sol–gel method. XRD analysis confirms structural stability despite the induced disorder, showing subtle lattice distortions. Magnetic measurements reveal that introducing low disorder annihilates the charge ordered (CO) state, enhances double-exchange interactions, and influences the ferromagnetic (FM) volume fractions. Moderate disorder strengthens AFM–CO state, triggering a first–order metamagnetic transition and reducing the Curie temperature value. Magnetic field-dependent magnetization data show disorder dependent magnetic behavior and suggest the presence of the Griffiths phase for all samples, confirming the role of structural disorder in tuning magnetic phase coexistence. Pr-based samples display a considerable magnetocaloric effect near their Curie temperature. Full article

In recent years, the discovery of the two-dimensional (2D) intrinsically ferromagnetic monolayer CrI₃ has opened up promising avenues for the advancement of spintronic devices. Nevertheless, the relatively low Curie temperature poses a significant challenge for practical applications. Herein, we determine changes in the superexchange interaction of ferromagnetic coupling caused under pressure by using first-principles calculations and Monte Carlo simulations. Based on the superexchange interaction of ferromagnetic coupling, the effect of applying high pressure on the Curie temperature of monolayer CrI₃ is investigated. With a pressure coefficient of 2.0%, the Curie temperature is enhanced to 97.3 K, which is nearly double that of the monolayer CrI₃ without pressure. In addition, the direction of the easy magnetization axis changes from the out-of-plane to the in-plane one when the pressure coefficient is 1.2%. Meanwhile, the band gap of monolayer CrI₃ can be transformed from indirect to direct by applying high pressure. Our work enriches the process of modulating the magnetic and electronic properties of 2D monolayer materials. Full article

Porphyry molybdenum deposits hold significant potential for deep exploration. However, in the Dasuji molybdenum deposit, quartz porphyry, granite porphyry, and syenogranite are sporadically exposed beneath low mountains and hilly terrain, limiting the effectiveness of traditional geological methods. Consequently, geophysical techniques have become essential in this region. This study provides new magnetism and resistivity data obtained through high-precision aeromagnetic surveys and controlled-source audio-magnetotellurics (CSAMT) profiles. These results reveal concealed deep porphyries, identify deep-seated molybdenum ore bodies, and establish a porphyry-type molybdenum metallogenic model. The porphyries exhibit the lowest magnetic values (about −200 to 370 nT), suggesting that molybdenum mineralization-related granitoids have exceeded the Curie temperature and undergone an intense magnetic weakening effect. Ferromagnetic or ferromagnetic substances have transformed into paramagnetic substances. The CSAMT results indicate that the mineralized granite porphyry generally has medium to high resistivity (300 Ω·m to 500 Ω·m) and dips southward with a 60° inclination angle. Additionally, an unclosed low-resistance anomaly in the deep region of site 0 indicates promising potential for further mineral exploration and the discovery of deeper mineralized porphyries. We interpret weak magnetic anomalies and variations in resistivity as caused by high crystallization temperatures, low oxygen fugacity, and hydrothermal alteration in the context of porphyry molybdenum deposit mineralization. Full article

The investigation of the properties of Heusler compounds is an important task that will pave the way for new applications in various fields related to magnetics and thermoelectrics. This study examines the magnetic and thermoelectric properties of Fe₂CoGa Heusler compounds prepared by casting and subsequent annealing. The Fe₂CoGa Heusler compound was found to be ferromagnetic, with a large saturation magnetization of 110 emu/g and a high Curie temperature of 1011 K. The Fe₂CoGa Heusler compound was a good thermoelectric material, with a negative Seebeck coefficient of −44 μV/K, a low electrical resistivity of 0.60 μΩm, and a high-power factor of 3000 μW/mK² at room temperature. The maximum power factor of 3230 μW/mK² for the Fe₂CoGa Heusler compound was obtained at 400 K. In order to improve the magnetic and thermoelectric properties of the Fe₂CoGa Heusler compound, Fe_2-xCo_1+xGa (x = 0–1) Heusler compounds were also prepared by casting and subsequent annealing. In the Fe_2-xCo_1+xGa (x = 0–1) Heusler compounds, the saturation magnetization slightly decreased, but the Curie temperature increased with increasing Co content (x). As regards the thermoelectric properties, the electrical resistivity of the Fe_2-xCo_1+xGa (x = 0.25–1) Heusler compounds was smaller than that of the Fe₂CoGa Heusler compound. The Seebeck coefficient and power factor of the Fe_1.75Co_1.25Ga Heusler compound were more significant than those of the Fe₂CoGa Heusler compound. An increase in the Co content of the Fe₂CoGa Heusler compound did not improve the saturation magnetization but improved the Curie temperature and thermoelectric properties of the Fe₂CoGa Heusler compound. The Fe_1.75Co_1.25Ga Heusler compound exhibited a high-power factor value of over 4000 μW/mK², which was comparable to that of the Bi₂Te₃ compound. Full article

In the field of piezoelectric applications, perovskite-based multifunctional composite ceramics are widely explored. The morphotropic phase boundary (MPB) regions, where dual structural phases coexist, play a crucial role in boosting the ferroelectric and piezoelectric properties significantly. Herein, MPB-region-existent 0.7BiFeO₃-0.3BaTiO₃ (BFBT) composite ceramic is investigated under the influence of wt%Sn-ion incorporation at the lattice sites of the BFBT. Specifically, the ceramic composition BFBT:0.2Sn has demonstrated excellent remnant polarization (P_r ~ 22.68 µC/cm²), an impressive piezoelectric coefficient (d₃₃ ~ 211 pC/N), stable impedance of 1.07 × 10⁷ Ω, a Curie temperature of 435 °C and low dielectric loss (tanδ) of <0.5. Moreover, the BFBT:0.2Sn ceramic has also maintained a stable d₃₃ of ~150 pC/N and resistivity of ~10² Ω even at a temperature of 400 °C. Such outcomes confirm the ability and potential of the BFBT:0.2Sn ceramic composition for high-temperature piezoelectric applications. Full article