Search Results (163)

Perovskite manganites (AMnO₃) and perovskite-like manganites (A’_1−xA_xMnO₃) are complex oxide materials that have attracted significant attention from the scientific community in recent years due to their structural flexibility, mixed-valence state, tunable electronic configuration, and multifunctional properties. This review systematically analyzes the synthesis methods, structural classification, and physicochemical characterization of perovskite manganites, as well as their magnetic, optical, electrical, dielectric, and catalytic properties. The influence of solid-state reactions, sol–gel, Pechini, hydrothermal, co-precipitation, microwave, and other mild chemical approaches on phase purity, morphology, particle size, and oxygen stoichiometry was examined. The structural diversity of perovskite and perovskite-like manganites, including simple ABO₃, double perovskites, multilayer, and low-dimensional systems, was characterized in relation to their functional properties. The review discussed the capabilities of methods for synthesizing and analyzing morphological properties, demonstrating the role of doping, cation substitution, oxygen vacancies, and Jahn–Teller distortions in controlling material properties. Prospects for the application of perovskite manganites in spintronics, magnetocaloric cooling, photocatalysis, gas-sensing devices, and energy conversion and storage systems were analyzed. This review highlights the structure–property–application relationship in perovskite manganites. Full article

The magnetic properties of Dy₆MnBi₂ and Dy₆FeBi₂ intermetallic compounds have been investigated within the framework of density functional theory. These materials are attracting considerable attention due to their potential in magnetic refrigeration applications, as they exhibit a pronounced magnetocaloric effect. In the present work, we compute the equation of state, electronic density of states, and magnetic moments, and compare the results with available experimental data. The calculated quantities are found to be in good agreement with the experimental findings, thereby supporting once again the reliability of DFT as a theoretical framework for exploring the magnetic behavior of ternary intermetallic compounds. Full article

Gd(III)-Gd(III) exchange interactions are central to a number of applications, such as the magnetocaloric effect or single molecule magnetism. Broken-symmetry density functional theory is the most widely used computational technique for these calculations, yet no comprehensive benchmark has been established. Here, we present the computational analysis of 27 binuclear Gd(III) compounds in comparison to experimental data and propose a best-practice workflow. We encourage the explicit treatment of scalar relativistic effects and the use of a combination of hybrid functionals with different amounts of exact exchange. Furthermore, we investigated this testbed for structure-property relationships and demonstrated the use of the recommended methodology on two tetranuclear Gd(III) clusters. 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 this paper, a ternary Tb₆₅Co₂₅Ni₁₀ amorphous tape was successfully prepared, and the glass forming ability (GFA), magnetic properties, and magnetocaloric characteristics of the amorphous tape were studied in detail. The values of the reduced glass transition temperature T_rg, parameter γ and critical section thickness Z_c indicate the good GFA of the Tb₆₅Co₂₅Ni₁₀ amorphous tape. The Tb₆₅Co₂₅Ni₁₀ amorphous tape exhibits spin-glass-like behavior, with a Curie temperature of 83 K and a spin-freezing temperature (T_f) of 73 K, and a large coercivity below T_f. The spin-glass-like behavior significantly deteriorates the magnetic entropy change (−∆S_m) of the Tb₆₅Co₂₅Ni₁₀ amorphous tape at low temperatures, resulting in the deviation of magnetic entropy change behavior from the predicted results. However, the Tb₆₅Co₂₅Ni₁₀ amorphous tape still shows an excellent magnetocaloric effect (the peak value of −∆S_m of 9.46 J kg⁻¹ K⁻¹ and the refrigeration capacity of 569.5 J kg⁻¹ under 5 T, both of which are higher than those of most other heavy rare earth-based amorphous alloys), indicating the great application potential in the field of magnetic refrigeration for the amorphous tape. Full article

Four perovskite manganite samples, La_0.80Ag_0.20MnO₃ (LA), La_0.78Eu_0.02Ag_0.20MnO₃ (LEA), La_0.80Pb_0.05Ag_0.15MnO₃ (LPA), and La_0.77Eu_0.03Pb_0.05Ag_0.15MnO₃ (LEPA), were prepared by the Pechini sol–gel method. The samples were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and a magnetic property measurement system. A systematic investigation was conducted into the individual effects of Eu and Pb doping, as well as their co-doping, on the microstructural, magnetic and magnetocaloric properties of the materials. The results show that all samples are mainly composed of a rhombohedral perovskite phase with the $\mathrm{R}\overline{3}\mathrm{c}$ space group, accompanied by a trace amount of Ag. Addition of Eu³⁺ and Pb²⁺ induces lattice contraction and expansion, respectively. Under the same processing conditions, the average crystallite and particle sizes of the LEA sample (45.3 nm and 0.18 μm) are smaller than those of the other three samples (69.6~80.6 nm and 0.38~0.44 μm), indicating that the introduction of Eu alone suppresses crystallization ability, which can be avoided through Eu/Pb co-doping. All samples undergo a second-order ferromagnetic–paramagnetic transition, and the Curie temperature T_C shifts to either lower or higher temperatures upon the introduction of Eu or Pb alone (from 310.8 K to 298.0 K or 318.0 K, respectively), which is attributed to the variation of the Mn³⁺/Mn⁴⁺ double-exchange (DE) interaction resulting from the ionic size mismatch and lattice distortion. In the LPA sample, an additional contribution arises from the altered Mn³⁺/Mn⁴⁺ ratio and enhanced DE interaction caused by the substitution of Pb²⁺ for Ag⁺. By modifying the Eu/Pb ratio, the T_C of the LEPA sample was tuned to 299.3 K, and its maximum magnetic entropy change was enhanced to 3.90 J·kg⁻¹·K⁻¹ ($∆$H = 2 T). These results indicate that multicomponent synergistic regulation can improve the magnetocaloric performance of La-based perovskite manganites, providing a useful strategy for the development of room-temperature magnetic refrigeration materials. Full article

Fe₂P compounds have recently attracted significant attention due to their large anisotropy and magnetization, making them promising candidates as hard magnetic materials. However, their relatively low Curie temperature limits practical applications. Previous studies have shown that substituting Si for P or Co for Fe increases the Curie temperature; however, Si substitution induces a hexagonal to orthorhombic structural transformation, while Co substitution reduces saturation magnetization. This work examines the evolution of the crystal structure and magnetic properties upon B substitutions in Fe_1.95P_0.8−xSi_0.2B_x compounds close to the hexagonal/orthorhombic transformation. We show that B can increase the Curie temperature up to 675 K and the saturation magnetization to 139 A·m²·kg⁻¹, while preserving the hexagonal structure beyond the limit allowed by Si substitutions only. X-ray diffraction of magnetically aligned powders confirms a uniaxial easy axis along the c axis and significant room-temperature magnetocrystalline anisotropy. The optimization of the intrinsic magnetic properties based on only metalloid substitutions paves the way for further development of this material family as rare-earth-free permanent magnets. Full article

Magnetic and structural transitions can interact significantly, leading to an enhanced magnetocaloric effect (MCE), also known as the giant or colossal effect. In this study, we investigate how subtle microstructural changes impact the magnetocaloric behavior of a MnCoGeB_0.02 alloy fabricated via suction casting. We obtained conical samples and analyzed them to understand their structure and magnetic properties. X-ray diffraction patterns revealed a coexistence of a metastable high-temperature hexagonal phase and a stable low-temperature orthorhombic phase in different regions of each cone. The presence and proportion of these phases determine the degree of magneto-structural coupling, which in turn influences the MCE. The magnetic entropy change (|ΔS_Peak|) varied notably among the samples, ranging from 12.3 to 6 Jkg⁻¹K⁻¹ under a magnetic field change of Δµ₀H = 5.0 T. These findings demonstrate that even minor microstructural changes caused by differences in solidification during suction casting can lead to noticeable variations in magnetocaloric performance. Understanding and controlling these microstructural details is vital for optimizing the functional behavior of MnCoGe-based materials. Full article

In this work, La_0.70Ca_0.25Sr_0.05MnO₃ perovskite nanoparticles were produced in large amounts (in a single batch) and were embedded into filaments for 3D printing alongside carbon fibers. The produced materials showed room-temperature magnetocaloric effects proportional to the quantity of encapsulated nanoparticles. Moreover, the thermal properties of 3D-printed pellets (produced using the composite filaments) were also analyzed and compared to standard filaments. Full article

In the present work, we selected an amorphous Nd₆₀Ni₄₀ alloy as a basic alloy and added Er with a higher effective magnetic moment and de Gennes factor to replace Nd for the purpose of improving the magnetocaloric performance of the Nd₆₀Ni₄₀ amorphous alloy. The formability, magnetization, and magnetocaloric behaviors of the Nd_60-xEr_xNi₄₀ (x = 5, 10, 15, 20) amorphous alloys were studied. It was found that Er substitution generally improved the glass formability, but simultaneously decreased the Curie temperature, coercivity, and magnetic entropy change peak of the basic alloy. The mechanism for these unexpected results was investigated, and it was supposed that the decreased Curie temperature and the deteriorated magnetocaloric properties may have resulted from the antiferromagnetic coupling between the Nd and Er atoms. Full article

To enhance the wide-temperature-range magnetocaloric performance of (Mn,Fe)₂(P,Si) alloys, the effects of Mg-Co co-doping on their structural and magnetocaloric properties were systematically investigated. Mn_1.05−yCo_yFe_0.9P_0.5Si_0.48Mg_0.02 alloys were prepared by the arc melting method. The results show that Mg-Co co-doping can tune the lattice parameters and ferromagnetic coupling between Mn and Fe atoms. The Mn_1.03Co_0.02Fe_0.9P_0.5Si_0.48Mg_0.02 alloy exhibited an effective refrigeration capacity of 425.4 J·kg⁻¹ and an effective working temperature span of 52 K. During the temperature-induced ferromagnetic transition, coupling between the magnetic moment of Fe-Si layers and the crystal lattice drives a magnetoelastic transition, leading to a giant magnetocaloric effect. The Mg-Co co-doping strategy effectively tunes the crystal structure and local electron density distribution of the Fe-Si layer, thereby influencing the total magnetic moment and magnetothermal properties of the alloys. Full article

High-entropy alloys (HEAs), as a novel class of materials, have attracted widespread attention in the field of materials science due to their unique multi-element high-concentration mixing design. Recent research has found that this alloy mixing strategy not only exhibits excellent performance in structural properties but also shows potential in functional materials. This review summarizes the progress of research on HEAs in the magnetocaloric effect (MCE) area, first introducing the basic principles of MCE and the related concepts of HEAs. It then summarizes the research progress of rare-earth HEAs, non-rare-earth HEAs, and rare-earth-transition metal composite HEAs in MCE. Finally, this review outlines future research directions for HEAs in the MCE field, laying the groundwork for further applications of HEAs in the magnetocaloric field. Full article

Co(NH₄)₂(SO₄)₂·6H₂O single crystal was grown via slow solvent evaporation at room temperature. The magnetic and magnetocaloric properties were investigated. The results show that Co(NH₄)₂(SO₄)₂·6H₂O exhibits paramagnetic behavior across 2–300 K. The maximum magnetic entropy change (−ΔS_M) of 13.90 J kg⁻¹ K⁻¹ under conditions of 2 K and μ₀ΔH = 5 T approaches the theoretical value of 14.58 J kg⁻¹ K⁻¹. In addition, the variation of −ΔS_M with temperature is relatively flat, suggesting a wide working temperature range for magnetic refrigeration, which provides the possibility for the application of Co²⁺-based compounds in the field of low-temperature magnetic refrigeration. Full article

Gd₄Co₃ is a promising magnetocaloric material with a high magnetic entropy value. However, it undergoes a first-order magnetic transition, which hinders practical applications. Hence, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) were studied to obtain high magnetic entropy values and a second-order magnetic transition. To investigate the effects of Ge addition on the thermal stability, magnetocaloric properties, and critical behavior of Gd₄Co₃-based alloys, (Gd₄Co₃)_100−xGe_x (x = 5, 10, 15) melt spun ribbons were prepared. Phase analysis showed these alloys are mainly amorphous, with a minority nanocrystalline phase. All alloys undergo a second-order ferromagnetic-to-paramagnetic transition. The Curie temperature (T_C) increases linearly from 211 K (x = 5) to 217 K (x = 15) with increasing Ge content. Under a magnetic field variation of 5 T, the alloys with x = 5, 10, and 15 exhibit peak magnetic entropy change (−ΔS_M) values of 7.15, 6.83, and 6.71 J/(kg·K), respectively, along with considerable refrigerant capacity (RC) in the range of 435–458 J/kg. These excellent magnetocaloric properties collectively demonstrate their great potential for magnetic refrigeration applications. Critical behavior analysis revealed critical exponents broadly consistent with mean-field theory (MFT, β = 0.5, γ = 1.0, δ = 3.0), indicating nanocrystals in the amorphous matrix induce long-range magnetic interactions. Full article

Intermetallic NiMn-based Heusler alloys (HAs) have garnered considerable attention due to their multifunctionality and applications in various fields, including sensors, actuation, refrigeration, and waste heat harvesters. Among the NiMn-based alloys, Ni-Mn-Sn alloys have gained considerable attention since their structural and magnetic transformations were discovered. Many studies have been conducted with various compositions and shapes to investigate the physical properties of Ni-Mn-Sn alloys, which offer several advantages, including non-toxicity, low cost, and abundant constituents. The Co-doping effect on the physical properties of Ni-Mn-Sn alloys has been widely reported. This doping can rectify the ternary Ni-Mn-Sn Heusler compound’s brittleness by crystallizing a disordered face-centered cubic (fcc) γ-phase. In this study, a polycrystalline Ni₄₂Mn₄₆CoSn₁₁ Heusler alloy was prepared by high-frequency fusion (HF), using a Lin Therm 600 device, from pure Ni, Mn, Sn, and Co elements with appropriate proportions. X-ray diffraction, scanning electron microscopy, and magnetic magnetometry devices were used to study the structural, microstructural, and magnetic properties. The XRD results revealed the coexistence of a disordered 7 M martensite phase (~88%) and a disordered cubic solid solution γ-phase (~12%). The alloy underwent a second-order ferromagnetic-to-paramagnetic phase transition at a Curie temperature of 350 K. Landau and Hamad’s theoretical models were used to plot the magnetic entropy change. The magnetocaloric properties (the maximum entropy change value, ΔS_M, the full width at half maximum of the entropy change curve, δT_FWHM, the relative cooling power, RCP, and the heat capacity, ΔC_P,H) were calculated using isothermal magnetization curves with the phenomenological model of Hamad. Full article