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Rare-earth transition metal-based double perovskite ceramics E2TMO6 (where E = rare-earth metals, T = transition metals, and M = metal) have received impressive attention lately for cryogenic applications as a result of their intrinsic physical features such as multiferroicity, dielectric features, and adjustable magnetic transition temperature. However, determination and enhancement of magnetic transition temperature of E2TMO6 ceramic are subject to experimental procedures and processes with a significant degree of difficulties and cumbersomeness. This work proposes an extreme learning machine (ELM)-based intelligent method of determining magnetic transition temperature of E2TMO6 ceramics with activation function sigmoid (SM) and sine (SE) at varying magnetic field. The outcomes of the SE-ELM and SM-ELM models were compared with genetically optimized support vector regression (GEN-SVR) predictive models using RMSE, CC, and MAE metrics. Using the testing samples of E2TMO6 ceramics, SE-ELM predictive model outperforms GEN-SVR with a superiority of 6.3% (using RMSE metric) and 15.7% (using MAE metric). The SE-ELM predictive model further outperforms the SM-ELM model, with an improvement of 5.3%, using CC computed with training ceramic samples. The simplicity of the employed descriptors, coupled with the outstanding performance of the developed predictive models, would potentially strengthen E2TMO6 ceramics exploration for low-temperature cryogenic applications and circumvent energy challenges in different sectors.

Generalized gradient approximation with Hubbard potential (GGA + U) within the framework of density functional theory (DFT), the structural and electronic properties, as well as the magnetic ordering of the quadruple perovskites Y 2 CuGaTM 4 O 12 (TM = Mn and Fe), are studied. Formation energy indicates that Y 2 CuGaMn 4 O 12 is more stable than the Y 2 CuGaFe 4 O 12 and the estimated structural parameters are in good accordance with the experiment. The optimized magnetic energy curves show that these compounds have a type I ferrimagnetic order. According to the Heisenberg model, strong long-range Mn +3 –O 2− –Cu 2+ –O 2− –Mn +3 interactions are mediated by a super exchange mechanism. The susceptibility data shows that these compounds undergo multiple magnetic transitions due to different magnetic interactions (J 1 (Cu +2 –Cu +2 ), J 2 (Cu +2 –Mn +3 ), and J 3 (Mn +3 –Mn +3 )). The electronic band profiles and density of states shows the half-metallic character of these compounds and Mn d electrons are responsible for their half-metallic nature. Beside this Mn d state electrons are also responsible for magnetism with addition of Cu atoms instead of Ga. DFT and the Heisenberg model's estimated results are confirmed by magnetic susceptibility. These compounds are anticipated to be appropriate for spintronic applications due to their ferrimagnetic nature and high spin polarization near the Fermi level. Graphical Abstract

Investigating valley-related physics in rare intrinsic ferromagnetic materials with high-temperature stability and viable synthesis methods is of vital importance for advancing fundamental physics and information technology. Through first-principles calculations, we forecast that monolayer TiAlTe3 has superb structural stability, a ferromagnetic coupling mechanism deriving from direct-exchange and superexchange interactions, and a high magnetic transition temperature. We observed spontaneous valley polarization of 103 meV in the bottom conduction band when monolayer TiAlTe3 is magnetized toward an out-of-plane orientation. Additionally, because of its powerful valley-contrasting Berry curvature, the anomalous valley Hall effect emerges under an in-plane electric field. The cooperation of ferromagnetic coupling, a high magnetic transition temperature, and spontaneous valley polarization makes monolayer TiAlTe3 a promising room-temperature ferrovalley material for use in nanoscale spintronics and valleytronics.

A novel one-dimensional malleable spin-crossover (SCO) complex [Fe(MPEG-trz)3](BF4)2 has been successfully synthesized by molecular self-assembly between 4-amino-1,2,4-triazoles (MPEG-trz) grafted with a long flexible chain methoxy polyethylene glycol (MPEG) and metallic complex Fe(BF4)2•6H2O. The detailed structure information was illustrated by using FT-IR and 1H NMR measurements, while the physical behaviors of the malleable SCO complexes were systematically investigated by using magnetic susceptibility measurements using superconductivity quantum interference device (SQUID) and differential scanning calorimetry (DSC). This new metallopolymer exhibits a remarkable spin crossover transition behavior, between two spin quantum states (Fe2+ ions): high spin (HS) state (quintet state) and low spin (LS) state (singlet state), at a specific critical temperature with a slender hysteresis loop of 1 K. DFT computations revealed the partial rules of HOMO-LUMO energy levels and spin density distributions of different four-position substituted [Fe(1,2,4-triazole)3]2+ derivatives with different length of repeat units in polymer complexes. This can go a step further to depict the spin and magnetic transition behaviors of SCO polymer complexes. Furthermore, the coordination polymers possess an excellent processability due to an outstanding malleability, which can be easily shaped into a polymer film with spin magnetic switching properties.

Giant magnetostriction could be achieved in MnCoSi-based alloys due to the magneto-elastic coupling accompanied by the meta-magnetic transition. In the present work, the effects of hydrostatic pressure on magnetostrictive behavior in MnCo0.92Ni0.08Si alloy have been investigated. The saturation magnetostriction (at 30,000 Oe) could be enhanced from 577 ppm to 5034 ppm by the hydrostatic pressure of 3.2 kbar at 100 K. Moreover, under a magnetic field of 20,000 Oe, the reversible magnetostriction was improved from 20 ppm to 2112 ppm when a hydrostatic pressure of 6.4 kbar was applied at 70 K. In all, it has been found that the magnetostrictive effect of the MnCo0.92Ni0.08Si compound is strongly sensitive to external hydrostatic pressure. This work proves that the MnCoSi-based alloys as a potential cryogenic magnetostrictive material can be modified through applied hydrostatic pressure.

The structural, magnetocaloric, and magnetic characteristics in Heusler Ni50Mn35In10X5 (X = Ga, Fe, and Al) alloys were examined using X-ray diffraction and field-dependent magnetization measurements. All samples exhibited a mixture structure of cubic L21 and tetragonal L10 and underwent second-order magnetic transitions at TC(Al5) = 220 K, TC(Ga5) = 252 K, and TC(Fe5) = 298 K. The Ga5 alloy exhibited structural change as indicated by a thermal hysteresis that may be seen in the saturation magnetic field in the M(T) dependences. The transition at the TC point from a ferromagnetic to a paramagnetic state caused a drop in magnetization, supported by thermal hysteresis, at a low magnetic field (0.01 T). On the other hand, the Fe5 alloy presented a gradual decrease in magnetization with similar hysteresis behavior, also at a low magnetic field (0.01 T), whereas at 0.1 T of field, no features characteristic of this transition were detected. This could be due to a large difference in the metallic radius of Fe compared to that of In. Otherwise, magnetic investigations demonstrated that the replacement of In with Al may cause the structural transformation temperatures and TC to be shifted to low temperatures. The present results imply that the structural transformation temperatures and the transition itself are highly dependent on chemical composition. Furthermore, under a magnetic field change of 5 T, the maximum magnetic entropy changes of 0.6 J/kg K, 1.4 J/kg K, and 2.71 J/kg K for the Ga5, Fe5, and Al5 alloys, respectively, were determined by their TC. Refrigeration capacity values were found to be 25 J/kg, 74 J/kg, and 98 J/kg at µ0∆H = 5 T. These ribbons are viable candidates for multifunctional applications due to their cheaper cost and their physical characteristics disclosed during the magnetostructural transition, which takes place close to the room temperature.

A solid-state refrigerator device has the potential to overcome the use of greenhouse effect-related gases or hazardous chemicals. Most of these devices work on the basis of magnetocaloric effect (MCE). Ce(Fe 0 . 975 Cr 0 . 025 ) 2 is an engrossing material to study MCE originating from paramagnetic (PM)–ferromagnetic (FM; second-order) transition and FM–antiferromagnetic (first-order) transition. In the present work, the MCE of Ce(Fe 0 . 975 Cr 0 . 025 ) 2 compound, prepared in Arc melting in an argon atmosphere, has been studied. Magnetic entropy change (∆ SM ) and the relative cooling power have been calculated from the M–H curves to characterize the MCE. Direct and inverse MCE are found to be linked with two different magnetic transitions in this compound.

Gd54Fe36B10−xSix (x = 0, 2, 5, 8, 10) amorphous ribbons were fabricated by melt-spinning technique. Based on the molecular field theory, the magnetic exchange interaction was analyzed by constructing the two-sublattice model and deriving the exchange constants JGdGd, JGdFe and JFeFe. It was revealed that appropriate substitution content of Si for B can improve the thermal stability, maximum magnetic entropy change and widened table-like magnetocaloric effect of the alloys, while excessive Si will lead to the split of the crystallization exothermal peak, inflection-like magnetic transition and deterioration of magnetocaloric properties. These phenomena are probably correlated to the stronger atomic interaction of Fe-Si than that of Fe-B, which induced the compositional fluctuation or localized heterogeneity and then caused the different way of electron transfer and nonlinear variation in magnetic exchange constants, magnetic transition behavior and magnetocaloric performance. This work analyzes the effect of exchange interaction on magnetocaloric properties of Gd-TM amorphous alloys in detail.

Ni 0.93-x Zn 0.07 Li x O ( x  = 0, 0.01, 0.03 and 0.05) and Ni 0.92 Zn 0.07 Fe 0.01 O samples were prepared following a simple cost effective wet chemical route. XRD characterization along with Rietveld refinement indicated that the samples crystallize in the fcc phase of host NiO without forming any impurity phases. The crystallite size of the parent Ni 0.93 Zn 0.07 O sample is reduced either by Li or Fe co-doping. Photoluminescence study revealed that the Li co-doping into Ni 0.93 Zn 0.07 O led to the suppression of UV emission intensity along with the shifting of emission towards the blue region. The magnetic study revealed that the all samples exhibit weak ferromagnetism in the antiferromagnetic background of NiO. Arrott plot with negative slope in Zn-doped and (Li, Zn) co-doped NiO samples illustrates the first-order magnetic transition. This in contrast with the observation of (Fe, Zn) co-doped NiO sample where the second-order magnetic transition with positive slope in Arrott plot is appeared. All the samples show robust exchange bias and coercivity features at room temperature. Our study indicated that these samples could be useful for multifunctional device applications.

The characteristic behavior of magnetic remanence correlated with mineralogical textures and composition was observed using low-temperature magnetometry, microscopy, and chemical analysis of three isocubanite samples collected from hydrothermal deposits in the Okinawa Trough and a sample transformed from natural cubanite via heating. Both zero-field remanence acquired at 5 K and field cooling remanence acquired at 300–5 K of all samples sharply decreased with increasing temperature at approximately 100 K. In addition, low-temperature cycling of isothermal remanence at 300 K exhibited a transition at approximately 100 K; remanence increased with decreasing temperature and vice versa. The intensity of remanence at low temperature and sharpness of the transition varied across samples with different compositions and microscopic textures, that is, the presence or absence of chalcopyrite lamellae and their widths. The sample obtained from a hydrothermal chimney, in which the magnetic transition was most clearly observed, was also subjected to X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, and magnetic hysteresis measurements. The obtained results were generally consistent with those reported previously for unnamed mineral CuFe 3 S 4 with an ordered cation arrangement. The low-temperature magnetic behavior of isocubanite possibly depends on the degree of cation ordering and can be regarded as an indicator of chemical composition and cooling history. Therefore, low-temperature magnetometry is useful for the detection of isocubanite and a potentially powerful technique for the prompt estimation of its composition and texture, contributing to our understanding of the formation process of hydrothermal deposits.