The magnetic, dielectric and photocatalytic properties of Fe and Ni co-doped Co3O4 nanoparticles (NPs) were studied in detail. XRD was done for the phase formation and structural analysis, which confirmed pure spinel phase of Co3O4 using Rietveld refinement. The average crystallite size was calculated using refinement data which showed an increase from 16 to 32 nm with co-doping due to increased crystal growth and defects. Surface morphology was studied by using TEM analysis which revealed non-spherical shaped NPs with dense agglomeration having average particles size of 120 nm for undoped and 137 nm for FN44 co-doped, respectively. The increase in average particle size with co-doping is associated with increased crystal growth caused by co-dopants. Magnetic measurements indicate the onset of ferromagnetism (FM) with co-doping which gets strengthen with increasing Fe doping and maximum magnetization was attained for FN62 sample (6

The impact of iron (Fe) and calcium (Ca) co-dopants on the magnetic and photocatalytic properties of nickel oxide (NiO) nanoparticles (NPs) has been studied in detail. Rietveld refinement of the XRD patterns verified the phase formation of NiO without any impurity phases. The average crystallite size was found to decrease with co-doping from 31.90 nm to 20.95 nm, associated with the presence of strain and formation of defects due to different ionic radii of Fe2+/Fe3+ and Ca2+ co-doped ions. The average particle size as calculated from TEM images was 45 and 34.71 nm for undoped NiO and Ni0.92Fe0.04Ca0.04O (FeCa44) samples, respectively. The EDX results verified the presence of all the essential compositional elements like Ni, O, Fe and Ca with appropriate elemental composition. FTIR spectra exhibited the relevant stretching bands of NiO, signifying the successful synthesis of the samples. Temperature-dependent M-H loops were analyzed by using modified Bloch's law for all the co-doped samples. A room-temperature ferromagnetism was revealed in Ni0.92Fe0.06Ca0.02O (FeCa62) and FeCa44 samples, induced by co-dopants due to uncompensated magnetic moments and modified magnetic exchange interactions. Furthermore, the frequency-dependent AC susceptibility data was analyzed to study the spin-glass behavior using different models. The fitted results verified the presence of spin-glass behavior in the co-doped samples due to frustrated and disordered spins. UV-Visible spectroscopy results revealed a red shift in the optical bandgap of co-doped samples, which has a range from 3.83 to 3.70 eV. The photocatalytic results revealed 92 % degradation efficiency of the FeCa62 sample for MO dye, which has the highest degradation value as compared to other samples. The induced ferromagnetism and spin glass response of the co-doped Fe-Ca samples have many applications in memory devices and spintronics. The improved photocatalysis can also be useful for environmental remediation.

The controlled tuning of the volume fraction in magnetic nanoparticle (NP) assemblies provides an effective route to stabilize the interaction-driven glassy magnetic dynamics. We demonstrate that the low-volume-fraction FeCo NP assemblies exhibit clear signatures of a superspin-glass-like state, including characteristic aging, and memory effects, arising from collective freezing mediated by long-range dipolar interactions. An enhancement of low-temperature coercivity in the low-volume fraction NPs system suggests the emergence of interaction-induced effective anisotropy. The present work establishes NPs' volume fraction as a scalable control parameter for engineering collective magnetic states and demonstrates a versatile strategy for designing NP-based magnetic materials with dynamic response.

Orthorhombic air-stable two-dimensional (2D) antiferromagnet (AFM) CrSBr has attracted much research interest lately thanks to its rich magnetic behaviors together with its remarkable electronic, excitonic, and polaritonic properties. Here, we report a reliable electrochemical intercalation method by inserting large tetrabutylammonium (TBA+) ions into CrSBr layers. Magnetically, such intercalation efficiently suppresses the interlayer AFM and induces a ferromagnetic (FM) order with a much-enhanced transition temperature up to 200 K, nearly 70 K higher than the AFM onset of 132 K in pristine CrSBr. Electronically, the TBA+ intercalation not only increases the electric conductivity of CrSBr, which is further enhanced by magnetic fields, but also introduces a giant negative irreversible magnetoresistance. This work demonstrates the tunable magnetic and electronic properties of CrSBr as well as their interplay, paving the way for advanced spintronic and magnetic memory devices.

How “hard” (coercive) can a ferromagnet be? This is a good question and the answer has been a puzzle for a century. Magnetic coercivity is the most important property for permanent magnets in most advanced applications. Efforts for many decades to understand coercivity mechanisms have been made, however the puzzle remains unsolved that prevents us from developing more permanent magnets for the ever-increasing application demands. To date, it is still highly challenging to predict and calculate coercivity in any type of magnets. Eighty years ago, William Fuller Brown offered his famous theorem to correlate coercivity with the magnetocrystalline anisotropy in ferromagnetic materials. In practice, however the experimental coercivity values have been far below the calculated levels given by the theorem, leading to so-called Brown's Paradox. Progress has been made in the past twenty years in understanding coercivity mechanisms in nanoscale low-dimensional ferromagnets, including nanoparticles, thin films and particularly nanowires. A systematic study on the Co nanowires with extraordinarily high coercivity above the magnetocrystalline anisotropy field has opened a door to solving the Brown's paradox and to conduct Anisotropy Engineering of future permanent magnets.

Permanent magnetic thick films are increasingly used in Micro-Electro-Mechanical Systems (MEMS) devices, but the interplay between magnetic properties, microstructure, and film thickness remains underexplored. We deposited SmCo-based films with thicknesses ranging from 350 nm to 1300 nm using magnetron sputtering at room temperature, followed by in-situ annealing. Our study examined the evolution of microstructure, phase composition, magnetic properties, and domain structures as thickness increases. The films displayed dense, fibrous structures typical of the zone T-type region, with 3D morphologies forming a network structure and an arc-shaped surface that expands with thickness. At thinner levels (around 350 nm), an amorphous SmCo phase predominates, prone to oxidation, while at greater thicknesses, the SmCo5 phase dominates but maintains a grain size of 12-15 nm. Coercivity decreases significantly from 33 kOe to 8 kOe as thickness increases from 630 to 1300 nm due to the diminishing pinning effect and dominance of the reversal domain nucleation mechanism. Analysis using magnetic force microscopy and micromagnetic simulations indicates that this reduction in coercivity is mainly due to the decomposition of the SmCo5 phase and a reduction in magnetic domain size.

The magnetic kagome lattice compound RMn6Sn6 (R=rare earth) is an emerging platform to exploit the interplay between magnetism and topological electronic states where a variety of exciting findings such as flat bands, Dirac points as well as the dramatic dependence of magnetic order on the rare-earth element have been reported. High entropy through rare earth alloying, on the other hand, provides another knob to control over the physical properties in this system. Here, by the marriage of high entropy and the magnetic kagome lattice, we obtain (Gd,Tb,Dy,Ho,Er)Mn6Sn6 single crystals and systematically investigate their magnetic and transport properties. Different from the parent phases, the high entropy 166 material displays multiple novel magnetic transitions induced by temperature and external magnetic fields. Furthermore, linear magnetoresistance persisting up to 20 T has been revealed at 4 K. The intrinsic nontrivial band topology also survives in the high entropy form, as evidenced by the intrinsic anomalous Hall effect. Our results highlight high entropy as a powerful approach for tuning the interplay of charge, spin and lattice degree of freedom in magnetic topological materials.

The study reports a magnetocaloric effect (MCE) in the FeMnO3 bixbyite compound prepared via autocombustion technique using nitrate salts. The X-ray diffraction (XRD) study showed that FeMnO3 assumes a cubic phase with a space group Ia-3. X-ray photoelectron spectroscopy (XPS) study confirmed the oxidation states of Fe3+ and Mn3+. Temperature-dependent magnetization measurements revealed the presence of antiferromagnetic ordering in the compound at around 40 K. The effective magnetic moment, µeff, was calculated as 2.36 µB from the susceptibility curve. Change in maximum magnetic entropy ǀ∆SMaxǀ, determined from magnetic isotherms, is approximately 4.14 Jkg−1 K−1 at 65 K under 5 T applied field, leading to higher relative cooling power, RCP as 200.29 Jkg−1. Specific heat capacity, ∆Cp, and temperature-averaged entropy change, TEC, were also analyzed to study magnetic cooling efficiency. This study observed that FeMnO3 displays potential MCE performance, making it a promising candidate for magnetic refrigeration applications.

Magnetic anisotropy is essential for many applications of ferromagnetic/ferrimagnetic materials, including permanent magnets and magnetic recording media. Attempts have been made recently to build up 3-D nanoparticle and quantum dot assemblies, however, it is not understood yet if a nanoparticle assembly can possess high magnetic anisotropy with low anisotropic materials. In this article, we report our discovery of high magnetic anisotropy resulted from Fe3O4 nanoparticle chains. We started with closely-packed nanoparticle assemblies of spherical Fe3O4 nanoparticles that exhibit low magnetocrystalline anisotropy and shape anisotropy, and corresponding negligible coercivity. When the nanoparticle assemblies are compressed under pressure, they form bundles or arrays that consist of Fe3O4 chains with a length scale of several hundred nanometers. Magnetic measurements show that these Fe3O4 chain arrays possess a high uniaxial magnetic anisotropy (Keff ~ 2.9×105 J/m³) and significant magnetic coercivity. Our simulations reveal that interparticle magnetic dipolar interactions contribute to this type of superstructure magnetic anisotropy. This study demonstrates the feasibility and approaches to create "patterned" high magnetic anisotropy in nanoparticle superstructures/assemblies.

The effect of manganese (Mn) substitution on the magnetic properties of SrFe8−xMnxAl4O19 nanocrystals has been investigated via precise compositional modulation with x = 0, 0.25, 0.50, 0.75, and 1.0. Rod-shaped nanocrystals with hexagonal crystal structure and an average crystallite-size of 25 nm were synthesized via sol-gel method. Magnetic property measurements have been conducted including hysteresis loops and singular point detection (SPD) to investigate the impact of Mn-substitution on magnetic hardening of SrFe8Al4O19 nanocrystals. An increase in Mn-concentration from x = 0 to x = 1.0 resulted in a significant increase in magnetic coercivity from 12.5 to 17 kOe. This increasing trend in coercivity with higher Mn-content is attributed to the enhanced magnetocrystalline anisotropy (MCA). Further, Bloch’s law fittings of the temperature-dependent magnetization data revealed an increase in the value of Bloch’s constant B with an increase in Mn-content, indicating weak exchange interactions that effectively boosted the magnetic anisotropy and increased the coercivity.

The modulation of the magnetic and electronic properties of 1T-CrS2 monolayer through hydrogenation is systematically investigated from first principles. The hydrogenated CrS2 monolayer exhibits both dynamical and thermal stabilities at room temperature. The magnetic ground state of CrS2 monolayer transforms from a 120 degrees noncollinear antiferromagnetic state to a ferromagnetic state upon hydrogenation, accompanied by the transition from metal to semiconductor. These transitions can be attributed to the induced tensile strain and charge redistribution resulting from the adsorption of hydrogen. When hydrogen is adsorbed on both sides of CrS2, the estimated ferromagnetic transition temperature of CrS2-2H monolayer is 310 K, and it can be further enhanced to 430 K under a compressive strain of-4%. Moreover, by performing 0.05 hole or 0.05 electron doping in CrS2-2H monolayer, 100% spin polarization at the Fermi energy in either the spin-down or spin-up channel can be effectively achieved, indicating that a double-gate-controlled field-effect spin filter based on CrS2-2H monolayer can be designed for potential application in spintronic devices.

In this study, FeCo nanoparticles are synthesized using the chemical solution approach. XRD pattern shows cubic crystal structure with the average crystallite size of 19 nm. The nanoparticles exhibit a high saturation magnetization of 230 emu/g with a coercivity of 268 Oe at room temperature. The sharp increase in the ZFC magnetization with temperature till ∼50 K of random nanoparticles indicates the relaxation of randomly oriented surface and superspins. However, the sharp increase in the ZFC magnetization of aligned nanoparticles is not observed in this temperature range, which implies that the superspins were already aligned and did not get relaxed due to the existence of strong dipolar interactions. This observation is interpreted as the dominance of dipolar interactions over the superspin relaxation. The flat FC curve for randomly oriented nanoparticles is an evidence for the existence of strong dipolar interactions, which further get increased with the alignment of nanoparticles. The sharp decrease in the FC magnetization of the aligned sample with the decreasing temperature is an interesting feature that may be due to the existence of enhanced interparticle magnetic dipolar interactions in the aligned nanoparticles. Furthermore, the sharp increase in coercivity below 50 K is also attributed to the anisotropy induced by the surface and superspin dipolar interactions. More importantly, the coercivity of the randomly oriented nanoparticles at 5 K is observed to be 416 Oe which got increased by ∼2 times (780 Oe) for the aligned sample, further confirming the presence of anisotropy induced by the strong magnetic dipolar interactions. The emergence of significant anisotropy from the aligned nanoparticles via dipolar interactions makes it an interesting system for further investigations.

Flexible Light Emitting Diodes are versatile lighting solutions that offer bendable and adaptable illumination possibilities. A soft, flexible white luminescent film (1 mm) shows promise for foldable electroluminescent devices and applications. This film was fabricated using ZnS:Ag and Mn. Under different excitation wavelengths, the phosphors emit blue light due to Ag+ luminescence centers and red light from the d-d transition of Mn2+. The blue emission is greatly suppressed at high Mn2+ doping levels, requiring reduced Ag+ doping in co-doped ZnS:Ag,Mn compared to solo-doped ZnS:Ag samples. By adjusting Ag+ and Mn2+ concentrations, the ZnS:Ag(1%),Mn(0.2%) phosphors show a proper intensity ratio of blue and red emissions, making them a promising candidate for future white light applications.

SmCo based films with excellent intrinsic magnetic properties have promising applications in microelectro-mechanical system (MEMS). However, due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film, both the coercivity (Hc) and remanence (Mr) of films are difficult to enhance simultaneously. In this paper, SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process. The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed. By adjusting the Sm/Co atomic ratio from 1:5 to 1:4, Co soft magnetic phase disappears and the single phase SmCo5 is obtained, leading to the increase of coercivity of the films from 30 to 34 kOe. The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated. When the deposition temperature increases from room temperature to 250 degrees C, the coercivity will further increase from 34 to 51 kOe. However, a severe kink is observed in the demagnetization curves due to the poor exchanged coupling. An analysis of transmission electron microscopy (TEM) confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5, which contributes to the decoupling and low remanence ratio. Therefore, doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films. Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced. We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization, which can be utilized in high performed MEMS devices. (c) 2023 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights are reserved, including those

Sm-Co-based films play an irreplaceable role in special applications due to their high curie temperature and magnetocrystalline anisotropic energy, especially in heat-assisted magnetic recording (HAMR), but the complex composition of Sm-Co phase and unclear synergistic coupling mechanisms of multi-elemental doping become the challenges to enhance the properties. In this work, a novel strategy combining magnetron sputtering and a high-throughput experiment method is applied to solve the above-mentioned problems. Fe/Cu co-doping highly increases the remanence while maintaining a coercivity larger than 26 kOe, leading to an enhancement of the magnetic energy product to 18.1 MGOe. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) reveals that SmCo5 phase occupies the major fraction, with Co atoms partially substituted by Fe and Cu atoms. In situ Lorentz transmission electron microscopy (LTEM) observations show that the Sm (Co, Cu)(5) phase effectively prohibits domain wall motions, leading to an increase of coercivity (H-c). Fe doping increases the low saturation magnetization (M-s) and low remanence (M-r) due to the Fe atom having a higher saturation magnetic moment. The magnetization reversal behaviors are further verified by micromagnetic simulations. Our results suggest that Sm-Co-based films prepared via Fe/Cu co-doping could be a promising candidate for high-performed HAMR in the future.

Caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), coronavirus disease 2019 (COVID-19) has shown extensive lung manifestations in vulnerable individuals, putting lung imaging and monitoring at the forefront of early detection and treatment. Magnetic particle imaging (MPI) is an imaging modality, which can bring excellent contrast, sensitivity, and signal-to-noise ratios to lung imaging for the development of new theranostic approaches for respiratory diseases. Advances in MPI tracers would offer additional improvements and increase the potential for clinical translation of MPI. Here, a high-performance nanotracer based on shape anisotropy of magnetic nanoparticles is developed and its use in MPI imaging of the lung is demonstrated. Shape anisotropy proves to be a critical parameter for increasing signal intensity and resolution and exceeding those properties of conventional spherical nanoparticles. The 0D nanoparticles exhibit a 2-fold increase, while the 1D nanorods have a > 5-fold increase in signal intensity when compared to VivoTrax. Newly designed 1D nanorods displayed high signal intensities and excellent resolution in lung images. A spatiotemporal lung imaging study in mice revealed that this tracer offers new opportunities for monitoring disease and guiding intervention.

Oligomerization presents a wide range of opportunities for transforming light olefins into liquid fuels. This study centers on a novel catalyst system - phosphotungstic acid (PW) loaded onto MCM-41 prepared via impregnation, aiming to tackle these challenges. The ordered mesoporous structure, high surface area, and facile recovery of MCM-41 make it an ideal support for PW. Under the mild reaction conditions of 70 degrees C, 1 MPa, and 5 h, the 20% PW/MCM-41 catalyst exhibited remarkable catalytic performance, achieving an isopentene conversion rate of 77.8%, a selectivity of 93.5% towards the C10 dimer product, and a yield of 72.7%. Encouragingly, the catalyst could be reused without special treatment, maintaining a selectivity above 93% for the C10 dimer product over five cycles, showcasing outstanding stability and regeneration capability. This research not only provides robust insights into catalyst design for isopentene dimerization but also paves the way for sustainable advancements in industrial catalysis.

The study reports the synthesis and magnetocaloric properties of the rare-earth element as Eu3+ doped La1.4Ca1.6Mn2O7-Mn3O4 composites prepared by the one-pot autocombustion technique. Eu3+ co-doping enhanced the Curie temperatures from 181 K for La1.4Ca1.6Mn2O7 (LCMO) to 186 K for La1.3Ca1.6Eu0.1Mn2O7 perovskites, which consequently enhanced the relative cooling power value of the compound. Moreover, these composites were also prepared in the presence of 10 wt% of Mn3O4 nanoparticles. The presence of Mn3O4 at the intervening grain boundaries between La1.4Ca1.6Mn2O7 (A) and La1.3Ca1.6Eu0.1Mn2O7 (B) phases altered the double exchange interaction between Mn3+ and Mn4+ ions. The temperature-dependent field-cooled magnetization curves showed that these nanocomposites' interfacial magnetic interactions significantly expanded the second-order ferromagnetic-to-paramagnetic phase transition temperature. This further enhanced the magnetic entropy magnitudes |Delta S-Max| up to 0.521 J kg(-1) k(-1) and the associated relative cooling power value to 43.67 J kg(-1) under a 5T applied magnetic field. The temperature-averaged entropy change (TEC) values of composites outperformed the individual values of samples A and B between the temperature range of 80-240 K. The fundamental key of this work is to demonstrate the potentiality of enhancing the magnetic phase transition temperature and magnetocaloric effect in the framework of interfacial coupling between LCMO and the Mn3O4 phases of the nanocomposites.

Nucleation underpins a vast range of phase-transition phenomena in many disciplines. Critical to revealing nucleation thermodynamics and kinetics is the understanding of the nucleus structure at its early stage. Typically, it is assumed that nucleation is a sudden local structural transition from one phase to another. Here, we are able to access fundamental steps in the nucleation from amorphous phase by a combination of molecular simulations and experimental observation. We discover a surprising pathway of semicrystalline nucleation where one of the materials components crystallizes and another remains amorphous between the crystalline planes in the nuclei. The early-stage crystallization nucleus is robustly evidenced to undergo a gradual ordering and densification, originating from the presence of diffuse interfaces, and renders an ultralow interfacial energy that is orders of magnitude lower than those typically used in various formulations of nucleation. Our study provides critical information and insight for the early stages of nucleation that determine how crystallization is initiated and benefits controllable synthesis of materials.