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In this study, the structural, optical, and magnetic properties of the Zn0.5Ni0.5Fe2O4 soft ferrite nanoparticle, the Ba0.4Sr0.4Ca0.2Fe12O19 hard ferrite nanoparticle, and their nanocomposite (Zn0.5Ni0.5Fe2O4)0.5(Ba0.4Sr0.4Ca0.2Fe12O19)0.5 have been investigated. The nanoparticles and the nanocomposite were synthesized via co-precipitation and ball-milling routes, respectively. The formation, purity, and crystallinity of the samples were verified from the Rietveld analysis of X-ray diffraction (XRD) data as well as the essential absorption bands in the Fourier transform infrared (FTIR). The morphology and lattice spacing were investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED). TEM micrographs visualized the hexagonal morphology of Ba0.4Sr0.4Ca0.2Fe12O19 phase and the spherical-like shape of Zn0.5Ni0.5Fe2O4 phase. A scanning electron microscope (SEM) revealed well-distributed grains in the composite. Furthermore, energy-dispersive X-ray analysis (EDX) analysis validated the chemical compositions and the coexistence of Zn0.5Ni0.5Fe2O4 and Ba0.4Sr0.4Ca0.2Fe12O19 phases in one matrix. Additionally, the optical behavior of the samples was tested via ultraviolet–visible and photoluminescence spectroscopies. Tauc plots were used to estimate the direct energy gap using UV spectroscopy. The direct and indirect energy band gaps of (Zn0.5Ni0.5Fe2O4)0.5(Ba0.4Sr0.4Ca0.2Fe12O19)0.5 nanocomposite are in between that of the pure phases, due to the increase in energy states with particle size. Also, near-band edge emissions and deep-level emissions have been observed in PL studies. X-ray photoelectric spectroscopy (XPS) studies were performed to investigate the elemental composition and cationic distribution. A good exchange coupling between both nanoparticles was verified via a single-phase behavior in the magnetic hysteresis loop. (Zn0.5Ni0.5Fe2O4)0.5(Ba0.4Sr0.4Ca0.2Fe12O19)0.5 nanocomposite had a higher saturation magnetization ( M s ) compared to Ba0.4Sr0.4Ca0.2Fe12O19 phase and a squareness ratio (SQR) of 0.207 value ( < 0.5) , making it suitable for use in magnetic hyperthermia, the production of permanent magnets, and extremely sensitive for magnetic recording media. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphors activated by Cr3+ ions are critical for developing NIR phosphor‐converted light‐emitting diodes (pc‐LEDs). The temperature‐dependent behaviors of the narrowband 2E → 4A2 and broadband 4T2 → 4A2 transitions of Cr3+ ions differ, which makes Cr3+‐activated phosphors highly promising for ratio optical thermometers. How to obtain Cr3+‐activated phosphors with both high luminescence efficiency and thermal stability is a challenge. Herein, a strategy of adjusting the doping levels is adopted to precisely control the exchange coupling between Cr3+ ions in LiAl5O8: Cr3+ phosphors. As Cr3+ ions doping concentration increases, the NIR emission shifts from narrowband to broadband. Under heavy doping concentrations, the sample exhibits an unusual broadband emission in a strong crystal field, covering 645 to 1300 nm, with a peak emission wavelength of 950 nm and a FWHM of 295 nm. Simultaneously, a high internal quantum efficiency (IQE = 85%) and excellent thermal stability (I423K/I293K = 86%) are achieved, highlighting the broad application potential of the developed NIR pc‐LEDs. Interestingly, under low‐concentration doping, the sample exhibits dual emission characteristics, and the temperature dependence of its two emission peaks shows opposite trends. Utilizing fluorescence intensity ratio (FIR) technology, the sample achieves a relative sensitivity of 0.30% K⁻¹, highlighting its promising potential for temperature sensing applications. [ABSTRACT FROM AUTHOR]

Understanding and controlling the magnetic behavior of nanowire (NW) arrays is a fundamental step for developing novel future-generation devices. The current research investigated the role of copper pre-plating thickness on the structural and magnetic interactions of cobalt NW arrays. The NWs were grown in the anodic aluminum oxide (AAO) templates with a nanopore diameter of 30 nm by using a pulse electrodeposition (PED). The thickness of Cu pre-plating varied by adjusting the amount of electrodeposition (ED) Coulomb charge to about 0.03–0.7 C. The intensity of the Co-hcp peaks in the X-ray diffraction (XRD) pattern changes with the increase of Cu pre-plating, which can be related to ion mobility and growth kinetics during the ED process. The hysteresis curves indicate that effective magnetic anisotropy fields ( H A eff) increase from 7200 to 11,000 Oe with increasing Cu thickness. The coercivity of Co nanowire arrays without Cu pre-plating was 1170 Oe and rose to 1870 Oe for optimum Cu thickness with 0.3 C pre-plating. The switching field distribution (SFD) extracted from hysteresis curves agrees well with the squareness ratio. Also, the SFD indicates an exchange coupling between the interfaces of the magnetic phases in the optimum sample. The regions formed in the first-order reversal curve (FORC) diagram showed crystalline features and magnetic phase interactions between the intra and inter-wire. Further, the FORC analysis showed the same crystalline features as those obtained from the XRD structural analysis. [ABSTRACT FROM AUTHOR]

Magnetic exchange coupling (J) is one of the important spin Hamiltonian parameters that control the magnetic characteristics of single‐molecule magnets (SMMs). While numerous chemical methodologies have been proposed to modify ligands and control the J value, and magneto‐structural correlations have been developed accordingly, altering this parameter through non‐chemical means remains a challenging task. This study explores the impact of an Oriented‐External Electric Field (OEEF) on over twenty lanthanide‐radical complexes using Density Functional Theory (DFT) and ab initio Complete Active Space Self‐Consistent Field (CASSCF) methods. Five complexes – [{(Me3Si)2N]2Gd(THF)}2(μ‐η2:η2‐N2)] (1), [Gd(Hbpz3)2(dtbsq)] (2), [Gd(hfac)3(IM‐2py)] (3), [Gd(hfac)3(NITBzImH)] (4), and [Gd(hfac)3{2Py‐NO}(H2O)] (5) – were selected for detailed analysis, revealing significant OEEF effects on magnetic exchange interactions and structural parameters. Various parameters such as bond distances, bond angles, and torsional angles were examined as a function of OEEF to establish guiding principles for molecule selection. In complexes 1, 2, and 3, OEEF influenced torsional angles and altered exchange interactions. Complex 4 demonstrated enhanced ferromagnetic coupling under OEEF, reaching a maximum J value of +5.3 cm−1. Complex 5 reveals switching the sign of JGd‐rad exchange interaction from antiferromagnetic to ferromagnetic under OEEF, highlighting the potential of electric fields in designing materials with tuneable magnetic properties. These findings offer valuable insights for future research and applications in advanced materials and molecular electronics. [ABSTRACT FROM AUTHOR]

The generally accepted model of the magnetic structure of an iron oxide core–shell nanoparticle includes a single-domain magnetically ordered core surrounded by a layer with a frozen spin disorder. Due to the exchange coupling between the shell and core, the spin disorder should lead to nonuniform magnetization in the core. Suppression of this inhomogeneity by an external magnetic field causes the nonlinear behavior of the magnetization as a function of the field in the region of the approach to magnetic saturation. The equation proposed to describe this effect is tested using a micromagnetic simulation. Analysis of the approach to magnetic saturation of iron oxide nanoparticles at different temperatures using this equation can be used to estimate the temperature evolution of the core–shell coupling energy and the size of the uniformly magnetized nanoparticle core and the temperature behavior of this size. [ABSTRACT FROM AUTHOR]

Pure NiO, BaFe12O19, and Ni0.5Zn0.5Fe2O4 nanoparticles were synthesized by the co-precipitation method. Four ternary (1 − x–y)NiO/xNi0.5Zn0.5Fe2O4/yBaFe12O19 (x and y between 0 and 1) nanocomposites (NCs) were prepared by the wet ball milling technique, then calcined at 950 °C for 4 h. The X-ray powder diffraction (XRD) validated the production of pure NiO and Ni0.5Zn0.5Fe2O4 without impurities, while BaFe12O19 was produced with the α-Fe2O3 additional phase. When compared to the initial weight percentages, the Rietveld refinement technique revealed different weight percentages for the three phases. The transmission electron microscope (TEM) and the selected area electron diffraction (SAED) investigated the morphology and the microstructure of the samples, respectively. X-ray photoelectron spectroscopy (XPS) showed that nanocomposites were successfully formed from the examination of the elements constituting the nanocomposites (Ba2+, Ni2+, Ni3+, Zn2+, Fe3+and O2−). The vibrating sample magnetometer (VSM) measurements identified the effect of the weight percentage of each phase in the nanocomposite on the magnetic parameters. The switching field distribution (SFD) curves indicated significant exchange coupling interactions in the samples that include a small weight percentage of BaFe12O19. Exchange and dipolar interactions were both recognized in Henkel plots of all samples, although exchange coupling predominated. Four laws of approach to saturation (LAS) were applied to the samples and showed magnetization dependency on H−1 and H−1/2 rather than the summation of H−1, H−2, and H for almost all samples. [ABSTRACT FROM AUTHOR]

Extensive research has been conducted over the last decade to develop permanent magnets utilizing less rare earth materials. Exchange-coupled nanocomposite magnets are a fascinating development in the field of permanent magnets. They involve the combination of hard and soft ferrites, resulting in a unique and evolving magnet. Here we present an in-depth structural, morphological and magnetic characterization of ferrite-based nanostructures obtained through a bottom-up sol−gel approach. The combination of high coercivity of a hard phase SrFe9.8Al2La0.2O19 (SFALO) and high saturation magnetization of a soft phase, Co0.7Zn0.3Fe2O4 (CZFO), allowed us to develop exchange-coupled bi-magnetic nanocomposites by varying the mass percentage (x = 0, 0.1, 0.2, 0.3, 0.4, 1). Thermogravimetric analysis (TGA) up to 1200 °C was used to investigate the material’s thermal properties with the phase formation temperature. Detailed atomic/nano-scale structural characterizations of these nanocomposites were performed by X-ray diffraction and Transmission Electron Microscopy. The average particle size was calculated from the SEM analysis and it was observed that most of the composites with ratio x = 0.1, 0.3 & 0.4 was 145 nm and x = 0.2 was 165 nm. The Switching Field Distribution (SFD) curve revealed the exchange coupling between soft and hard magnetic particles. The findings indicate that the inclusion of a soft magnetic phase has a considerable impact on the exchange coupling between the hard and soft ferrite phases. As the spinel concentration increased, in the composite the saturation magnetization increased from 18 emu/g to 48 emu/g. From the stroner-wholfrath model, the decrease in the remanence ratio below 0.5 concludes the crystallites are randomly oriented. The nanocomposite with the ratio x = 0.1 was observed with the high magneto crystalline anisotropy of 2183.23 × 102 (J/m3) and a high energy product (BH)max of 5.5 kJ/m3. The aforementioned features of nanocomposites demonstrate their potential for use in permanent magnet applications.

Bimetallic colloidal CoPt nanoalloys with low platinum content were successfully synthesized following a modified polyol approach. Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) studies were performed to estimate the crystal structure, morphology, and surface functionalization of the colloids, respectively, while the room-temperature magnetic properties were measured using a vibrating sample magnetometer (VSM). The particles exhibit excellent uniformity, with a narrow size distribution, and display strong room-temperature hysteretic ferromagnetic behavior even in the as-made form. Upon annealing at elevated temperatures, progressive formation and co-existence of exchange coupled, of both chemically ordered and disordered phases significantly enhanced the room-temperature coercivity. [ABSTRACT FROM AUTHOR]

Catalysts promoting multielectron charge delocalization offer selectivity for the CO2reduction reaction (CO2RR) over the competing hydrogen evolution reaction. Here, we show metal-ligand exchange coupling as an example of charge delocalization that can determine the efficiency for photocatalytic CO2RR. A comparative evaluation of iron and cobalt complexes supported by the redox-Active ligand tpyPY2Me establishes that the two-electron reduction of [Co(tpyPY2Me)]2+([Co]2+) occurs at potentials 770 mV more negative than the [Fe(tpyPY2Me)]2+([Fe]2+) analogue by maximizing the exchange coupling in the latter compound. The positive shift in the reduction potential promoted by metal-ligand exchange coupling drives [Fe]2+to be among the most active and selective molecular catalysts for photochemical CO2RR reported to date, maintaining up to 99% CO product selectivity with total turnover numbers (TONs) and initial turnover frequencies exceeding 30,000 and 900 min-1, respectively. In contrast, [Co]2+shows much lower CO2RR activity, reaching only ca. 600 TON at 83% CO product selectivity under similar conditions accompanied by rapid catalyst decomposition. The spin density plots of the two-electron reduced [Co]0complex implicate a paramagnetic open-shell doublet ground state compared to the diamagnetic open-shell singlet ground state of reduced [Fe]0, rationalizing the observed negative shift in two-electron reduction potentials from the [M]2+species and lowered CO2RR efficiency for the cobalt complex relative to its iron congener. This work emphasizes the contributions of multielectron metal-ligand exchange coupling in promoting effective CO2RR and provides a starting point for the broader incorporation of this strategy in catalyst design.

The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions. [ABSTRACT FROM AUTHOR]

A complete theoretical analysis using first the simple Hückel model followed by more sophisticated multi‐reference calculations on a trinuclear Ni(II) complex (Tp#Ni3HHTP), bearing the non‐innocent bridging ligand HHTP3−, is carried out. The three semiquinone moieties of HHTP3− couple antiferromagnetically and lead to a single unpaired electron localized on one of the moieties. The calculated exchange coupling integrals together with the zero‐field parameters allow, when varied within a certain range, reproducing the experimental data. These results are generalized for two similar other trinuclear complexes containing Ni(II) and Cu(II). The electronic structure of HHTP3− turns out to be independent of both the chemical nature and the geometry of the metal ions. We also establish a direct correlation between the geometrical and the electronic structures of the non‐innocent ligand that is consistent with the results of calculations. It allows experimentalists to get insight into the magnetic behavior of this type of complexes by an analysis of their X‐ray structure. [ABSTRACT FROM AUTHOR]

The generally accepted model of the magnetic structure of an iron oxide core–shell nanoparticle includes a single-domain magnetically ordered core surrounded by a layer with a frozen spin disorder. Due to the exchange coupling between the shell and core, the spin disorder should lead to nonuniform magnetization in the core. Suppression of this inhomogeneity by an external magnetic field causes the nonlinear behavior of the magnetization as a function of the field in the region of the approach to magnetic saturation. The equation proposed to describe this effect is tested using a micromagnetic simulation. Analysis of the approach to magnetic saturation of iron oxide nanoparticles at different temperatures using this equation can be used to estimate the temperature evolution of the core–shell coupling energy and the size of the uniformly magnetized nanoparticle core and the temperature behavior of this size.

Exchange‐coupled spin states of cobalt complexes represent the key to understanding the challenging nature of the magnetism of cobalt dimer. In this study, we introduce a comprehensive investigation of the nature of magnetic super‐exchange coupling interactions between two metallic centers in a macro ligand cobalt dimer. More importantly, we provide a detailed comparison between a series of bridging ligands and study their role in the magnetic exchange coupling constant in cobalt dimer with tetraaza macrocycle ligand scaffold. By varying the types of bridging and terminal ligands, we explored the nature of magnetic coupling in 24 species of cobalt dimers, which allowed us to draw a magneto‐structure relationship and monitor the effect of bridging/terminal ligands on the overall magnetism. We employed different density functional theory (DFT) methodologies and complete active space self‐consistent field (CASSCF) in our investigation. The results show that there are comprehensible functional dependencies, and the choice of exchange‐correlation functional is critical for calculating the magnetic properties. Using the experimental values of the exchange coupling, we found that hybrid functionals with 10–20 % Hartree‐Fock exchange integrals give acceptable accuracy. Furthermore, we adjusted the percentage of HF integrals to estimate the optimum value required to be included in the hybrid functionals. Finally, we used CASSCF to gain deeper understanding of the magnetic coupling for the valence magnetic electrons and to achieve the true ground state wavefunction, which is not feasible with conventional DFT calculations. However, the CASSCF calculations poorly underestimate the magnetic coupling, which can be significantly improved by including the dynamic correlations, as implemented in the NEVPT2 methodology. [ABSTRACT FROM AUTHOR]

The involvement of spin symmetry in the evaluation of zero-field energy levels in polynuclear transition metal and lanthanide complexes facilitates the division of the large-scale Hamiltonian matrix referring to isotropic exchange. This method is based on the use of an irreducible tensor approach. This allows for the fitting of the experimental data of magnetic susceptibility and magnetization in a reasonable time for relatively large clusters for any coupling path. Several examples represented by catena-[AN} and cyclo-[AN] systems were modeled. Magnetic data for 20 actually existing endohedral clusters were analyzed and interpreted. [ABSTRACT FROM AUTHOR]

The Co-Pt binary system can form a two-phase nanochessboard structure comprising regularly aligned nanorods of magnetically hard tetragonal L10 phase and magnetically soft cubic L12 phase. This Co-Pt nanochessboard, being an exchange-coupled magnetic nanocomposite, exhibits a strong effect on magnetic domains and coercivity. While the ideal nanochessboard structure has tiles with equal edge lengths (a = b), the non-ideal or nonstandard nanochessboard structure has tiles with unequal edge lengths (a ≠ b). In this study, we employed phase-field modeling and computer simulation to systematically investigate the exchange coupling effect on magnetic properties in nonstandard nanochessboards. The simulations reveal that coercivity is dependent on the length scale, with magnetic hardening occurring below the critical exchange length, followed by magnetic softening above the critical exchange length, similar to the standard nanochessboards. Moreover, the presence of unequal edge lengths induces an anisotropic exchange coupling and shifts the coercivity peak with the length scale. [ABSTRACT FROM AUTHOR]

To solve the problem of the low coercivity of Nd-Fe-B-based nanowires impeding their application in magnetic storage media, highly ordered Nd-Fe-B/Fe-Co composite nanowires were fabricated in an anodic alumina template by means of the alternating electrochemical deposition method. In this paper, the effect of soft and hard magnetic phase compositing on the magnetic properties of Nd-Fe-B-based nanowires was investigated, and the coercivity improvement mechanism was demonstrated. The results show that after annealing at 600 °C for 2 h, Nd-Fe-B/Fe-Co nanowires crystallize into a multiphase structure containing a hard Nd2(Fe, Co)14B phase and soft NdB4, NdB6, Fe7Nd, and Fe7Co3 phases. It is characterized that the Nd2(Fe, Co)14B phase preferentially nucleates, followed by NdB4 + NdB6 + Fe7Nd, while Fe7Co3 has been formed in as-deposited nanowires. The existence of a Nd2(Fe, Co)14B phase with high anisotropy fields, the remanence enhancement effect produced by exchange coupling between hard–soft magnetic phases, and the pinning effect between different phases make the composite nanowires approximately exhibit single hard magnetic phase characteristics with coercivity and remanence ratio as high as 4203.25 Oe and 0.89. The results indicate that synthesizing Nd-Fe-B/Fe-Co exchange-coupled composite nanowires via alternating electrodeposition is an effective way to optimize the magnetic performance of Nd-Fe-B-based nanowires. [ABSTRACT FROM AUTHOR]

The first-principles calculations of the band structure and magnetic properties of trimethylammonium trichloromanganate dehydrate [(CH3)3NH]MnCl3 × 2H2O crystal within the density functional theory were carried out for the first time. This compound corresponds to the AMeCl3 crystal groups that are intensively studied experimentally due to their unique magnetic properties at low temperatures. To overcome the electronic correlations associated with the availability of Mn atoms in the crystal structure, the Hubbard-like method (GGA + U) was adopted for our calculations. The U parameter was adjusted to reproduce the nearest-neighbor exchange coupling constant. Also, the behavior of the exchange interaction in charge of magnetic character is analyzed. The different magnetic configurations were examined for finding the ground state. The most energy favorable state for [(CH3)3NH]MnCl3 × 2H2O is the antiferromagnetic state with spin-ordering that corresponds to C-type AFM (nearest spins in 1D-chains are antiparallelly aligned). The band structure calculations demonstrate the flatness of the band energy dispersion in the valence band. The presented theoretical results confirm the existent experimental data. Especially, the value of the Neel temperature calculated based on the obtained exchange interaction parameter of [(CH3)3NH]MnCl3 × 2H2O compound corresponds to the experimental one. [ABSTRACT FROM AUTHOR]

We characterize the effect of ferromagnetic nickel nanoparticles (size ∼ 6   n m ) on the magnetotransport properties of chemical-vapor-deposited (CVD) graphene. The nanoparticles were formed by thermal annealing of a thin Ni film evaporated on top of a graphene ribbon. The magnetoresistance was measured while sweeping the magnetic field at different temperatures, and compared against measurements performed on pristine graphene. Our results show that, in the presence of Ni nanoparticles, the usually observed zero-field peak of resistivity produced by weak localization is widely suppressed (by a factor of ∼3), most likely due to the reduction of the dephasing time as a consequence of the increase in magnetic scattering. On the other hand, the high-field magnetoresistance is amplified by the contribution of a large effective interaction field. The results are discussed in terms of a local exchange coupling, J ∼ 6   m e V , between the graphene π electrons and the 3d magnetic moment of nickel. Interestingly, this magnetic coupling does not affect the intrinsic transport parameters of graphene, such as the mobility and transport scattering rate, which remain the same with and without Ni nanoparticles, indicating that the changes in the magnetotransport properties have a purely magnetic origin. [ABSTRACT FROM AUTHOR]

(MgFe 2 O 4) 100-x /(BaFe 12 O 19) x , soft/hard nanocomposites (NCs) having different hard ferrite ratio i.e. x = 0, 25, 50, 75 and 100 have been synthesized via in-situ auto-combustion sol-gel method. XRD patterns ensured the co-existence of both hexaferrite and spinel ferrite phases without any impure phase and no significant difference in average crystallite size was observed. The FTIR and Raman spectra confirmed the fabrication of desired material without any impurity. The absence of blocking peak in the ZFC measurements revealed that the blocking temperature of these NCs lie above room temperature. The M − H loops taken at different temperatures resulted into single smooth curve indicating strong interphase exchange-coupling among hard-soft ferrite phases. The occurrence of shoulder peak in dM/dH versus H curve for molar ratio x = 50 is an indication of weak exchange coupling between the two phases. From modified Block's law fitting, the Block's constant (B) exponentially declined with the addition of hard phase that revealed higher value of exchange-coupling constant J. The complex impedance analysis (Nyquist/Cole-Cole plots) and its simulation using an equivalent model circuit revealed the major contribution of both grains and grin-boundaries toward the total conduction mechanism of the NCs. These findings indicate that the higher value of impedance makes these NCs favorable candidates for numerous technological areas like electromagnetic shielding and high band-pass filters. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties of methane (CH4) heat-treated Sr-hexaferrite powders during the re-calcination process were investigated and compared with the magnetic properties of conventionally synthesized Sr-hexaferrite powder. Gradual changes in the magnetic behavior of the produced powder in each re-calcination stage were investigated using magnetization curves obtained from the vibration sample magnetometry (VSM) technique. First, the initial Sr-hexaferrite powder was prepared by the conventional route. Then the powder was heat treated in a dynamic CH4 atmosphere in previously optimized conditions (temperature: 950 °C, gas flow rate:15 cc min−1 and time: 30 min), and finally, re-calcined in various temperatures from 200 to 1200 °C. By investigating the hysteresis loops, we found the transition temperature of soft to hard magnetic behavior to be 700 °C. The maximum ratio Mr/Ms was obtained at temperatures of 800–1100 °C. At 1100 °C, and despite the Sr-hexaferrite single phase, the magnetic behavior showed a multiphase behavior that was demonstrated by a kink in the hysteresis loop. Uniform magnetic behavior was observed only at 900 °C and 1000 °C. Although the ratio Mr/Ms was almost the same at these temperatures, the values of Mr and Ms at 1000 °C were almost double of 900 °C. At 1000 °C, the second quadrant of hysteresis curve had the maximum area. Therefore, 1000 °C was the optimum temperature for re-calcination after CH4 gas heat treatment in the optimized conditions. Due to the presence of a small amount of hematite soft phase at 1000 °C, the most probable reason for the exclusive properties of the optimized product may be the exchange coupling phenomenon between the hard Sr-hexaferrite phase and the impurity of the soft hematite phase. [ABSTRACT FROM AUTHOR]

The primary focus of this research is to explore the magnetic coupling capabilities of BaFe 12 O 19 /ZnFe 2 O 4 hard/soft composites. Barium ferrite and zinc ferrite nanoparticles were fabricated using sol-gel and hydrothermal methods, respectively. The BaFe 12 O 19 /ZnFe 2 O 4 composites with diverse weight ratios (1:1, 1:2, 1:3, 2:1, and 3:1) were synthesized using the solidstate reaction procedure. The confirmation of the formation of composite particle phases was done through the analysis of FTIR and XRD spectra. Examining the FESEM micrographs revealed the agglomeration of hexagonal platelet particles (hexafrite) and spherical particles (spinel ferrite). The synthesized composites indicated medium coercivity (H c), and saturation magnetization (M s). The presence of hysteresis loops displaying a "bee waist" appearance or a stepped curve, as well as a M r ⁄M s ratio less than 0.5, shows a feeble exchange coupling between the soft and hard phases. Moreover, the switching field distribution (SFD) diagrams were analyzed to better understand the exchange coupling behavior. It was observed that all samples exhibited three distinct peaks in the dM/dH vs. H curves, which signifies a weak exchange coupling behavior between two phases of the synthesized composite. The combination of hard and soft ferrite in the right proportions increases their magnetic properties and makes it possible to achieve their properties at the same time. [Display omitted] • The hard/soft composites were synthesized through solid-state reaction method. • The synthesized composites were confirmed by FTIR and XRD detection methods. • The exchange coupling interaction of the synthesized composites were investigated. [ABSTRACT FROM AUTHOR]

The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions.

The exchange coupling, represented by the J parameter, is of tremendous importance in understanding the reactivity and magnetic behavior of open-shell molecular systems. In the past, it was the subject of theoretical investigations, but these studies are mostly limited to the interaction between metallic centers. The exchange coupling between paramagnetic metal ions and radical ligands has hitherto received scant attention in theoretical studies, and thus the understanding of the factors governing this interaction is lacking. In this paper, we use DFT, CASSCF, CASSCF/NEVPT2, and DDCI3 methods to provide insight into exchange interaction in semiquinonato copper(II) complexes. Our primary objective is to identify structural features that affect this magnetic interaction. We demonstrate that the magnetic character of Cu(II)-semiquinone complexes are mainly determined by the relative position of the semiquinone ligand to the Cu(II) ion. The results can support the experimental interpretation of magnetic data for similar systems and can be used for the in-silico design of magnetic complexes with radical ligands. [ABSTRACT FROM AUTHOR]

In this study, SrFe12O19@MFe2O4 (M = Co, Ni, Zn) core–shell nanofibers were fabricated by coaxial electrostatic spinning. The composites obtained at an annealing temperature of 900 °C are composed of SrFe12O19 in pure phase and MFe2O4 (M = Co, Ni, Zn) in different spinels. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) were used to describe the structure and morphology of nanofibers. Magnetic Property Measurement Systems (MPMS) are used to characterize the magnetic properties of nanofibers. Sr@Ni and Sr@Zn fibers all exhibit a unique core–shell structure, while Sr@Co fibers are connected by a lamellar structure. The single-phase hysteresis lines for each composite indicate the presence of exchange coupling effects between the hard/soft magnetic composite phases. The magnetic properties of the composites change as the soft magnetic material in the shell layer changes. Sr@Co has the highest Ms (69.43 emu/g) and Mr (33.82 emu/g), whereas Sr@Zn has the highest Hc (2927 Oe). The switching plant curves indicate that the best exchange coupling of the three groups of samples is for Sr@Co. The magnetic properties of the composites are explained in terms of the nanofiber diameter, the exchange coupling between the two phases, and the nature of the soft magnetic phase itself. It is shown that the exchange coupling of composites is closely related to the type of composite. [ABSTRACT FROM AUTHOR]

Band structure and topology of magneto-spin–orbit graphene is investigated using the proposed tight-binding model that incorporates both Rashba and sublattice-resolved collinear exchange couplings in a generic ferrimagnetic (FIM) setting for in-plane and out-of-plane magnetization directions. The resulting band structures were analyzed for possibilities to extract the strengths of exchange and Rashba couplings from experimental spin-resolved ARPES measurements of the valley gaps and π -state spin-splittings. It was shown that the topologically trivial in-plane FIM situation admits simple expressions for these quantities, whereas the out-of-plane FIM, which admits a nontrivial band topology, is harder to analyze. The obtained topological phase diagrams for the out-of-plane FIM case show that the anomalous Hall conductance is quite stable with respect to the antiferromagnetic (AFM) interaction, which tends to interfere with the QAHE phase; moreover, the topological phase transition has a rather smooth character with respect to the AFM coupling strength. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) magnets provide novel opportunities for understanding magnetism and investigating spin related phenomena in several atomic thickness. Multiple features of 2D magnets, such as critical temperatures, magnetoelectric/magneto-optic responses, and spin configurations, depend on the basic magnetic terms that describe various spins interactions and cooperatively determine the spin Hamiltonian of studied systems. In this review, we present a comprehensive survey of three types of basic terms, including magnetic anisotropy that is intimately related with long-range magnetic order, exchange coupling that normally dominates the spin interactions, and Dzyaloshinskii—Moriya interaction (DMI) that favors the noncollinear spin configurations, from the theoretical aspect. We introduce not only the physical features and origin of these crucial terms in 2D magnets but also many correlated phenomena, which may lead to the advance of 2D spintronics. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate the synthesis of sandwiched composite nanomagnets, which consist of hard magnetic Cr-substituted hexaferrite cores and magnetite outer layers. The hexaferrite plate-like nanoparticles, with average dimensions of 36.3 nm × 5.2 nm, were prepared via a glass crystallization method and were covered by spinel-type iron oxide via thermal decomposition of iron acetylacetonate in a hexadecane solution. The hexaferrite nanoplates act as seeds for the epitaxial growth of the magnetite, which results in uniform continuous outer layers on both sides. The thickness of the layers can be adjusted by controlling the concentration of metal ions. In this way, layers with an average thickness of 3.7 and 4.9 nm were obtained. Due to an atomically smooth interface, the magnetic composites demonstrate the exchange coupling effect, acting as single phases during remagnetization. The developed approach can be applied to any spinel-type material with matching lattice parameters and opens the way to expand the performance of hexaferrite nanomagnets due to a combination of various functional properties. [ABSTRACT FROM AUTHOR]

Gd/MgO/Fe superlattice-based nanostructures are an artificial ferromagnetic material, in which the exchange coupling of the magnetic moments of Fe layers through dielectric and rare-earth interlayers can create magnetic configurations atypical of the well-studied Fe/Cr and Fe/MgO/Fe systems. In this work, the structural features and magnetic properties of a series of Nb(20 nm)/[Gd(5 nm)/MgO(t nm)/Fe(5 nm)]х6/Nb(5 nm) superlattices with MgO dielectric layers of different thicknesses (t = 0, 0.4, 0.8, and 1.2 nm) are examined. Using high-resolution X-ray reflectometry, the formation of a layered structure of superlattices with layer thicknesses close to nominal and a root-mean-square interface roughness of 10% of the total layer thickness is established. Using vibrating-sample magnetometry, a difference between the hysteresis loops of the magnetization of a sample without a MgO layer and samples with MgO layers of different thicknesses is revealed. It is found that the sample without dielectric layers has a significantly lower saturation magnetization. [ABSTRACT FROM AUTHOR]

Valley-spin hall (VSH) effect in monolayer WSe2 has been shown to exhibit highly beneficial features for nonvolatile memory (NVM) design. Key advantages of VSH-based magnetic random access memory (VSH-MRAM) over spin orbit torque (SOT)-MRAM include access transistor-less compact bit-cell and low-power switching of perpendicular magnetic anisotropy (PMA) magnets. Nevertheless, large device resistance in the read path ( $R_{S}$ ) due to low mobility of WSe2 and Schottky contacts deteriorates sense margin (SM), offsetting the benefits of VSH-MRAM. To address this limitation, we propose another flavor of VSH-MRAM that (while inheriting most of the benefits of VSH-MRAM) achieves lower $R_{S}$ in the read path by electrically isolating the read and write terminals. This is enabled by coupling VSH with electrically isolated but magnetically coupled PMA magnets via interlayer exchange coupling. Designing the proposed devices using object-oriented micromagnetic framework (OOMMF) simulation, we ensure the robustness of the exchange-coupled PMA system under process variations. To maintain a compact memory footprint, we share the read access transistor across multiple bit-cells. Compared with the existing VSH-MRAMs, our design achieves 39%–42% and 36%–46% reduction in read time and energy, respectively, along with $1.1\times - 1.3\times $ larger SM at a comparable area. This comes at the cost of $1.7\times $ and $2.0\times $ increase in write time and energy, respectively. Thus, the proposed design is suitable for applications in which reads are more dominant than writes.

Development of high-performance permanent magnets relies on both the main-phase compound with superior intrinsic magnetic properties and the microstructure effect for the prevention of magnetization reversal. In this article, the microstructure effect is discussed by focusing on the interface between the main phase and an intergranular phase and on the intergranular phase itself. First, surfaces of main-phase grains are considered, where a general trend in the surface termination and its origin are discussed. Next, microstructure interfaces in SmFe12-based magnets are discussed, where magnetic decoupling between SmFe12 grains is found for the SmCu subphase. Finally, general insights into finite-temperature magnetism are discussed with emphasis on the feedback effect from magnetism-dependent phonons on magnetism, which is followed by explanations on atomic arrangements and magnetism of intergranular phases in Nd-Fe-B magnets. Both amorphous and candidate crystalline structures of Nd-Fe alloys are considered. The addition of Cu and Ga to Nd-Fe alloys is demonstrated to be effective in decreasing the Curie temperature of the intergranular phase.

The involvement of spin symmetry in the evaluation of zero-field energy levels in polynuclear transition metal and lanthanide complexes facilitates the division of the large-scale Hamiltonian matrix referring to isotropic exchange. This method is based on the use of an irreducible tensor approach. This allows for the fitting of the experimental data of magnetic susceptibility and magnetization in a reasonable time for relatively large clusters for any coupling path. Several examples represented by catena-[AN} and cyclo-[AN] systems were modeled. Magnetic data for 20 actually existing endohedral clusters were analyzed and interpreted.

Permanent magnets of varying shapes and sizes are increasingly produced. For hexaferrite magnets, it is challenging to incorporate polymers and a soft magnetic phase in the form of paste before injection molding or extrusion free-forming. In this study, hard magnetic barium hexaferrite/soft magnetic iron composites with a density of 2.28–2.34 g/cm3 are obtained after paste-injection molding and subsequent sintering at 1150 °C for 5 h. Variations of the binder (143.5–287.0 mg poly(vinyl alcohol), PVA) and the plasticizer (75–150 mg poly(ethylene glycol), PEG-400) in the ceramic–polymer paste give rise to comparable remanent magnetization (33.10–33.63 emu/g) and coercivity (3854–3857 Oe). Unlike all-ferrite systems, the presence of a soft magnetic metal phase is not detrimental to the coercivity. However, the remanent and saturation magnetizations are not substantially increased. The addition of 1% and 5% of iron oxide in the ceramic–polymer paste gives rise to hard/soft composites with lower densities of 2.11 and 2.14 g/cm3. The coercivity is increased to 3942–3945 Oe; however, the maximum energy product is reduced. [ABSTRACT FROM AUTHOR]

The extremely important permanent magnets encounter uncertainty and cost variations due to utilization of rare earths as prime components. Hence, the exchange coupled magnets comprised of hard and soft magnets in different proportions are explored to optimize the magnetic properties and cost. In this line, we prepared exchange coupled magnets of MnBi with FeNi@C nanoparticles (varying compositions = 10, 15 and 20 wt %) via cryogenic ball milling route. Out of these, the nanocomposite with MnBi and 15 wt% FeNi@C provided a coercivity value of 7.9 kOe with saturation magnetization and remanance values of 63 and 38 emu/g respectively. This exchange coupled magnet shown improvement in the M S , H C and M r values by 53, 18 and 90 % respectively as compared to MnBi alone. The carbon layer over FeNi@C phase (MS = 147 emu/g) as well as cryomilling facilitated the formation of its exchange coupled magnet with MnBi. [ABSTRACT FROM AUTHOR]

We report herein, emergence of photocatalytic action in Li doped two-dimensional nanosheet of graphitic carbon nitride [g-C 4 N 3 @Li n = 0-4 ]. Doping concentration varied from 3.57 % to 14.28 %. Pristine graphitic carbon nitride is half metallic and at the highest level of doping (14.28 %) it transforms into an insulating system. Observed results have been examined through the estimation of coupling between magnetic centers and the overall magnetic moment of the system. The exchange coupling (J AB) within Heisenberg–Dirac–van Vleck Hamiltonian being negative indicates antiferromagnetic coupling in presence of Li, doping. Related optical spectrum quite clearly illustrates that only at the doping level [14.28 %] the absorption peak is in the optical region. Band structure obtained illustrates a band gap of 1.92 eV and 1.93 eV in both spin channels and both oxidation and reduction potential falls within the band gap. The presence of reduction potential below the conduction band and oxidation potential above the valence band clearly illustrates the possibility of photocatalytic action. • A green sustainable solution to the problem of ongoing energy crisis is splitting of water through photocatalysis using suitable semiconducting system We report here photocatalytic activity of g-C 4 N 3 @Li 4 • Pristine graphitic carbon nitride is half metallic and at the highest level of doping (14.28 %) it transforms into an insulating system. Clear evidence of absorption peak within the visible spectra implies photocatalytic device through the absorption of visible light. • Relative position of the oxidation and reduction potential within the band gap (1.92 eV and 1.93 eV in both spin channels) of g-C 4 N 3 @Li 4 quite clearly emphasizes the possibility of splitting of water and creation of storable, transportable H2 and probable use in fuel cell. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hard/soft magnetic nanocomposites were synthesized by one pot in situ Sol-gel approach with percentages of Sn. • The synthesized nanocomposites were characterized by XRD, VSM, and microwave. • Structural analysis confirms the presence of two phases independently in the composites. • All the prepared nanocomposites exhibit single-step hysteresis loops. Magnetic nanocomposites (NCs) consisting of Sn substituted Ba/Sr hexaferrite (HFs) and cobalt ferrite as the hard (H) and the soft (S) phases respectively, H/S Sr 0.5 Ba 0.5 Sn x Fe 12- x O 19 /CoFe 2 O 4 (x ≤ 0.06) NCs (H/S Sr 0.5 Ba 0.5 Sn x Fe 12- x O 19 /CFO (x ≤ 0.06) NCs), were formed via one pot in situ Sol-gel approach using Citric acid as fuel. After that solid product was calcinated at 900 °C for 3 h. XRD analysis and Rietveld refinement confirmed the formation of desired products with the absence of any impurity. Electron microscopy (Transmission and Scanning) techniques (SEM along EDX, TEM and HR-TEM) proved the existence of both cubic and hexagonal morphology and their chemical compositions. The diverse NCs exhibited ferrimagnetic behavior at both room (RT) and low temperatures. M−H results reveal the presence of kinks in their hysteresis loops, reflecting that the exchange coupling effect was not accomplished. The M s , M r and H c values increase as the Sn content increases. Then, they start to decrease for higher Sn content. It is evident that the Sn doping in the studied H/S NCs is helpful to intensify the degree of exchange coupling effect over the dipolar interactions. Microwave characteristics of the H/S Sr 0.5 Ba 0.5 Sn x Fe 12- x O 19 /CFO NCs were explored in the range 8–12 GHz. Frequency dispersions of the real/imaginary parts of permeability and permittivity were determined from S11-S21 parameters. RL coefficient demonstrated intensive electromagnetic absorption with average level −8...-13 dB in this frequency range that corresponded to the absorption of the natural media. RL coefficient demonstrated intensive electromagnetic absorption with average level −8...-13 dB in this frequency range that corresponded to the absorption of the natural media. [ABSTRACT FROM AUTHOR]

• Spin 1/2 Heisenberg antiferromagnetic order is observed in Gd3+-based nanoparticles. • Susceptibility data agrees with theory confirming antiferromagnetic coupling. • The Néel temperature is T N ∼ 17 K. • Constriction in the MH curves is presumably due to the antiferromagnetic coupling. We report observations of spin 1 2 Heisenberg antiferromagnetic order in nanoparticle ensembles of G d 1.89 N i 0.02 Z n 0.03 F e 0.55 O 4 and G d 1.39 N i 0.10 Z n 0.02 F e 0.89 O 4. The staggered molar susceptibility, χ m (T) , of the ensembles varies as 1 / T as T → T N ≈ 17 K. Below T N , the χ m T is directly proportional to the temperature before showing another upturn. An excellent agreement between the experimental χ m (T) and theoretical models (Bonner-Fisher and Eggert) confirms spin 1 2 antiferromagnetic coupling within the linear chains of electron spins of the ensembles. The exchange constant is J k B = 17 K. The antiferromagnetic exchange interaction is also signified by a constriction at the middle of the hysteresis loop, at H = 0 , which becomes narrow at 5 K. We argue that the origin of the exchange interaction is in the quantum interference of the Bloch waves with the composite energy states of the domain walls. [ABSTRACT FROM AUTHOR]

Magnetic properties of amorphous Gd-Co ferrimagnetic films prepared by magnetron sputtering have been studied for various thicknesses. In a certain temperature range close to the magnetic compensation temperature, triple hysteresis loops and the characteristic features of the tempera-ture dependencies of magnetization were observed for all samples under consideration. Two-layer film model with an inhomogeneous chemical composition and a spin-flop transition scenario in two sub-lattice ferrimagnet was employed for understanding the origins of these phenomena. Within the framework of the spin-flop transition, the inter sub-lattice exchange coupling constant was estimated using various methods. [ABSTRACT FROM AUTHOR]

• Hard/soft magnetic composites were synthesized by physical mixing with different weight percentages. • The synthesized composites were characterized by X-ray diffraction, SQUID Magnetometer, and electrochemical impedance analyzer. • Structural analysis confirms the presence of two phases independently in the composites. • All the prepared composites exhibit single-step hysteresis loops. In this work, Strontium hexaferrite (S r F e 12 O 19) and Cobalt ferrite (C o F e 2 O 4) nanoparticles and their composites (100 − x) S r F e 12 O 19 /x C o F e 2 O 4 were synthesized. X-ray diffraction (XRD), Raman analysis and Fourier transform infrared spectroscopy, were used to investigate the structural properties of the prepared composites. XRD pattern and Rietveld refinement confirm the formation of independent phases, without any secondary phase. Scanning electron microscopy with Energy-Dispersive X-ray spectroscopy were employed to study the morphological characteristic and compositional analysis. The analysis of dielectric behavior was performed over a wide range of temperatures and frequencies, exhibiting increase in dielectric constant in the composite. Magnetic properties have been studied at room temperature by measuring the magnetic hysteresis loop. Hard phased Strontium hexaferrite exhibited a large coercivity of 5.9 kOe, whereas soft phase cobalt ferrite shows a saturation magnetization value of 78.4 emu/g. The law of approach to saturation magnetization is applied for the estimation of magnetic saturation in all the composites and observed to vary from 71.3 emu/g to 72.9 emu/g. All the magnetic composites exhibit single-phase magnetic loops confirming, the exchange coupling in all prepared composites. The presence of exchange coupling in hard/soft composites was studied using d M d H vs H plot. [Display omitted] [ABSTRACT FROM AUTHOR]