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Permanent magnets generate magnetic fields that can be sustained when a reverse field is supplied. These permanent magnets are effective in a wide range of applications. However, strategic rare-earth element demand has increased interest in replacing them with huge energy product (BH) max . Exchange-coupled hard/soft ferrite nanocomposites have the potential to replace a portion of extravagant rare earth element-based magnets. In the present, we have reported the facile auto combustion synthesis of exchange-coupled Ba 0.5 Sr 0.5 Fe 10 Al 2 O 19 and Ni 0.1 Co 0.9 Fe 2 O 4 nanocomposites by increasing the content of soft ferrite over the hard from x = 0.1 to 0.4 wt%. The XRD combined with Rietveld analysis reflected the presence of hexaferrite and spinel ferrite without the existence of secondary phases. The absorption bands from the Fourier transform infrared spectrum analysis proved the presence of M-O bonds in tetrahedral sites and octahedral sites. Rod and non-spherical images from TEM represent the hexaferrite and spinel ferrite. The smooth M - H curve and a single peak of the switching field distribution curve prove that the material has undergone a good exchange coupling. The nanopowders displayed an increase in saturation magnetization and a decrease in coercivity with the increases in the spinel content. The prepared nanocomposites were showing higher energy products. The composite with the ratio x = 0.2 displayed a higher value of (BH) max of 13.16 kJ m -3 ., (© 2024 IOP Publishing Ltd.)

Phase constituents, microstructures and magnetic properties of melt-spun Nd12−xYxFe81B6Nb ribbons were investigated systematically. The influence of Y substitution for Nd on the phase stability, grain size and magnetic exchange coupling was analyzed. It is found that all the ribbons crystallize in the tetragonal 2:14:1 structure, i.e., with single hard magnetic phase at the roll speed of 25 m·s−1. With the increase in Y doping, Curie temperature (TC) increases, while the coercivity decreases monoclinically. However, remanence magnetization (Br) and maximum energy product ((BH)max) fluctuate and the maximum value is obtained at certain amount of Y. The optimum magnetic properties of intrinsic coercivity of intrinsic coercivity (Hcj) = 908.2 kA·m−1 and (BH)max = 118.52 kJ·m−3 are achieved when x = 1.0. It can be attributed to the strengthened exchange coupling between the neighboring nanograins in Nd–Y–Fe–B melt-spun powder based on the Henkel curves. Furthermore, Y substitution also significantly improves the temperature stability of magnetic performance. The coercivity temperature coefficient of β = − 0.157%·°C−1 and remanence temperature coefficient of α = − 0.32%·°C−1 are gained, which are greatly reduced compared with those of the undoped Nd–Fe–B compounds. [ABSTRACT FROM AUTHOR]

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• Magnetic nanoflowers of MnFe 2 O 4 (as seed) and γ-Fe 2 O 3 were successfully synthesised. • Three-fold increase in the ILP values for nanoflowers than single-core MNPs. • The nanoflowers were found to be biocompatible even at higher concentrations ∼3 mg/mL. • Magnetic hyperthermia with 0.75 mg/mL of nanoflowers decreased HeLa cells viability to 17%. Magnetic materials with high specific loss power (SLP) are desirable for magnetic hyperthermia to minimise the amount of material required to obtain the therapeutic temperature (42–46 °C) to destroy the cancer cells. The exchange coupled core-shell structure and the nanoclusters of magnetic nanoparticles having high SLP values are the most suitable candidates for this purpose. Herein, a simple method has been demonstrated for the synthesis of exchange coupled magnetic nanoflowers consisting of γ-Fe 2 O 3 magnetic grains grown over the surface of MnFe 2 O 4 core. The aqueous ferrofluid of nanoflowers displayed higher SLP values than single phase MnFe 2 O 4 core. The intrinsic loss parameter for the nanoflowers was 3.30 nH m2 Kg−1 at an applied magnetic field of amplitude 250 Oe and frequency 113 kHz, which was significantly higher than the commercially available ferrofluids. The cytotoxicity of the nanoflowers were studied with HeLa cells. The magnetic hyperthermia treatment for 30 min with 0.75 mg/mL ferrofluid of the nanoflowers demonstrated a temperature rise to 46 °C and decreased the cell viability to 17% for HeLa cells. These nanoflowers (size around 40–60 nm) showed better magnetic properties viz. higher saturation magnetisation, initial susceptibility and lower coercivity, making them a suitable candidate for biomedical applications. [ABSTRACT FROM AUTHOR]

• CFO thin films were transformed to CFO/Co-Fe hard/soft nanocomposite films by annealing in hydrogen atmosphere. • The two phases CFO and Co-Fe solid solution was controlled by the annealing time. • The magnetization increases, by increasing hydrogen annealing time. • X-ray photoelectron spectroscopy was determined the formation of soft phases in the CFO films. Pulse laser deposited cobalt ferrite CoFe 2 O 4 (CFO) thin films were transformed to CFO/Co-Fe solid solution hard/soft nanocomposite thin films by annealing the CFO films in hydrogen atmosphere. By controlling the annealing time, the level of transformation between the two phases was controlled thereby the exchange coupling and magnetic properties of the nanocomposite layer. X-ray diffraction patterns showed the formation of (0 0 l) orientation for the CFO hard phase and (0 l l) orientation for bcc Co-Fe solid solution soft phase in all samples. Atomic force microscopy images revealed that by increasing the annealing time, the surface roughness of the films increased. Magnetic measurements demonstrate that the more the annealing time, the higher the saturation magnetization and the lower their coercivity and magnetic anisotropy. Hysteresis loops of the films show that these samples behave like single-phase materials indicating the presence of exchange coupling between two different hard and soft phases. Using X-ray photoelectron spectroscopy (XPS), we determined the cations distribution variation in our samples thus a change in the spinel inversion parameter (y) from 0.70 for the as-deposited CFO to 0.49 for the films reduced in hydrogen for 60 min. The Raman spectroscopy confirms the XPS results in our samples. The present approach may help the development of methods for tuning the saturation magnetization, coercivity and magnetic easy axis direction in magnetic nanocomposite thin films and magnetic oxide-based spintronic devices. [ABSTRACT FROM AUTHOR]

The BaFe 12 O 19 particles were synthesized by co-precipitation and calcination. Fe 5 C 2 nanoparticles were synthesized in an organic solvent. The BaFe 12 O 19 and Fe 5 C 2 particles were mixed through cryogenic ball milling. The elemental mappings indicated that two crystal phases were homogenously mixed after the milling, and the magnetic properties of BaFe 12 O 19 /Fe 5 C 2 composites were investigated by VSM. When the mass percentage of Fe 5 C 2 was 10%, the composite presented the optimum magnetic exchange coupling in BaFe 12 O 19 /Fe 5 C 2 composites and the largest (BH) max (31% increase from pure BaFe 12 O 19). As a comparison, the room temperature ball milled BaFe 12 O 19 /Fe 5 C 2 showed less exchange coupling compared with cryogenic ball milling counterpart. Finally, the air stability of BaFe 12 O 19 /Fe 5 C 2 composite was also investigated. [ABSTRACT FROM AUTHOR]

A trilayer magnetoelectric (ME) YIG/Terfenol-D/PZT structure (YTP) with a high ME coefficient is proposed. The enhanced ME effect of YTP comes mainly from the exchange coupling action in YIG/Terfenol-D bilayers (YT) and the ME effect in Terfenol-D/PZT bilayers (TP). The multi-physics coupling action among electric field, magnetic field and mechanical stress field is a novel way to enhance the ME effect of YTP. The exchange coupling action of YT is analyzed by the minimum free energy principle, and the relationship between the magnetization M 1 of the YIG layer and the M 2 of the Terfenol-D layer is obtained. The prominent ME effect was achieved in YTP, and the magnetization angle of the YIG layer rotated 40°·cm/kV. In an YTP microstrip filter, the exchange coupled effective field H ex and the stress effective field H σ affect the ferromagnetic resonance (FMR) frequency shift Δω, which can reach 300 MHz · cm/kV at an electric field of 8 kV/cm and a bias magnetic field of 1700 Oe. The excellent electric tunability of YTP makes it a promising candidate of the electric and magnetic field dual-tunable microstrip filter. • A trilayer ME YIG/Terfenol-D/PZT structure is proposed. • The microwave ME effect is enhanced due to the exchange coupling in YIG/Terfenol-D and the ME effect in Terfenol-D/PZT. • The YIG/Terfenol-D/PZT microstrip filter shows excellent electric tunability of FMR frequency shift of 300 MHz·cm/kV. [ABSTRACT FROM AUTHOR]

• Coercivity increases significantly in Nd 12.2 Fe 81.8 B 6 sintered magnets by mixing Tb 17 Fe 75 B 8 powders. • The effect of dual-main-phase structure on coercivity is better than that of conventional dual-alloy method. • The exchange coupling also contributes to coercivity enhancement in Nd-Fe-B/Tb-Fe-B magnets. Nd 12.2 Fe 81.8 B 6 and Tb 17 Fe 75 B 8 powders were mixed to prepare sintered magnets by the powders preparation, pressing and sintering. With a small addition of Tb 17 Fe 75 B 8 powders the coercivity increases largely in the Nd-Fe-B/Tb-Fe-B magnets. For the addition of 0.5 g Tb 17 Fe 75 B 8 (the mass ratio 0.5:9.5 of Tb 17 Fe 75 B 8 and Nd 12.2 Fe 81.8 B 6), the coercivity increases to 15.8 kOe, 2.2 times of that in Nd 12.2 Fe 81.8 B 6. With more amount addition of Tb 17 Fe 75 B 8 powders the coercivity keeps to increase, and the increase is larger than that of the conventional dual-alloy method. The magnets consist of two main phases, but the atomic interdiffusion is evident for Nd and Tb. Via the investigation of thermal activation it shows that the domain walls size decreases for a little amount addition of Tb 17 Fe 75 B 8 powders. So the magnetocrystalline anisotropy increases near grain boundary of Nd-Fe-B phase owing to Tb diffusing and substituting for Nd, which is beneficial to the enhancement of coercivity. For the addition of Tb 17 Fe 75 B 8 more than 0.7 g the domain wall size doesn't decrease evidently, suggesting that the existing of interfacial exchange coupling which also contributes to the increase of coercivity in the sintered composite magnets. [ABSTRACT FROM AUTHOR]

The magnetoelectric coupling mechanism in Ni/BiFe 0.95 Mn 0.05 O 3 heterostructures is investigated through a detailed microstructural study of the BiFe 0.95 Mn 0.05 O 3 film and a chemical analysis of the Ni/BiFe 0.95 Mn 0.05 O 3 interface. The four structural variants expected in BiFe0.95Mn0.05O3 are detected by high resolution X-ray diffraction reciprocal space mapping method. The ferroelectric domain structure is imaged with transmission electron microscopy. Oxidized Ni is evidenced at the Ni/BiFe 0.95 Mn 0.05 O 3 interface by electron energy loss spectroscopy and X-ray photoemission spectroscopy, although the degree of Ni oxidation is independent of the magnetoelectric state of the heterostructure. • Strong magneto-electric coupling effect is demonstrated in Ni/BiFe 0.95 Mn 0.05 O 3 heterostructures. • The origin of the coupling mechanism is studied through detailed structural and chemical investigations. • XRD and TEM crystallographic analysis reveal the ferroelectric structure of the BiFe 0.95 Mn 0.5 O 3 film. • EELS and XPS measurements at the Ni/BiFe 0.95 Mn 0.05 O 3 interface explore electrochemical effects. [ABSTRACT FROM AUTHOR]

Abstract The interlayer plays a crucial role in improving the properties of many extremely important magnetic materials and devices by regulating the magnetic exchange coupling, while it is still not fully understood in a quantitative way. The main obstacle is that there is still no effective way to characterize quantitatively the ferromagnetic exchange coupling (FEC) strength after inserting the interlayer. In this paper, a rationally designed hard/interlayer/soft layered film is used to study the interlayer effects. It is demonstrated that the magnetic properties of nanocomposite magnets can be effectively enhanced through the modification of interface. Here a new concept, using the nucleation field H ns of soft phase as a "detector" to directly and quantitatively characterize/measure the FEC strength across interface and interlayer, is put forward. It is applied to address the dependence of FEC strength on thickness of nonmagnetic Cr and rare earth-rich phase interlayers. The detailed, distinguishing and typical decay behavior and length of FEC strength for these interlayers are successfully resolved for the first time. The new conception and experimental results get also strongly supported by the theoretical calculation. The nature or mechanism of exchange coupling between ferromagnetic grains or layers after adding the nonmagnetic interlayer is identified by using the hard/interlayer/soft layered film as a model system. Our results demonstrate the validity for characterizing/measuring quantitatively the FEC strength across different interlayer materials via strategy established in this work. It opens up new perspectives to gain insight into the interlayer property, and mechanism comprehension and high-performance design for magnetic materials and devices, such as permanent magnets, high-density magnetic recording media, advanced spin-orbit torque devices, etc. Highlights • The interface layer (interlayer) plays a crucial role in improving the properties of many important magnetic materials and devices by regulating the ferromagnetic exchange coupling (FEC), while it is still not fully understood. The main obstacle is that there is no effective way to quantitatively characterize the FEC strength across the interlayer. • In this paper, a new conception, using the nucleation field Hns of soft phase in a rationally designed hard/interlayer/soft layered film to directly characterize/measure the FEC strength across the interlayer(or interface), is put forward. • It is applied to address the dependence of FEC strength on thickness of nonmagnetic Cr and rare earth-rich phase interlayers. The detailed, distinguishing and typical decay behavior and length of FEC strength are successfully resolved. The new conception and experimental results get strongly supported by theoretical calculation. • The nature or mechanism of exchange coupling between ferromagnetic grains or layers after adding the nonmagnetic interlayer is also identified by using the hard/interlayer/soft layered film as a model system. • Our results open up new perspectives to gain insight into the interlayer property, and mechanism comprehension and high-performance design for magnetic materials and devices, such as permanent magnets, magnetic recording media, advanced spin-orbit torque devices, etc. [ABSTRACT FROM AUTHOR]

Highlights • Partial decomposition of SrAl 2 M hexaferrite in Ar/H 2 atmosphere. • Formation of SrAl 2 M/FeCo 2 nanocomposites through reduction of CoFe 2 O 4. • Formation of SrAl 2 M/Fe nanocomposites through borohydride reaction. • Hysteresis behavior of nanocomposites shows absence of exchange coupling. Abstract Hard/soft magnetic nanocomposites were synthesized with SrAl 2 Fe 10 O 9 as hard and CoFe 2 or Fe as soft magnetic phase. Al-substituted hexaferrite powder with 250 nm particle size is stable in Ar/5%H 2 atmosphere at 315 °C, contrary to non-substituted hexaferrite. Annealing at T > 400 °C under these conditions leads to formation of Fe metal besides remaining hexaferrite phase. Such nanocomposites exhibit hysteresis loops with increased M s. Alternative routes to synthesize nanocomposites were also explored. A mixture of hexaferrite and nanosize CoFe 2 O 4 particles was annealed at 315 °C in Ar/5%H 2 atmosphere. The spinel ferrite particles were reduced to CoFe 2 alloy. Alternatively, soft iron nanoparticles were deposited onto the Al-substituted hexaferrite particles via a sodium borohydride reaction. Annealing at 315 °C in Ar/5%H 2 gives a hexaferrite/Fe composite powder. Room temperature hysteresis loops, however, exhibit a multiple-phase reversal behavior. [ABSTRACT FROM AUTHOR]

In this work, we present a detailed magneto-optical Kerr effect (MOKE) study of amorphous FeCoB (FCB)/MgO bilayer grown on Si (100) substrate. Two regions with different boron density has been identified in single FCB layer in the as-deposited bilayer due to boron diffusion from FCB to MgO layer at the interface: (i) a boron-deficient layer near FCB/MgO interface (FCBi) and (ii) bulk FeCoB layer (FCBb) located farther away from FCB/MgO interface and having comparatively high boron concentration. As a result, a stress-induced uniaxial magnetic anisotropy is observed in the boron deficient FCBi layer, which is found to be superimposed with the magnetization of FCBb layer. Depending on the angle between the applied magnetic field and the uniaxial easy axis of the FCBi layer, magnetization reversal with single step or double step are observed. Role of interlayer exchange coupling between FCBi and FCBb layer is determined by separating out their magnetic contributions by fitting hysteresis loops with a mathematical function. The disappearance of double step behavior after in-situ annealing up to 473 K, suggests that the observed magnetic anisotropy mainly originates from the strain in the film. • Unusual single step and two step magnetization reversal observed in amorphous FeCoB/MgO bilayer at room temperature. • Two layer with different boron concentration identified in single FeCoB layer due to diffusion of boron from FeCoB to MgO. • Stress induced uniaxial magnetic anisotropy observed in boron deficient layer at the interface. • Exchange coupling between above two layers give rise to unusual step hysteresis loop. [ABSTRACT FROM AUTHOR]

We investigated the electronic structure, density of states and exchange couplings, magnetic properties and magnetocaloric effect of La 0.67 Sr 0.33 MnO 3 composition by using a combination of ab initio calculations and Monte Carlo Simulation. Ab initio calculations show the stability of the ferromagnetic phase in this material. The Monte Carlo simulations combined with ab initio exchange coupling constants as input parameters lead to discuss the transition temperature, critical exponents, isothermal entropy changes, adiabatic temperature change and relative cooling power (RCP). The calculated critical temperature was T c = 358 K and the isothermal magnetic entropy changes reaches a maximum value of 3.78 J kg−1 for a field change of 5 T. The adiabatic temperature reaches a maximum value equal to 3.55 K and the RCP maximum value is found to be 210 J kg−1 for a magnetic field of 5 T, which suggest La 0.67 Sr 0.33 MnO 3 could be considered as a good candidate for magnetic refrigeration above room temperature at moderate magnetic fields. • La 0.67 Sr 0.33 MnO 3 has been studied using ab initio and Monte Carlo Simulation. • Structure optimization, density of states, exchange couplings were computed. • Magnetic properties and magnetocaloric effect were calculated. [ABSTRACT FROM AUTHOR]

The azafullerene Tb2@C79N is found to be a single‐molecule magnet with a high 100‐s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy‐axis single‐ion magnetic anisotropy are strongly coupled by the unpaired spin of the single‐electron Tb−Tb bond. Relaxation of magnetization in Tb2@C79N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τQTM=16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped. New kids on the blocking: The azafullerene Tb2@C79N featuring a single‐electron Tb−Tb bond is found to be an air‐stable single‐molecule magnet with a high 100‐s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy‐axis single‐ion magnetic anisotropy are strongly coupled by the unpaired spin of the single‐electron Tb−Tb bond. [ABSTRACT FROM AUTHOR]

Abstract Nanosize CoFe 2 O 4 particles were synthesized via thermal decomposition of a mixed oxalate precursor; the mean ferrite particle size between 5 nm and 35 nm is tailored through variations of the decomposition temperature. Ferrite particles of 22 nm and 14 nm size were subsequently heated in Ar/5%H 2 atmosphere at 315 °C for various holding times. The resulting nanocomposites consist of spinel ferrite, CoO and CoFe 2 , with the alloy concentration increasing with dwell time. Room temperature hysteresis loops exhibit a single-phase reversal behavior and remanence enhancement. An increase of the maximum energy product was observed as well. Hysteresis loops at 5 K, however, show two-phase behavior indicating that no exchange coupling is active. Highlights • Synthesis of nanosize, ferrimagnetic CoFe 2 O 4 particles. • Phase formation of ferrite/CoFe nanocomposites in argon/hydrogen atmosphere. • Single-phase hysteresis behavior and remanence enhancement at room temperature. • Magnetization behavior at 5K and Henkel plots proof absence of exchange coupling. [ABSTRACT FROM AUTHOR]

Abstract Unique rotatable anisotropy is designed and achieved in Fe 4 N thin film with quasi-single magnetic domain structure by the exchange coupling between magnetic crystalline grains. It is found that the rotatable anisotropy can be characterized with isotropic rectangular in-plane hysteresis loops with remanence ratio close to 0.9 and angle-independent permeability spectra with quasi-isotropic resonance frequency, line-width and amplitude. Strength of the rotatable anisotropy is estimated by the random anisotropy model theoretically and it is comparable with the experimental results. Its rotatable feature can be understood from the equivalent remanence state established along different directions and the nucleation magnetization reversal. Moreover, a static method is established to determine rotatable anisotropy of the Fe 4 N thin film. A 50 Oe rotatable anisotropy was determined by M - H curve measured by B - H loop analyzer, which is close to 58 Oe derived from the permeability spectra. Our work provides the new way to search and characterize the rotatable anisotropy in magnetic systems. Highlights • Unique rotatable anisotropy is achieved in Fe 4 N nanocrystalline thin film. • The rotatable anisotropy is measured experimentally and explained theoretically. • A new static method is developed to determine the unique rotatable anisotropy. [ABSTRACT FROM AUTHOR]

Highlights • The structural and magnetic properties of Mn 53.3 Al 45 C 1.7 and Fe 65 Co 35 were studied. • It can be concluded that the soft and hard particles are polycrystalline. • The magnetic exchange coupling was proved by Thamm-Hesse analysis. • MnAlC/FeCo (95/5 w.t%) sintered at 500 °C for 30 min, present a (BH) max = 5.57 kJ/m3. Abstract The τ -MnAlC/FeCo system has potential to be applied as rare earth-free permanent magnet, due to exchange coupled between hard and soft magnetic phases as alternative for the development of high energy product permanent magnets. In this work the hard-magnetic phase Mn 53.3 Al 45 C 1.7 (μ 0 H c = 0.37 T of coercive force, M r = 23.52 Am2/kg of remanent magnetization, M s = 52.94 Am2/kg of saturation magnetization and (BH) max = 3.89 kJ/m3 of maximum energy product) was mixed with the soft magnetic phase Fe 65 Co 35 (μ 0 H c = 0.007 T and M s = 221.33 Am2/kg) using a solid-state procedure. The magnetic materials were sintered using different ratios of hard and soft magnetic phases: 95:5, 90:10, 85:15 and 80:20; and different sintering temperatures (300, 400, 500 and 600 °C) in order to improve the magnetic properties. The magnetic exchange coupling between MnAlC and FeCo was proved by the hysteresis loop and its corresponding Thamm-Hesse analysis. The best result was obtained for MnAlC/FeCo (95/5 wt%) sintered at 500 °C during 30 min, for which the magnetic properties were μ 0 H c = 0.277 T, M s = 76.43 Am2/kg and (BH) max = 5.57 kJ/m3. [ABSTRACT FROM AUTHOR]

Highlights • La substitution effects have been studied for melt-spun (Nd 1− x La x) 13 Fe 81 B 6 (0 ≤ x ≤ 0.5) alloys. • An anomalous increase in J r value was observed for the alloy with x = 0.4. • This anomalous behavior is due to inhomogeneous distribution of Nd and La. • Strong exchange coupling derived from Henkel plots and the smaller average grain size are observed in the alloy with x = 0.4. • Cost effective melt-spun NdFeB magnetic alloys can be developed by La substitution for Nd. Abstract The expensive rare earth elements Nd, Pr, Dy and Tb have been extensively used for making NdFeB-based magnets, but the less expensive and high abundant rare earth (HARE) elements such as La and Ce have been over stocked. The marketing expansion of the HARE elements is of much interest in academia and industry to achieve effective and efficient utilization of HARE elements. In this paper, nanocrystalline (Nd 1− x La x) 13 Fe 81 B 6 (x = 0–0.5) alloys were fabricated by melt-spinning method. It is found out that the room temperature magnetic properties of the alloys decrease sharply when La is substituted for Nd up to 20 at.%. However, an anomalous increase in J r value and improved thermal stability of the alloy ribbons are observed for 40 at.% La substituted alloy while the reduction in magnetic properties is only nominal up to 30 at.%. Furthermore, the Curie temperature decreases from 588 K to 561 K with 50 at.% La substitution, which is higher than the equal amount of Ce substitution in Nd-Fe-B. It is shown by the Henkel curves that the alloy with 40 at.% La has the biggest value of positive peak which demonstrates the strongest exchange coupling in the 40 at.% La substituted alloy. The TEM micrographs indicate that the alloy containing 40 at.% La has more uniform and refined microstructure resulted in the enhanced properties. [ABSTRACT FROM AUTHOR]

In this study, [Co/Ni]2/PtMn thin films with different PtMn thicknesses (2.7 to 32.4 nm) were prepared on Si/SiO2 substrates. The post-deposition perpendicular magnetic field annealing (MFA) processes were carried out to modify the structures and magnetic properties. The MFA process also induced strong interlayer diffusion, rendering a less sharp interface between Co and Ni and PtMn layers. The transmission electron microscopy (TEM) lattice image analysis has shown that the films consisted of face-centered tetragonal (fct) PtMn (ordered by MFA), body-centered cubic (bcc) NiMn (due to intermixing), in addition to face-centered cubic (fcc) Co, Ni, and PtMn phases. The peak shift (2-theta from 39.9° to 40.3°) in X-ray diffraction spectra also confirmed the structural transition from fcc PtMn to fct PtMn after MFA, in agreement with those obtained by lattice images in TEM. The interdiffusion induced by MFA was also evidenced by the depth profile of X-ray photoelectron spectroscopy (XPS). Further, the magnetic properties measured by vibrating sample magnetometry (VSM) have shown an increased coercivity in MFA-treated samples. This is attributed to the presence of ordered fct PtMn, and NiMn phases exchange coupled to the ferromagnetic [Co/Ni]2 layers. The vertical shift (Mshift = −0.03 memu) of the hysteresis loops is ascribed to the pinned spins resulting from perpendicular MFA processes.

[Display omitted] • We utilize the intrinsic magnetism of CrI 3 to break the time-reversal symmetry of WTe 2 , thus inducing a giant valley splitting of up to 34.01 meV. • By modulating the interlayer exchange coupling and applying perpendicular external electric fields, a wide range of valley splitting manipulation can be achieved. • The method of magnetic ion intercalation, particularly the self-intercalated Cr ion, significantly enhances the valley splitting by an order of magnitude. • The method of magnetic ion intercalation, particularly the self-intercalated Cr ion, can significantly enhance the valley splitting of WTe 2 /CrI 3 heterostructure by an order of magnitude. Lifting the valley degeneracy is an essential condition for exploiting the valley degrees of freedom to process and store information in valleytronics. The magnetic proximity effect (MPE) has been proven to be an effective method for introducing a magnetic field via interlayer exchange interaction, which can be conveniently achieved by two-dimensional (2D) van der Waals (vdW) heterostructure engineering. We have investigated the electronic properties and valley physics of 2D WTe 2 /CrI 3 heterostructure using first-principles calculations. The results show that a significant valley splitting of 34.01 meV can be obtained in the WTe 2 /CrI 3 heterostructure due to the simultaneous breaking of inversion and time-reversal symmetry, which sensitively depends on the atomic overlap of the projected position in the specific stacking model. In addition, we also show that the valley splitting can be enhanced by applying a vertical external electric field (E-field) or reducing the interlayer distance. More than that, it can be boosted by an order of magnitude (∼115.25 meV) through Cr ion intercalation. This is attributed to that the self-intercalated Cr ion has ferromagnetic (FM) ordering and perpendicular magnetic anisotropy due to the exchange coupling of the CrI 3 layer. This result provides fundamental insights and valuable guidance for the application of 2D WTe 2 /CrI 3 heterostructure in novel spintronic and valleytronic devices. [ABSTRACT FROM AUTHOR]

• Proper Co content can refine the microstructure and improve the exchange coupling interaction, leading to enhance the magnetic properties. • The optimum energy product (BH) max (11.28 MGOe) is obtained with a proper Co addition at x = 1, which can get 42.9 % improvements comparing to the Co-free alloy. • The enhanced magnetic properties stem from the refinement of the 2:14:1 phase grains and the presence of uniform and smaller interaction domains. In this study, [Nd 0.5 (Ce 0.5 La 0.5) 0.5 ] 17 Fe 78- x Co x B 6 (x = 0 ∼ 1.5 at. %) ribbons are prepared via a direct melt-spun (wheel speed of 28 m/s). The impacts of Co doping on the crystal structure, Curie temperature T c , magnetic parameters (B r , H ci and (BH) max) of [Nd 0.5 (Ce 0.5 La 0.5) 0.5 ] 17 Fe 78- x Co x B 6 alloys are systematically assessed. X-ray diffraction patterns and Rietveld refinement data demonstrate that the exclusive presence of a pure hard magnetic 2:14:1 phase without any secondary phases across all samples. Compared with Co-free sample (x = 0), the B r , H ci and (BH) max of Co-doped with x = 1 are increased by 15.0 %, 4.6 % and 42.9 %, respectively. The coercivity mechanism in the [Nd 0.5 (Ce 0.5 La 0.5) 0.5 ] 17 Fe 78- x Co x B 6 alloys arises from the integration of reversed domain nucleation and robust pinning of domain walls. The magnetic domain structure and quantitative analysis based on the microstructure and demagnetization behavior are conducted to investigate the exchange coupling interactions among the 2:14:1 grains. This exploration reveals that the enhanced magnetic properties stem from the refinement of the 2:14:1 phase's grains, leading to more uniform and smaller interaction domains. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/CoO nanocomposites were prepared by a polyol method and subsequent annealing. • Annealing has led to enhancement of the exchange coupling between Co and CoO phases leading to an increase of H eb. • The dependence of H eb on the FM-AFM exchange coupling was discussed using a 1D-Heisenberg-model Monte Carlo simulation. • The simulation also underpined the experimental data on temperature dependence of the H eb and H c. In this study, Co particles were synthesized by a polyol method, and the subsequent annealing in air was performed to prepare Co/CoO nanocomposites. Samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and magnetic measurements. SEM images of a typical nanocomposite sample pointed out the agglomeration of about 20 nm particles into micrometer-sized spheres. XRD analysis showed an increased content of the CoO phase with annealing time. The main focus was given to the effect of annealing on the exchange coupling between the Co ferromagnetic phase and the CoO antiferromagnetic phase, which in turn affects the exchange bias effect (EB) in this material. It was shown that annealing enhanced the exchange coupling between two phases leading to an increase of the exchange bias field (H eb) as compared to the unannealed sample. A value of H eb = 155 Oe was attained with annealing at a temperature of 300 °C for 90 min. The dependence of H eb on the exchange coupling between phases was discussed using a 1D-Heisenberg-model Monte Carlo simulation. Besides, the simulation also underpined the experimental data on temperature dependence of the EB and coercivity. [ABSTRACT FROM AUTHOR]

• The presence of Ti suppressed the formation of α-Fe phase. • The addition of Ti promoted the generation of vortex-like magnetic domain and improve the coercivity. • The increase in coercivity can be attributed to the enhanced exchange coupling and the pinning effect of the vortex-like domain. In this work, the effect of tunable Ti content on the microstructure, magnetic domain structure, and magnetic properties of as-spun and annealed Nd 9.5 Fe 79- x Co 5 Ti x B 6.5 (x = 0,1,2,3,4) alloys at the quench speed of 18 m/s were investigated. For the as-spun alloy, augmenting the Ti content enhanced the initial crystallization temperature and the stability of the amorphous phase. Simultaneously, the incorporation of Ti led to augmentation in the quantity of nanocrystals within the amorphous matrix, thereby facilitating the formation of vortex-like magnetic domains with large size but reduced the saturation magnetization M s. For the annealed alloy, the incorporation of Ti inhibited the precipitation of α-Fe phase, refined the grain, enhanced the exchange coupling between the soft and hard magnetic phase and facilitated the formation of smaller, more uniform vortex-like magnetic domains, These alterations were beneficial to improve the comprehensive magnetic properties. Furthermore, the addition of tunable Ti resulted in a remarkable impact on coercivity enhancement. The coercivity value exhibited a significant increase of 54.30%, surging from 374.24 kA/m to 577.51 kA/m. Upon a thorough analysis of the magnetic domains and coercive force mechanisms, it was ascertained that the introduction of Ti substantially augmented the creation of vortex-like domains. These domains effectively impede domain motion, consequently elevating the material's coercivity. [ABSTRACT FROM AUTHOR]

This article studies the influence of dipole interactions on the magnetic properties. Specifically, FINEMET/SiO 2 and FINEMET/SiO 2 /Fe 20 Ni 80 composite ribbons were prepared by magnetron sputtering. During the manufacturing process, the Fe 20 Ni 80 film with a fixed thickness of 260 nm and the FINEMET ribbon were separated by the SiO 2 layer, and the SiO 2 layer thickness could be adjusted within a range of 0–150 nm. This configuration enabled the exchange coupling gradually reduced with the SiO 2 layer thickness increased, allowing dipole interactions to become the dominant factor. This study not only excludes the influence of the SiO 2 in the composite ribbons but analyzes the effect of the exchange couple and dipole interactions for the GMI, respectively. The experimental results show the GMI ratio decreases initially and then increases with the thickness of SiO 2 , where the optimization of GMI ratio was explored in FINEMET/Fe 20 Ni 80 ribbons. On the other hand, the minimum peak field was shown with the SiO 2 thickness of 5 nm. Furthermore, the results also elucidate that both dipole interactions and exchange couple have affected the peak field of GMI, which could be used for the design of multilayer composite ribbons with better performance. Thus, the analysis we showed in this work is thought to be valuable in revealing the mechanism of multilayer composite ribbons for future sensing applications. • Using GMI to distinguish exchange coupling and dipole interactions in multilayer magnetic materials. • A convenient and efficient way to study magnetic interactions. • The impacts of SiO 2 on FINEMET composite ribbons systematically analyzed. [ABSTRACT FROM AUTHOR]

With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases.

The value of exchange energy for near-surface double-donor and double-quantum dot structures under the effect of external electric field has been calculated using unrestricted Hartree–Fock method. The dependences of exchange energy on geometric parameters have been obtained. It has been found that the location of donor centers near the surface of the semiconductor leads to an increase in the exchange energy. Approximate formulas for the dependence of the exchange energy on the distance between the centers of quantum dots are suggested. It has been shown that exchange coupling control is less sensitive to electric field as compared to magnetic field, and electron density relocation at large electric fields should be taken into account when designing devices based on the structures under study. [ABSTRACT FROM AUTHOR]

Systematic investigation was made on the magnetic property of a series of Nd2Fe14B/α-Fe nanocomposites prepared by crystallization of amorphous Nd8Fe84Ti2B6 ribbon at annealing temperatures in the range of 800-860 °C. Both remanence and energy product increase with increasing annealing temperature, reaching the maximum values at 850 °C. Coercivity remains around 5.5 kOe for the annealing temperatures above 800 °C. Although the smooth demagnetization curve indicates effective exchange coupling between the Nd2Fe14B/α-Fe dual phases, FORC diagram reveals the existence of α-Fe for the Nd8Fe84Ti2B6 ribbon annealed at 850 °C. In addition, the variation of microcoercivity at different locations indicates a distributed exchange interaction, which can be caused by the nonuniform microstructure. The magnetic property is also affected by the demagnetization effect caused by the particle shape, which is evidenced by the negative region in the first-order reversal curve (FORC) diagram.

Single‐molecule magnets (SMMs) are discrete metal complexes that retain their magnetisation below a certain temperature, with possible applications in quantum information processing, molecular spintronics and high‐density data storage. Complexes of lanthanoid(III) ions have proven highly successful in the field, some exhibiting magnetic hysteresis at liquid nitrogen temperatures. Inelastic neutron scattering (INS), widely used for the study of the crystal field splitting engendered by the coordination environment of metal centres, can afford a wealth of information when applied to the study of these molecular nanomagnets, as the SMM properties arise from the electronic structure of the lanthanoid(III) ions. Although relatively underutilised to date, INS can be employed alongside crystal field analysis, and/or ab initio calculations, to understand how subtle structural changes impact SMM behaviour. In this Minireview we discuss the application of INS to the study of lanthanoid complexes, to elucidate both crystal field splitting and exchange coupling in coupled metal‐radical and metal‐metal SMMs. Lanthanoid(III) complexes constitute state‐of‐the‐art single‐molecule magnets (SMMs), exhibiting slow magnetic relaxation and magnetisation quantum tunnelling, which arise from the electronic structure of the lanthanoid(III) ion. Inelastic neutron scattering is a powerful but underutilised technique for elucidating the electronic structure that affords SMM behaviour. [ABSTRACT FROM AUTHOR]

Abstract The Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure. Phase diagrams are attained with diverse single-ion anisotropies and exchange couplings. It is discovered plentiful phase transitions in the nanowire system, for example, the compensation behaviors, the second-order and first-order phase transitions as well as the tricritical point phenomena. We have discussed the significant effects of single-ion anisotropies, exchange couplings and temperature on the magnetization, the susceptibility, the internal energy and the specific heat for the cylindrical core/shell nanowire system. In addition, we have also found the existence of two types of triple hysteresis loops behaviors for certain physical parameters. It is interesting to achieve satisfying results to compare our results obtained with other theoretical and experimental studies. Highlights • A cylindrical ferrimagnetic Ising nanowire with core/shell structure is proposed. • Effects of anisotropies and exchange couplings on the magnetic and thermodynamic properties of the system are discussed. • Phase diagrams in different parameters planes are obtained. • The triple hysteresis loops behavior is observed in the nanowire for certain physical parameters. [ABSTRACT FROM AUTHOR]

Entanglement of states is one of the most surprising and counterintuitive consequences of quantum mechanics, with potent applications in cryptography and computing. In organic semiconductor materials, one particularly significant manifestation is the spin-entangled triplet-pair state, which consists of a pair of localized triplet excitons coupled into an overall spin-0, -1, or -2 configuration. The most widely analyzed of these is the spin-0 pair, denoted 1(TT), which was initially invoked in the 1960s to explain delayed fluorescence in acene films. It is considered an essential gateway state for triplet-triplet annihilation and the reverse process, singlet fission, enabling interconversion between one singlet and two triplet excitons without any change in overall spin. This state has returned to the forefront of organic materials research in recent years, thanks both to its central role in the resurgent field of singlet fission and to its implication in a host of exotic new photophysical behaviors. Here we review the properties of triplet-pair states, from first principles to recent experimental results. [ABSTRACT FROM AUTHOR]

Magnetic properties of Tb/Cr/Ta film, for which the Curie temperature (TC) of ferromagnetic Tb is much lower than the Néel temperature (TN) of antiferromagnetic Cr, have been investigated. An apparent TC beyond that of pure Tb film was observed. The origin of this enhancement of TC is due to a magnetic proximity effect between Tb and Cr. In the temperature range of TC < T < TN, the coercivity HC and exchange bias field HE of the film show unusual temperature dependence. As the temperature increases from TC to TN, HE still exists and its sign changes from negative to positive with a low cooling field. At T > TN, HE turns to vanish. The coercivity HC exists not only at TC < T < TN, but also above TN. These unusual results can be discussed in terms of the pinned uncompensated spins and rotatable uncompensated spins in the interface. Additionally, the magnitude of the cooling field has a strong effect on HE, which probably results from the competition between the exchange coupling energy at the Tb/Cr interface and the Zeeman energy of the Cr surface magnetization. [ABSTRACT FROM AUTHOR]

The effects of La and Ce substitutions for Nd on the magnetic properties and intergranular exchange coupling of nanocrystalline (Nd 1-x M x ) y Fe 94-y B 6, (M = La and Ce; y = 10 and 12; x = 0–0.4) alloys have been investigated and presented in order to improve room temperature magnetic properties and reduce the rare earth content for NdFeB based alloys. Optimum magnetic properties such as remanent magnetization M r , maximum energy product ( BH ) max and coercivity H c up to 104 emu/g, 151 kJ/m 3 and 9.0 kOe have been obtained for as-quenched single phase (Nd 0.95 La 0.05 ) 12 Fe 82 B alloy. The decrease in M r for La/Ce substituted alloys is attributed to saturation magnetization reduction. An unusual increase in H c for 5% La substituted single phase alloy is speculated to the change in microstructure and magnetic phase separation. The analysis of remanence ratio, susceptibility curve, recoil loops and Henkel plots reveal that La substituted alloys exhibit strong ferromagnetic exchange coupling between hard magnetic phases or hard and soft phases than Ce substituted alloys due to the increase of exchange length and refine microstructure by La substitution. The present results indicate that partial substitution of Nd by La or Ce leads to various change behaviors for magnetic properties and inter-grain exchange coupling. [ABSTRACT FROM AUTHOR]

In materials with a good degree of magnetic interphase exchange coupling one has to consider both the extrinsic (microstructure) and intrinsic parameters (magnetisation, anisotropy, etc.) of the composite. This study investigates the feasibility of tuning the interphase exchange coupling condition by varying the anisotropy through the choice of the hard magnetic phase. The studied samples were produced by milling the hard magnetic phase along with 20 wt-% α-Fe powder for 6 h and subsequent annealing. The structure of the annealed powders was studied through X-ray diffraction and the magnetic properties of the nanocomposites were studied from demagnetisation curves and vs H plots in applied fields up to ±10 T. [ABSTRACT FROM AUTHOR]

Fe nanowire array with strong shape anisotropy was employed as the soft phase in Nd-Fe-B based nanocomposites. The effects of the Fe nanowire distribution on magnetic properties of the nanocomposites were investigated by micromagnetic simulation. The results indicate that the shape anisotropy of Fe wires added in the same direction as the uniaxial magnetocrystalline anisotropy of the hard phase cannot increase the coercivity of the nanocomposite. When the nanowires are distributed perpendicular to the easy axis of the hard phase, the shape anisotropy of soft phase can retard the moments from rotating to the full reversed direction, leading to enhanced coercivity. In addition, with increasing the nanowire diameter, the coercivity of the nanocomposite decreases, but the dipolar interaction shows different roles in magnetic reversal of nanocomposite for different distributions of nanowires. The current results suggest that the coercivity of the Nd2Fe14B/α-Fe nanocomposite can be enhanced by introducing the soft magnetic nanowire array with the diameter less than the exchange length and with the long axis along the direction other than the easy axis of hard phase. [ABSTRACT FROM AUTHOR]