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Artificial magnetic cilia are hair‐like structures that can respond to magnetic fields. Using hard magnetic materials in magnetic cilia makes possible programming and reprogramming of the magnetization state and corresponding actuation behaviors. Hard‐magnetic cilia are fabricated through self‐assembly by solvent casting of a slurry of NdFeB microparticles dispersed in a solution of a thermoplastic polyurethane elastomer. These hard‐magnetic cilia are capable of attractive and repulsive responses to magnetic fields, determined by the remanent magnetization of the NdFeB microparticles. An array of cilia can be magnetically reprogrammed through immobilization in ice, applying a damped alternating magnetic field first to reduce the remanent magnetization, and then remagnetizing the cilia with a large field. This demagnetization process significantly improves the reprogrammability of the cilia array. Different responses to magnetic fields can be programmed, including spatially nonuniform behaviors. Reprogrammed hard‐magnetic cilia exhibit unique behaviors in rotating magnetic fields. After reprogramming the magnetization direction along the width of the cilia, rotation and torsion cause them to slowly coil and then quickly uncoil in a snapping behavior. Modeling the magnetic and elastic torques during actuation provides additional insights and aids the design of magnetic cilia actuators based on hard magnets. [ABSTRACT FROM AUTHOR]

Geometry-induced domain wall pinning has been studied in heterostructure with soft magnet Fe3Pt and hard magnet FePt. It is demonstrated that the domain wall is pinned at the interface region of the Fe3Pt/FePt heterostructure under a small current field owing to the spin-transfer torque. The pinning of the domain wall is strongly dependent on the geometry of both soft and hard magnets. The thickness of the heterostructure Fe3Pt/FePt has an important influence on the pinning of the domain wall, which is caused by the combined effects of demagnetization, exchange coupling, and anisotropy. Moreover, with an increase in the width of the hard magnet FePt, the current of the pinning domain wall increases. With an increase in the width of the soft magnet, Fe3Pt, the pinning current decreased to a minimum value and then increased. These results are helpful for the fabrication and design of magnetic storage devices. [ABSTRACT FROM AUTHOR]

In this study, the temperature of the low-temperature reduction-diffusion (LTRD) process was successfully decreased to below 600 °C by introducing LiCl-KCl eutectic molten salt with a low eutectic point (352 °C) as a solvent for Ca reductant. Therefore, the Sm-Fe binary compounds, which were synthesizable at previously-unexplored low temperatures by the LTRD process using LiCl-KCl eutectic molten salt, were investigated, including whether a new metastable or ThMn12-type Sm-Fe binary phase was formed. The Sm-Fe phase transitions of the Sm-Fe binary compounds at a low temperature were identified, and it was found that MgCu2-type Sm-Fe, PuNi3-type Sm-Fe and TbCu7-type Sm-Fe phases were synthesized and stable at 400, 500 and 550 °C respectively. Although no new metastable Sm-Fe and ThMn12-type Sm-Fe compounds were discovered in this study, this work can demonstrate that it is possible to synthesize the Sm-Fe phase at very low temperatures by the LTRD process for the first time. [ABSTRACT FROM AUTHOR]

Most of large‐size permanent room‐temperature hard magnets contain rare‐earth elements. Here, we present the preparation of a large‐size rare‐earth free hard magnet based on the loading of the ordered mesoporosity of a preformed ordered mesoporous silica monolith obtained by a sol‐gel route with the Fe(NO3)3 salt, followed by a simple calcination in air. The investigation of the influence of the thermal treatment temperature as well as the Fe/Si ratio on the microstructure of the ϵ‐Fe2O3/SiO2 nanocomposites reveals well‐controlled ϵ‐Fe2O3 particles size and size distribution. Their magnetic study allows us i) to specify the size of the particles with an enhanced coercivity and ii) to show a linear correlation between the magnetic coercivity of the materials and the mass percent of these particles in the nanocomposites. A ϵ‐Fe2O3 based bulk hard magnet with the highest coercive field of 18 kOe at room temperature was obtained by this synthesis process. [ABSTRACT FROM AUTHOR]

Materials hosting noncollinear magnetic ordering and sizeable spin-orbit coupling can manifest perpendicular magnetic anisotropy and a Berry curvaturedriven intrinsic anomalous Hall effect. In this work, the structural, magnetic, and magnetotransport properties of crystalline hexagonal Heusler MnPtGa epitaxial thin films are reported. The centrosymmetric MnPtGa films (P63/mmc space group) crystallize with a preferred c-axis (0001) crystal orientation. Along this crystallographic direction, the MnPtGa films exhibit preferential perpendicular magnetic anisotropy, below the Curie temperature TC = 263 K, with a large effective uniaxial magnetic anisotropy Keff = 0.735 MJ m-3, at 150 K. In addition, the MnPtGa system undergoes a thermally induced spin reorientation transition below Tsr = 160 K, which marks the onset of a noncollinear spin-canted state. The anomalous Hall conductivity (AHC) of MnPtGa films exhibits a nonmonotonic behavior as a function of temperature, which changes sign at T* = 110 K. Concurrently with the reported unusual dependence of the AHC on the longitudinal conductivity in MnPtGa crystalline thin films, these findings strongly suggest an anomalous Hall effect of intrinsic origin, driven by a momentum-space Berry curvature mechanism, as supported by first-principle calculations. [ABSTRACT FROM AUTHOR]

Abstract Materials hosting noncollinear magnetic ordering and sizeable spin‐orbit coupling can manifest perpendicular magnetic anisotropy and a Berry curvature‐driven intrinsic anomalous Hall effect. In this work, the structural, magnetic, and magnetotransport properties of crystalline hexagonal Heusler MnPtGa epitaxial thin films are reported. The centrosymmetric MnPtGa films (P63/mmc space group) crystallize with a preferred c‐axis (0001) crystal orientation. Along this crystallographic direction, the MnPtGa films exhibit preferential perpendicular magnetic anisotropy, below the Curie temperature TC = 263 K, with a large effective uniaxial magnetic anisotropy Keff = 0.735 MJ m−3, at 150 K. In addition, the MnPtGa system undergoes a thermally induced spin reorientation transition below Tsr = 160 K, which marks the onset of a noncollinear spin‐canted state. The anomalous Hall conductivity (AHC) of MnPtGa films exhibits a nonmonotonic behavior as a function of temperature, which changes sign at T* = 110 K. Concurrently with the reported unusual dependence of the AHC on the longitudinal conductivity in MnPtGa crystalline thin films, these findings strongly suggest an anomalous Hall effect of intrinsic origin, driven by a momentum‐space Berry curvature mechanism, as supported by first‐principle calculations.

Rare-earth-free MnAl-C-Ni permanent magnets have been produced for the first time by extruding powders milled from bulk. The resulting materials, fabricated using different conditions, contained a large volume fraction (> 0.92) of the desired τ-phase. In terms of the maximum energy product, the best performance obtained for a whole, transverse section of the extruded material was (BH) max = 46 kJm−3, and was (BH) max = 49 kJm−3 for a sample taken from near the edge of this section. Analysis showed that this material was comparable to the long-established benchmark, comprising MnAl-C-based magnets extruded in industry from bulk or from gas-atomised powder. Such materials are no longer available. The microstructure of the materials produced here consisted of fine, recrystallised grains, which exhibited an <001> fibre texture with intermediate texture quality and of larger, non-recrystallised regions, which contained hierarchical twinning and a high density of defects. The volume fraction and size of the non-recrystallised regions was greatly reduced by decreasing the size of the initial powder particles. This led to a large increase in the squareness factor of the demagnetisation curve and consequently to the high (BH) max values observed. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We studied the phase stability of Ce-substituted magnetoplumbite-type Sr ferrite under various oxygen pressures. We have successfully obtained Ce-substituted samples as revealed from X-ray diffraction and wavelength dispersion X-ray analyses. The solubility limit of Ce in Sr1-xCexFe12O19 was estimated to be $x = 0.24$ at ambient pressure, which is reduced to 0.05–0.10 under higher oxygen pressures. The variation of the $c$ -axis against $x$ and the reduction of the solubility by increasing oxygen pressure suggests that the valence of Ce is not 4+ but 3+. The solubility limit of Ce is dominated not only by the ionic radius but also by the valence instability of Ce. [ABSTRACT FROM AUTHOR]

The magnetomechanical actuation of micropillars is developed for the contactless manipulation of miniaturized actuators and microtextured surfaces. Anisotropic geometry of micropillars can significantly enhance the magnetic actuation compared with their isotropic counterparts by directional stress distributions. However, this strategy is not viable for triangular micropillars owing to insufficient anisotropy. In this study, a significant improvement in the magnetic actuation of triangular micropillars using composite magnetic particles is reported. A minute and optimal amount of hard magnetic gamma-ferrite nanorods are hybridized with soft magnetic iron microspheres to generate synergistic effects of magnetic coupling and percolation phenomenon on the magnetic actuation of polymer composites. The addition of 1 wt% face-centered cubic-phased gamma-ferrite nanorods suppresses the magnetic coupling interference of body-centered cubic-phased iron microspheres. Furthermore, the nanorods reduce the percolation threshold by participating in the percolation of the microspheres. A systematic compositional study on the magnetization and magnetorheological properties reveals that the coupling effect dominates the percolation effect at a low magnetic field, whereas the percolation effect governs the magnetic actuation at a high magnetic field. This hybrid approach can help in designing material constituents for effective magnetic actuators and robotic systems that can sensitively respond to an external magnetic field., (© 2023 Wiley-VCH GmbH.)

Abstract The rare-earth-free hard magnetic L1 0 -FeNi phase found in cosmic meteorites demonstrates potential as a next-generation permanent magnet. However, it is very difficult to artificially produce the L1 0 -FeNi phase due to the low atomic diffusion coefficients of Fe and Ni near the order-disorder transition temperature (∼320 °C). Therefore, FeNiPC amorphous alloy systems exhibiting crystallization temperature (T x) near the transition temperature were investigated. The amorphous alloys were annealed at T x , resulting in high atomic diffusion. The structural and microstructural characterizations of annealed ribbons revealed the formation of L1 0 -FeNi phase through observation of the superlattice peak. The magnetic property, such as coercivity (H c), also indicated the formation of L1 0 -FeNi phase, because the maximum H c value is 641 Oe after the annealing process. [ABSTRACT FROM AUTHOR]

The work outlined in this paper demonstrates significant improvements in ductility during the Hydrogen Ductilisation Process (HyDP) [1] of a Neomax-type alloy and, for the first time, complete ductility of a sub-stoichiometric alloy. In previous studies, the uniformity of the ductilisation transformation was limited by the presence of the NdFe 4 B 4 phase not undergoing complete disproportionation, which left extremely brittle, micron-scale islands in a highly ductile disproportionated matrix. The present works investigated the influence of a significantly longer (18 h) hydrogen treatment of the Neomax-type alloy to observe whether the completely disproportionated NdFe 4 B 4 phase is as ductile as the disproportionated matrix. It has been observed that, when the NdFe 4 B 4 phase is completely disproportionated, it exhibits similar ductility to that of the disproportionated matrix, showing no sign of cracking under a compressive load. However, inhomogeneity in the book mould material leads to varying quantities of NdFe 4 B 4 phase and thus, varying levels of disproportionation. Despite this, significant improvements were observed in the mechanical behaviour of the Neomax-type alloy. The longer disproportionation treatment also results in larger grains and thus, a lower final coercivity in the recombined state than that of the previous 5 h treatment. For comparison, the mechanical behaviour of a sub-stoichiometric alloy, which did not contain any NdFe 4 B 4 phase, has also been studied. The compression behaviour of this sub-stoichiometric alloy in the disproportionated state was found to be completely ductile. It is clear from this work that it is possible to create a completely ductile NdFeB material directly from the solid cast alloy which, in the future, could have significant implications for NdFeB magnet production. [ABSTRACT FROM AUTHOR]

An experiment was carried out to investigate the influence of CaCO 3 and SiO 2 additives on the magnetic and physical properties of M-type Sr ferrites by changing experimental parameters such as the additive composition and Ca/Si ratio. Specimens were prepared by conventional ceramic techniques. It was found that the magnetic properties (B r  = 4.42 kG, iH c  = 3.32 kOe and (BH) max  = 4.863 MGOe) were considerably improved upon adding CaCO 3  = 1.1% and SiO 2  = 0.4 wt% together with Co 3 O 4 , and the mechanical properties thereof were acceptable for motor applications. It was revealed that CaCO 3 and SiO 2 additives led to an upswing in the magnetic properties via the enhancement of uniform grain growth, particle alignment, and the densification of Sr ferrite. [ABSTRACT FROM AUTHOR]

An experiment was performed to investigate whether CaCO 3 and SiO 2 addition enhances the magnetic properties of cobalt-free M-type Sr ferrites, in which experimental parameters such as additive composition and the CaCO 3 /SiO 2 ratio were changed. The specimens were prepared using conventional ceramic techniques. CaCO 3 addition promoted densification and uniform grain growth, resulting in high remanence; however, with the simultaneous addition of CaCO 3 and SiO 2 , coercivity decreased to 3046 Oe in Sr ferrite hard magnets without Co 3 O 4 . SiO 2 addition suppressed grain growth. The addition of appropriate concentrations of CaCO 3 and SiO 2 as additives after calcination was shown to be very beneficial for tailoring a dense microstructure with relatively small grains. A CaCO 3 /SiO 2 ratio of approximately 1.8 was found to be optimum, and the magnetic properties of B r = 4.3 kG, i H c = 3.7 kOe, and ( BH ) max = 4.5 MGOe were obtained for Sr ferrite hard magnets without Co 3 O 4 , which are acceptable for motor applications under output power <1 kW. [ABSTRACT FROM AUTHOR]

We have grown Sm(Fe 1 − x Co x ) 12 ( x = 0, 0.1 and 0.2) films epitaxially on V(001) buffered MgO(001) single crystalline substrates in order to investigate the intrinsic hard magnetic properties of the Co substituted SmFe 12 phase with the ThMn 12 structure. We found Sm(Fe 0.8 Co 0.2 ) 12 has excellent intrinsic hard magnetic properties with spontaneous magnetization of 1.78 T, anisotropy field of 12 T and Curie temperature of 859 K, all of which are superior to those for Nd 2 Fe 14 B. Hence, the Sm(Fe 0.8 Co 0.2 ) 12 compound is promising as permanent magnet material, if it can be stabilized in a bulk form. [ABSTRACT FROM AUTHOR]

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In current work, Nd2Fe14B nanoparticles was synthesized by sol-gel method. Dysprosium powders were added into Nd2Fe14B nanoparticles by mechanical alloying process in order to enhancement of coercivity. The phase analysis, structure, and magnetic properties of annealed (Nd 1−x Dy x ) 2 Fe 14 B nanoparticles with different Dy-content (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were investigated by employing X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, field emission scanning electron microscope, transmission electron microscope and vibrating sample magnetometer techniques. The results showed that with an increase in Dy amounts, the coercivity of particles increased from 2.9 kOe to 13.4 kOe and then decreased to 5.6 kOe. By adding an optimum amount of Dy (x=0.4), the coercivity was significantly increased from 2.9 kOe to 13.4 kOe. The average particle size of annealed (Nd 1−x Dy x ) 2 Fe 14 B nanoparticles was below 10 nm. Magnetization reversal studies indicate that the coercivity of milled and annealed (Nd 1−x Dy x ) 2 Fe 14 B nanoparticles is controlled by the nucleation of reversed magnetic domains. The experimental results in the angular dependence of coercivity for (Nd 1−x Dy x ) 2 Fe 14 B permanent magnets showed that the normalized coercivity of the permanent magnets H c (θ)/H c (0) increases from 1 to about 1.2–1.5 with increasing θ from 0 to about π/3, for x=0.4–0.6. [ABSTRACT FROM AUTHOR]

Hard magnetic SrFeAlO hexaferrite and soft magnetic FeO ferrite with cubic spinel structure were synthesized by Pechini method and subsequently mixed and sinterized to obtain an isotropic, polycrystalline SrFeAlO/FeO nanocomposite. A noticeable coercivity of 648 kA/m was observed, together with a saturation magnetization of 0.2 T. The magnetization reversal process for the nanocomposite was described in terms of recoil area and Henkel plots. Field intensity range between 0 and 600 kA/m was identified as a favoring magnetizing interaction, whereas at higher fields, dipolar interactions destabilize magnetized states favoring magnetization reversal. The field interval for which the intergranular exchange interaction facilitates reversible coherent rotation between constituent grains was determined within 0-220 kA/m. Above 220 kA/m, a progressive deterioration of the exchange coupling gives way to the demagnetizing process towards full magnetization reversal. [ABSTRACT FROM AUTHOR]

High coercivity Sm 2 Fe 17 N 3 submicron size powder was synthesized by the polymerized-complex (PC), hydrogen reduction (HR) and reduction–diffusion (RD) processes. A mixture of nano size SmO x , FeO x and SmFeO 3 particles was first synthesized by the polymerized-complex method, which was then reduced to α-Fe and SmO x by hydrogen. Subsequent reduction diffusion using Ca metal led to the formation of submicron size Sm 2 Fe 17 powder with a mixture of CaO. After nitriding and rinsing, Sm 2 Fe 17 N 3 powder with the average diameter of 0.69 ± 0.17 μm was obtained, which exhibited the coercivity of 2.32 T, the highest ever reported for ternary Sm 2 Fe 17 N 3 anisotropic powder. [ABSTRACT FROM AUTHOR]

In the current work , BaZn x Zr x Fe 12-2x O 19 (x ​= ​0.00–0.15) sub-micron particles synthesis with the help of the sol-gel auto-combustion technique has been carried out. XRD studies reveal the single BaM (barium hexaferrite of M-type) phase formation and undesirable phases such as BaFe 2 O 4 and α–Fe 2 O 3 absent. The FE-SEM micrographs suggest that the size of grain increases from ≈241 ​nm (x ​= ​0.00) to ​≈ ​280 ​nm (x ​= ​0.15) with a substitution level. The enhancement in grain size with composition has been also confirmed by the dynamic light scattering technique (DLS). The coercivity (H c) has been continuously decrease from 5363 ​Oe (x ​= ​0.00) to 4211 ​Oe (x ​= ​0.15) with increase in non-magnetic dopant concentration. On the other hand, the saturation magnetization (M s) value increases from 70.87 emu/g (x ​= ​0.00) to 87.04 emu/g (x ​= ​0.15) with substitution. In the sol-gel auto-combustion synthesis of M-type hexaferrite, fuel plays an important role. It affects the magnetic properties, surface morphology, and calcination temperature of hexaferrite. In the present study, synthesis of Zr4+-Zn2+ doped BaM having a low composition (x ​= ​0.00–0.15) using tartaric acid as fuel is first reported. The enhanced magnetic properties of Zr4+-Zn2+ doped BaM samples over undoped samples can be used in permanent magnet appliances. [Display omitted] • XRD data indicates all the samples were phase pure. • Raman peak broadening indicates local straining in crystal lattice with substitution. • Grain size monotonically increases with Zn2+/Zr4+ substitution. • Maximum value of M s is 87.04 emu/g in x ​= ​0.15 sample. • H c continuously decreases from 5363 to 4160 ​Oe with Zn2+/Zr4+ substitution. [ABSTRACT FROM AUTHOR]

The hollow BaFe12O19 submicron spheres (HBSSs) for advanced functional magnetic materials were synthesized successfully by self assembly method using diethyleneamine (DEA). The optimized concentration of DEA surfactant was found to be 1.1 mL with pH > 12.2 for the elaborate hollow sphere structure. The coercivity and remanence properties of HBSSs with 500-nm-sized showed 4.2 kOe (iHc) and 2.2 kG (Br), respectively. These results revealed that HBSSs particles were successfully synthesized to submicron size with the quantitative compounding of barium and ferrite precursors. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the texturing of bulk α-Fe/Nd2Fe14B nanocomposites produced from Nd-lean amorphous Nd x Fe92.5−x Cu1.5B6 (x=9 to 11.5at%) via a hot deformation under a uniaxial stress of ~350MPa at 973K has been studied. An enhanced (00l) texture of the hard phase is observed with increasing Nd content, which results in an increase in the magnetic anisotropy of the nanocomposite magnets. As a result, both the coercivity and the remanence of the magnets increase simultaneously with increasing Nd content from x=9–11.5at%, yielding a significant enhancement of the maximum energy product from (BH)max=13.2 to 17.5MGOe in the direction parallel to stress axis. [Copyright &y& Elsevier]

Residual stress in electroplated hard magnetic layers is crucial to the stability and durability in end applications. We electrodeposited highly HCP (002) textured CoMnP hard magnetic layers on copper substrate. We characterized and compared the residual stresses of mono- and multi-layered configurations using sin2ψ X-ray diffraction (XRD) for the apparent crystallite stress (σ XRD), and curvature measurement methods for the macro-stress (σ f). Intermediate Cu layer having a fixed thickness of 1.4 μm was introduced as a stress reliever for the multilayered CoMnP/Cu through sequential electrodeposition. In multilayers, thickness of all single magnetic layers was added to around ~20 μm similar to that of a monolayer. The surface morphology, layer composition and microstructure remain the same regardless of individual CoMnP single layer thickness. XRD results of ϕ-scan and ψ-scan depict the transversely isotropic CoMnP layers are under an equi-biaxial stress status, making a simplified analytical solution of sin2ψ method. The residual stresses measured by XRD sin2ψ method have been correlated with those acquired by curvature method. Increasing the number of layers from 2, 3 to 6 in the CoMnP/Cu multilayers reduces the σ XRD by 8.3%, 25%, 33%, respectively; while the σ f by 7.7%, 15% and 23%, respectively, as compared to those of the CoMnP mono-layer. These reductions are attributed to the released strain energy due to soft interlayer confinement and stacking fault formation. Elaborated includes unambiguous understandings of residual stress and microstructures for the electrodeposited CoMnP layers. • CoMnP/Cu hard magnetic multilayers have been electrodeposited on copper substrate. • Insertion of the Cu interlayer reduces the curvature for the CoMnP layers. • The residual stresses measured by XRD sin2ψ and curvature methods are correlated. • The relief of residual stress is attributed to the released strain energy. • The electrodeposited CoMnP/Cu multilayers can be tuned for material properties. [ABSTRACT FROM AUTHOR]

• A rare earth free MnAl-C-Ni magnet with (BH) max = 43 kJ m−3 was obtained through extruding pulverised melt-spun ribbons. • The extrusion of pulverised melt-spun ribbons offers a way to eliminate the existence of the non-recrystallised regions. • The absence of the non-recrystallised regions is attributed to the hindrance of deformation twinning due to the small size of initial τ-grains. [Display omitted] MnAl-C-Ni magnets with maximum energy products, (BH) max ≥ 42 kJ m−3, were produced by hot extruding pulverised melt-spun ribbons. The small diameter of the columnar grains in the as-spun ribbons (1 µm ≤ d ≤ 6 µm), restricted the maximum size of the τ-phase grains, which formed during the holding process at 700 °C before the extrusion. The absence of non-recrystallised regions in the extruded material made from ribbons produced at high wheel speed was attributed to this smaller initial τ-phase grain size (1 µm ≤ d ≤ 2 µm) and resulted in an enhancement of the squareness factor of the demagnetisation curve. [ABSTRACT FROM AUTHOR]

Abstract: The base alloys of nominal composition (Nd0.75Pr0.25) y FebalanceB x (y=10−9.2 and x=6−19.2) were chosen to study the influence of RE/B ratio, smaller than stochiometric composition on magnetic properties of over quenched and annealed ribbons. From X-ray diffraction analysis of these ribbons, the α-Fe and Fe3B phases were observed along with (Nd,Pr)2Fe14B major phase. The average grain size was calculated using these patterns as: 35nm for α-Fe, 45nm for (Nd,Pr)2Fe14B and 22nm for Fe3B particles. TEM analysis also supported the nano distribution of the above phases. These X-ray graphs support the idea of exchange coupling between hard and soft phases responsible for the observed magnetic properties. In these ribbons the saturation magnetization J s and remnant magnetization J r increases from 1.19T to 1.66T and from 0.65T to 0.91T, respectively as RE/B ratio increases. The increase in J s and J r may be attributed to the presence of exchange coupling between these phases. The corresponding coercivity j H c decreases from 673.33 to 271.33kAm−1. The maximum energy product (BH)max initially increases from 72.42kJm−3to 109.85kJm−3 up to RE/B≈1 and then decreases to 58.5kJm−3, depending on the shape of second quadrant B–H loop. The coercivity mechanism observed from initial hysteresis curve was considered to be nucleation of domain wall. [Copyright &y& Elsevier]

We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180 °C. Crystalline phase of samples were determined by XRD and spectroscopic, morphological, and magnetic investigation of the sample were FT-IR, SEM, and TG analysis, respectively. XRD analysis revealed few impurity phases in the as-made powder; upon calcinations, the material is converted to desired hexaferrite phase. As synthesized powder exhibits agglomerates with rather smooth facets, in the form of thick platelets. Upon calcination, all these structures were observed to transfer to rod-like structures. The As calcined sample has high specific saturation magnetization ( M) values of 65 emu/g that is close to its theoretical value of 74.3 emu/g but the hydrothermally synthesized sample does not. This is in agreement with the observations from XRD analysis where few impurity phases observed in the as-made powder cause a weak magnetic response. Upon calcination, the material is converted to a desired hexaferrite phase with better magnetic properties. [ABSTRACT FROM AUTHOR]

KFe(OH)(SO)(HO) was prepared by hydrothermal synthesis. The crystal structure is the isomorphous phase of KCo(OH)(SO)(HO). Mössbauer spectra of KFe(OH)(SO)(HO) were measured at low temperatures between room temperature and 14 K, and the hyperfine interactions were analyzed. The Neel temperature is 39 K. Two paramagnetic Fe species were observed in the Mössbauer spectrum at room temperature, and Mössbauer spectra measured below 38 K were decomposed into four magnetic subspectra. From the temperature dependence, it is found that the local electron density at each site is largely deviating at low temperatures, which may induce the giant coercivity. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a process that develops texture in nanocrystalline permanent magnet alloys is presented. An originally isotropic material is passed through a high up-temperature gradient, inducing directional grain growth. Texture development by directional annealing of melt-spun Sm12Co88, (Sm12Co88)99Nb1, (Sm12Co88)99C1, and (Sm12Co88)98Nb1C1 alloys was examined. Samples directionally annealed were compared with conventionally annealed samples. Strong (006) in-plane texture was observed by X-ray diffraction in Sm12Co88 and (Sm12Co88)99Nb1 alloys and the anisotropy was corroborated by magnetic measurements (magnetic texture ∼20–53%). Directional annealing produced only slight texture in the (Sm12Co88)99C1 and (Sm12Co88)98Nb1C1 alloys. The development of texture is critically dependent on annealing temperature, the up-temperature gradient, translational velocity, and alloy composition. The activation energy for anisotropic grain growth was estimated to be ∼28 and ∼42kJmol−1 for Sm12Co88 and (Sm12Co88)99Nb1, respectively. These results indicate that directional annealing as a route to texture development in nanocrystalline permanent magnet alloys is a feasible process. [Copyright &y& Elsevier]

Abstract: Single-phase M-type hexagonal ferrites Sr1− x La x Fe12O19 (0≤x≤1) were prepared by a ceramic route. The stability limits of the ferrite phases were determined with a combination of various microscopy techniques, electron-probe micro-analysis, powder X-ray diffraction and thermal analysis. SrFe12O19 (x=0) is stable up to 1420°C, whereas LaFe12O19 (x=1) exists between 1360 and 1400°C only. The lattice parameters of Sr1− x La x Fe12O19 exhibit a linear variation with x, i.e. a 0 slightly increases and c 0 decreases with x, leading to a decrease of the unit cell volume with x. The saturation magnetization at T=5K decreases with increasing La concentration. Room temperature Mössbauer analysis shows that the Fe3+/Fe2+ valence change occurs in the 2a sites for the whole composition range. [Copyright &y& Elsevier]

Abstract: Nanocrystalline strontium hexaferrite (SrFe12O19) powders have been synthesized using the co-precipitation–calcination route. The ferrite precursors were obtained from aqueous mixtures of strontium carbonate and ferric chloride by precipitating strontium and iron ions using 5M sodium hydroxide solution. These precursors were calcined at different temperatures ranging from 800 to 1100°C for constant calcination time 2h in a static air atmosphere. Effects of Fe3+/Sr2+ mole ratio, annealing temperature and pH on the formation, crystalline size, morphology and magnetic properties were systematically studied. The powders formed were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and VSM. The results obtained showed that the single-phase SrFe12O19 powders were achieved by decreasing the Fe3+/Sr2+ mole ratio from the stoichiometric value 12 to 9.23 and increasing the annealing temperature up to 900°C for 2h and pH 10. The maximum saturation magnetization (84.15emu/g) was achieved by decreasing the Fe3+/Sr2+ mole ratio to 9.23 and the annealing temperature 1000°C, annealing time 2h and pH 10 due to the formation of a plate-like hexagonal-shape structure. Wide coercivities (2937–5607Oe) can be obtained at different synthesis conditions. Moreover, the microstructure and the magnetic properties of the produced Sr–M ferrite powders were strongly dependent on he synthesis conditions. [Copyright &y& Elsevier]

Abstract: The effect of non-contact electric fields applied directly during combustion synthesis of barium ferrites is presented. The microstructure, phase composition and magnetic characteristics of the combustion products were obtained by scanning electronic microscopy (SEM), X-ray diffraction and vibrating sample magnetometry (VSM). A correlation was found between the observed magnetic properties of the product and the magnitude of the applied electric field. The role of oxygen exchange activated by the electric field during the combustion synthesis is discussed. [Copyright &y& Elsevier]

Abstract: A new dual-phase nanocomposite magnet, made up of the well-coupled Sm3(Fe,Ti)29N x and α-Fe nano-crystals, has been successfully fabricated by the melt-spun technique. Measurements of magnetic properties reveal that the hysteresis loop shows up the notable characteristics of single hard magnet in the well-crystallized samples. The electron microscopy investigations indicate that the grain sizes in our samples in general range from 30 to 60nm for Sm3(Fe,Ti)29N x and from 10 to 20nm for α-Fe, grain boundaries between the Sm3(Fe,Ti)29N x and α-Fe phases are clean without any impurities. These structural features are fundamentally compatible with direct exchange-coupling between these two magnetic phases. [Copyright &y& Elsevier]

Monodispersed α-Fe nanoparticles were synthesized under an argon atmosphere via thermal decomposition of Fe2+-oleate2. Nd–Fe–B ultrafine amorphous alloy particles were prepared by reaction of metal ions with borohydride in aqueous solution. Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets have been prepared by self-assembly using surfactant. The crystal structure of the synthesized nanoparticles was identified by using X-ray powder diffraction (XRD). The size and shape of nanoparticles were obtained by TEM. Thermogravimetry using a microbalance with magnetic field gradient positioned below the sample was used for the measurement of a thermomagnetic analysis (TMA) curve showing the downward magnetic force versus temperature. [ABSTRACT FROM AUTHOR]

Abstract: Bi-directional polyimide (PI) electromagnetic microactuator with different geometries are designed, fabricated and tested. Fabrication of the electromagnetic microactuator consists of 10μm thick Ni/Fe (80/20) permalloy deposition on the PI diaphragm by electroplating, high aspect ratio electroplating of copper planar coil with 10μm in thickness, bulk micromachining, and excimer laser selective ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems during wafer etching. A mathematical model is created by ANSYS software to analyze the microactuator. The external magnetic field intensity (Hext) generated by the planar coil is simulated by ANSYS software. ANSYS software is used to predict the deflection angle of the microactuator. Besides, to provide bi-directional and large deflection angle of microactuator, hard magnet Fe/Pt is deposited at a low temperature of 300°C by sputtering onto the PI diaphragm to produce a perpendicular magnetic anisotropic field. This magnetic field can enhance the interaction with Hext to induce attractive and repulsive bi-directional force to provide large displacement. The results of magnetic microactuator with and without hard magnets are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one. [Copyright &y& Elsevier]

A systematic study of syntheses, crystallographic and magnetic properties of the Ho3Fe27.0V2.0 and Ho3Fe29-xCrx (x=3.0 and 3.5) compounds has been performed in this work. The lattice parameters, Curie temperature TC, the saturation magnetization MS and the anisotropy field HA—at 4.2 K and room temperature—for the Ho3Fe29-xTx (T=V and Cr) compounds were obtained. Spin reorientations of easy magnetization direction (EMD) are observed at around 150 K for Ho3Fe27.0V2.0 and Ho3Fe29-xCrx (x=3.0 and 3.5). First order magnetization process (FOMP) occurs in magnetization curves at 1.5 K for the magnetically aligned samples of Ho3Fe27.0V2.0 and Ho3Fe25.5Cr3.5. [Copyright &y& Elsevier]

A novel polyimide-based magnetic microactuator is presented. Two types of magnetic microactuators with different beams in dimension are fabricated, tested and demonstrated. The combination process of thick photoresist lithography, micro-electroplating, bulk micromachining, and excimer laser ablation is performed. Polyimide diaphragm with micro-electroplated Ni/Fe (80/20) permalloy is bulk micromachined firstly, and then polyimide microstructures are ablated by mask projection of 248 nm excimer laser. This new concept demonstrates that polyimide microstructures can be post-ablated after bulk micromachining. To provide large deflection angle of microactuators, hard magnetic Fe/Pt is deposited under low temperature less than 300 °C by sputtering onto the polyimide suspension diaphragm to produce a perpendicular magnetic anisotropic field. This anisotropic field can enhance the interaction with the external magnetic field intensity (Hext) to induce attractive and repulsive force to provide large displacement. The results of magnetic microactuators with and without hard magnetic are compared and discussed. The preliminary result reveals that the electromagnetic microactuator with hard magnet shows a greater deflection angle than that without one. Besides, ANSYS software was used to simulate the deflection angle of the microactuators. The experimental result shows a good agreement with theoretical simulation. [Copyright &y& Elsevier]

The effects of Zr and C additions on the magnetic properties and microstructures of melt-spun Fe83-xZrxNd10B7-yCy (x=0–5, y=0–7) alloys were investigated. The cooling rates of melts were varied by changing the wheel surface velocity to optimize hard magnetic properties. The Zr addition decreased the size of the crystalline grains and increased the coercivity from 6.6 kOe for Fe83Nd10B6C1 to 10.7 kOe for Fe78Zr5Nd10B6C1. The C addition compensates the decrease of remanence caused by the addition of Zr. The (BH)max of 145 kJ/m3 was obtained from an optimally cooled Fe80Zr3Nd10B6C1 alloy. [Copyright &y& Elsevier]

This paper presents the results of a parametric investigation of the strength and fracture toughness of Sm2Co17 type permanent magnets in the Sm(Co,Fe,Cu,Zr)7−8 family of alloys. The strength and fracture toughness of the as-received materials were characterized as a function of temperature, loading direction, and magnetization. Since these magnets are candidates for applications with service temperatures up to 450°C, the effect of thermal exposure on the mechanical properties was determined by characterizing the properties after a thermal treatment of 40 h at 450°C. [Copyright &y& Elsevier]

The effect of minor elements (Cu, Nb, Zr and/or Ga) on the microstructure and magnetic properties of α-Fe/Nd2Fe14B nanocomposites obtained by melt-spinning Nd8Fe87B5 based alloys has been studied by using three-dimensional atom probe and transmission electron microscopy. Cu atoms form clusters prior to the crystallization of amorphous precursors. However, Cu clusters do not act as heterogeneous nucleation sites for the α-Fe crystals; thus, Cu addition is not beneficial for reducing the grain size of α-Fe/Nd2Fe14B nanocomposites. On the other hand, Nb is effective in suppressing grain growth while annealing an partially crystallized melt-spun Nb-containing alloy. However, it was not possible to optimize the microstructures and magnetic properties by crystallizing Nb-containing amorphous precursors. The hard magnetic properties with Hc=496 kA/m and (BH)max=134 kJ/m3 were obtained by adding a small amount of Zr. The coercivity was enhanced by combined addition of Zr and Ga. Zr and Ga atoms are partitioned into the Nd2Fe14B phase, and evidence for a slight enrichment of Zr atoms at the α-Fe/Nd2Fe14B interfaces has been found. [Copyright &y& Elsevier]

The NdFe 12 N x compound with a ThMn 12 structure (space group I 4/ mmm ) was successfully synthesized by nitriding an NdFe 12 layer grown on a W underlayer on a single-crystalline MgO(001) substrate. The c -axis expanded from 0.480 to 0.492 nm while the a -axis showed a slight contraction from 0.852 to 0.849 nm after the nitriding. Excellent intrinsic hard magnetic properties of μ 0 M s ≈ 1.66 ± 0.08 T, μ 0 H a ≈ 8 T, and T c ≈ 550 °C, which are superior to those of Nd 2 Fe 14 B, were obtained. [ABSTRACT FROM AUTHOR]