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Efficient and cost-effective soft magnetic materials (SMMs) are essential for accelerating the adoption of electric vehicles and the sustainable growth of renewable electricity. While amorphous and nanocrystalline SMMs offer remarkably low magnetic losses, their poor mechanical properties, limited availability in size and shape (particularly ribbon widths), and high cost prevent them from widespread industrial application. Here, we show that ductile Fe-6.5%Si 2-D flakes could be used as building blocks for making high performance bulk SMMs. This approach bypasses the brittleness problem and creates a new morphology and a new fabrication method for the SMMs with improved energy efficiency and lower processing cost. Ductile Fe-6.5%Si flakes are mass-produced by melt spinning and are then consolidated to bulk SMMs with a brick-wall type of structure. The novel process introduces anisotropic electrical and magnetic properties and enables near net shape processing. Resulting Fe-6.5%Si thin sheets display low iron loss (W10/400 = 6.1 W/kg) and high permeability (µr = 28,000), which are comparable to the current state of the art high silicon steel. CaF2 coating reduces the iron losses for thick Fe-6.5%Si parts. Polymer coated Fe-6.5%Si flake cores show potential for high power inductors with greater permeability and lower losses than traditional powder cores.

MnBi is an attractive rare-earth-free permanent magnetic material due to its low materials cost, high magnetocrystalline anisotropy (1.6 × 106 J m−3), and good magnetization (81 emu g−1) at room temperature. Although the theoretical maximum energy product (BH)max of 20 MGOe is lower than that of NdFeB-based magnets, the low temperature phase (LTP) of MnBi has a positive temperature coefficient of coercivity, up to 200 °C, which makes it a potential candidate for high temperature applications such as permanent magnet motors. However, the oxygen sensitivity of the MnBi compound and the peritectic reaction between Mn and Bi make it difficult to synthesize into a material with high purity. This challenge is partly offset by adding excess Mn to the alloy, with composition close to Mn55Bi45 resulting in the highest saturation magnetization after common processing techniques such as arc melting, casting, melt spinning, and ball milling. Here we report a systematic process which reduces the amount of excessive Mn, while simultaneously providing a large saturation magnetization (MS) of 79 emu g−1 at 300 K in the annealed Mn52Bi48 ribbons. We also report excellent magnetic properties in the ball powders, resulting in 0.5–5 µm particles with MS of 75.5 emu g−1, coercivity Hci of 10.8 kOe, and (BH)max of 13 MGOe using 9 T applied field at 300 K. A secondary annealing treatment on various ball milled powders increased Hci by up to 21%, and also resulted in an increase in MS up to 78.8 emu g−1.

In the processing of commercial rare earth permanent magnets, use of external magnetic fields is limited mainly to the alignment of anisotropic particles and the polarization of the finished magnets. Here we explore the effects of high magnetic fields on earlier stages of magnet synthesis, including the crystallization and chemical phase transformations that produce the 2:14:1 phase in the Pr-Co-B system. Pr 2 Co 14 B alloys produced by melt-spinning were annealed in the presence of strong applied magnetic fields (H=90 kOe). The resulting materials were characterized by x-ray diffraction, electron microscopy, and magnetization measurements. We find that magnetic fields suppress the nucleation and growth of crystalline phases, resulting in significantly smaller particle sizes. In addition, magnetic fields applied during processing strongly affects chemical phase selection, suppressing the formation of Pr 2 Co 14 B and α -Co in favor of Pr 2 Co 17 . The results demonstrate that increased control over key microstructural properties is achievable by including a strong magnetic field as a processing parameter for rare-earth magnet materials.

Neutron diffraction and magnetic susceptibility studies of orthorhombic single crystal $({\mathrm{Sr}}_{0.97}{\mathrm{K}}_{0.03}){\mathrm{MnSb}}_{2}$ confirm the three-dimensional (3D) C-type antiferromagnetic (AFM) ordering of the ${\mathrm{Mn}}^{2+}$ moments at ${T}_{\mathrm{N}}=305\ifmmode\pm\else\textpm\fi{}3$ K, which is slightly higher than that of the parent ${\mathrm{SrMnSb}}_{2}$ with ${T}_{\mathrm{N}}=297\ifmmode\pm\else\textpm\fi{}3$ K. Susceptibility measurements of the K-doped and parent crystals above ${T}_{\mathrm{N}}$ are characteristic of 2D AFM systems. This is consistent with high-temperature neutron diffraction of the parent compound that displays persisting 2D AFM correlations well above ${T}_{\mathrm{N}}$ to at least $\ensuremath{\sim}560$ K with no evidence of a ferromagnetic phase. Analysis of the de Haas--van Alphen magnetic oscillations of the K-doped crystal is consistent with hole doping.

Employing elastic and inelastic neutron scattering (INS) techniques, we report on the microscopic properties of the ferromagnetism in the dilute magnetic topological insulator ${({\mathrm{Bi}}_{0.95}{\mathrm{Mn}}_{0.05})}_{2}{\mathrm{Te}}_{3}$. Neutron diffraction of polycrystalline samples shows the ferromagnetic (FM) ordering is long range within the basal plane, and mainly two dimensional (2D) in character with short-range correlations between layers below ${T}_{\mathrm{C}}\ensuremath{\approx}13$ K. Remarkably, we observe gapped and collective magnetic excitations in this dilute magnetic system. The excitations appear typical of quasi-2D FM systems despite the severe broadening of short-wavelength magnons which is expected from the random spatial distribution of Mn atoms in the Bi planes. A detailed analysis of the INS provides the average values for exchange couplings which are consistent with reports of carrier-mediated interactions.

The effects of grain size on magnetic and mechanical properties of Dy-free Nd-Fe-B sintered magnets were studied. The grain size of the sintered magnets was varied by using different sized Dy-free Nd-Fe-B alloy feedstock powders which were ball milled to different extents. Increasing the ball milling time from 7 to 11 h caused the average particle size of the powders to decrease from 3.6 to 2.1 µm, while the average grain size of the corresponding sintered magnets decreased from 5.0 to 4.0 µm. The intrinsic coercivity Hcj and maximum energy product (BH)max of these magnets increased from 11.6 to 13.7 kOe and 41.6 to 43.6 MGOe, respectively. The finer grain magnets exhibited better thermal stability, as indicated by a smaller temperature coefficient of Hcj (−0.71%/°C). With extending ball milling time to 15 h, the magnetic properties of the magnets deteriorate, while the flexural strengths first decrease and then increase. The flexural strength improvement is attributed to the increased Oxygen content in the magnets due to finer grains. The coercivity enhancement by reduction of grain size is a promising approach to develop Dy-free Nd-Fe-B sintered magnets with better thermal stability. It is important to control the Oxygen contents in the magnets to compromise both magnetic and mechanical properties.

Compared to the widely used Fe-3.2wt%Si steel, Fe-6.5wt%Si has superior electric and magnetic properties, including higher electrical resistivity, lower iron loss, higher permeability, and near zero magnetostriction. However, Fe-6.5wt%Si sheet is difficult to produce using traditional manufacturing processes as the high silicon content favors the formation of ordered phases that embrittle the material. Fortunately, these ordered phases can be suppressed if the alloy is cooled fast enough from a high temperature kinetically trapping the disordered solid solution or amorphous state. Planar flow casting is known for its rapid solidification rate. In order to consider it as a viable method to manufacture ductile Fe-6.5wt%Si sheets, the effect of cooling rate on physical properties of Fe-6.5wt%Si alloy are systematically investigated. In this work, various cooling rates are achieved by changing melt-spin wheel speeds, which significantly affect the solidification temperature profile and have profound effects on ordering, microstructures, textures, hardness, and magnetic properties. High cooling rates result in refined grains, reduced ordering, enhanced out of the plane texture, decreased hardness, and increased coercivity. This study shows a critical cooling rate at ~1.7 × 105 K/s, corresponding to a tangential wheel speed of 5-7 m/s, below which the hardness significantly increases in agreement with the sudden increase of the ordered phases that causes the material embrittlement.

New determination of the magnetic anisotropy from single crystals of ( Fe 1 - x Co x ) 2 B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with x = 0.3 - 0.35 are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, and Ti additions. Previous attempts at developing a significant hysteresis have been unsuccessful in this system. Our melt-spinning experiment indicates that this system shows rapid crystallization.

Fine Alnico 8 spherical powder produced by gas atomization was consolidated through hot pressing (HP), hot isostatic pressing (HIP), and compression molding and subsequent sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were analyzed and compared. The HP, HIP, and CMS magnets exhibited different features in microstructures and magnetic properties. Magnetically annealed at 840 °C for 10 min and subsequently tempered at 650 °C for 5 h and 580 °C for 15 h, the HIP sample achieved the best coercivity ( $H_{\mathrm {cj}} =1845$ Oe) due to spinodally decomposed (SD) phases with uniform and well-faceted mosaic morphology. The CMS sample had a lower $H_{\mathrm {cj}}$ than HIP and HP samples, but a higher remanence and thus the best energy product (6.5 MGOe) due to preferential grain alignment induced by abnormal grain growth.

Vacuum sintering has been found to result in large decrease in the electrical resistivity of cobalt ferrite samples which led to the enhancement of the thermoelectric properties compared to samples prepared by other methods. Magnetization of the sample was found to be affected by a (Co1-xFex)O phase developed due to the reducing nature of the vacuum chamber in which the samples were sintered. The Curie temperature obtained for the samples is similar.

SiO2 coated Fe3O4 submicrometer spherical particles (a conducting core/insulating shell configuration) are fabricated using a hydrothermal method and are loaded at 10 and 20 vol % into a bisphenol E cyanate ester matrix for synthesis of multifunctional composites. The dielectric constant of the resulting composites is found to be enhanced over a wide frequency and temperature range while the low dielectric loss tangent of the neat cyanate ester polymer is largely preserved up to 160 °C due to the insulating SiO2 coating on individual conductive Fe3O4 submicrometer spheres. These composites also demonstrate high dielectric breakdown strengths at room temperature. Dynamic mechanical analysis indicates that the storage modulus of the composite with a 20 vol % filler loading is twice as high as that of neat resin, but the glass transition temperature considerably decreases with increasing filler content. Magnetic measurements reveal a large saturation magnetization and negligibly low coercivity and remanent magnetization in these composites.

Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D03 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speed during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D03 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ∼100 μm at 1m/s to ∼8 μm at 30m/s, which lead to changes in coercivity.

A brief review of the current literature concerning compounds based upon the R 5 (Si x Ge 1− x ) 4 structure reveals that essentially all examined alloys contain “linear features” similar to those first observed by Szade et al. on the surface of Gd 5 Si 4 , Gd 5 Si 2 Ge 2 and Gd 5 Ge 4 samples. Attempts to characterize these features, using a variety of techniques, have proven to be a difficult task. Rather than becoming clearer and better understood, discrepancies in the reported data have resulted in much confusion. A series of comprehensive experiments involving optical, scanning and transmission electron microscopy, X-ray diffractometry, magnetization, and heat capacity measurements have been performed in an attempt to clarify the situation. These experiments, coupled with a critical examination of published data, allow certain misconceptions and apparent contradictions to be understood and explained. Of major importance is the discovery that the volume fraction of the linear feature present is far lower than what one may estimate on the basis of etched samples. The results of this study support previous data that show the linear features are a second phase of composition R 5 (Si x Ge 1− x ) 3 , and reveal the various difficulties associated with proper identification of this phase due to its small size scale and low volume percentage.

Here, a neutron powder diffraction (NPD) study of LnMnSbO (Ln = La or Ce) reveals differences between the magnetic ground state of the two compounds due to the strong Ce-Mn coupling compared to La-Mn. The two compounds adopt the P4/nmm space group down to 2 K, and whereas magnetization measurements do not show obvious anomaly at high temperatures, NPD reveals a C-type antiferromagnetic (AFM) order below TN = 255K for LaMnSbO and 240 K for CeMnSbO. While the magnetic structure of LaMnSbO is preserved to base temperature, a sharp transition at TSR = 4.5K is observed in CeMnSbO due to a spin-reorientation (SR) transition of the Mn2+ magnetic moments from pointing along the c axis to the ab plane. The SR transition in CeMnSbO is accompanied by a simultaneous long-range AFM ordering of the Ce moments, which indicates that the Mn SR transition is driven by the Ce-Mn coupling. The ordered moments are found to be somewhat smaller than those expected for Mn2+ (S = 5/2) in insulators, but large enough to suggest that these compounds belong to the class of local-moment antiferromagnets. The lower TN found in these two compounds compared to the As-based counterparts (TN = 317 formore » LaMnAsO, TN = 347K for CeMnAsO) indicates that the Mn-Pn (Pn=As or Sb) hybridization that mediates the superexchange Mn-Pn-Mn coupling is weaker for the Sb-based compounds.« less

In this article, we study the relationship between precipitate morphology and superconductivity in KxFe1.6+ySe2 single crystals grown by self-flux method. Scanning electron microscopy (SEM) measurements revealed that the superconducting phase forms a network in the samples quenched above iron vacancy order-disorder transition temperature Ts, whereas it aggregates into micrometer-sized rectangular bars and aligns as disconnected chains in the furnace-cooled samples.

The Ni-Pr phase diagram on the Pr-rich side was revised using differential thermal analysis, differential scanning calorimetry, and scanning electron microscopy. The existence of four stoichiometric compounds, Ni2Pr, NiPr, Ni3Pr7, and NiPr3, was confirmed; however, the melting temperatures of 766 °C (NiPr), 566 °C (Ni3Pr7), and 562 °C (NiPr3) are considerably different from the previously reported values. The same was true for the four eutectic reactions, which were determined to be as follows: liquid (L) (45±1 at.% Pr) ↔ Ni2Pr+NiPr at a mean temperature of 732±5 °C; L (65±1 at.% Pr) ↔ NiPr+Ni3Pr7 at a mean temperature of 550±2 °C; L (72±2 at.% Pr) ↔ Ni3Pr7+NiPr3 at a mean temperature of 557±2 °C; and L (77±1 at.% Pr) ↔ NiPr3+Pr.

We report evidence of the absence of zero thermal expansion in well-characterized high-quality polycrystalline samples of YbGaGe. High-quality samples of YbGaGe were produced from high-purity starting elements and were extensively characterized using X-ray powder diffraction, differential thermal analysis, atomic emission spectroscopy, magnetization, and neutron powder diffraction at various temperatures. Our sample melts congruently at 920 ∘C. A small amount of Yb2O3 was found in our sample, which explains the behavior of the magnetic susceptibility. These observations rule out the scenario of electronic valence driven thermal expansion in YbGaGe. Our studies indicate that the thermal expansion of YbGaGe is comparable to that of Cu.

Selected rare-earth (RE)-based δ-phase compounds of the composition RE 6 Fe 13− x Al 1+ x (1 ≤ x ≤ 4) have been prepared and studied to ascertain their role in conveying coercivity to the so-called ferromagnetic bulk metallic glass (BMG) alloys (RE) 60 Fe 30 Al 10 . It was found that δ-phase does not exist for RE = Sm or Gd. However, nearly single δ-phase Pr-based compounds of the composition Pr 6 Fe 13− x Al 1+ x in a range of Al concentration 1.5 ≤ x ≤ 3.5 were successfully synthesized. The antiferromagnetic behavior of the Pr-based δ-phase compounds is clearly seen from temperature-dependent magnetization measurements and the Neel temperature shows a quasi-linear decrease from 320 K to 115 K as x in Pr 6 Fe 13− x Al 1+ x is increased from 1 to 4. The observed Al-concentration dependence of the Pr 6 Fe 13− x Al 1+ x Neel temperatures is expected to be reflected in the magnetic behavior of the BMG alloys of composition Pr 60 Fe 30 Al 10 .

The crystal structure of the hexagonal Zn3MgY Phase has been determined by single-crystal X-ray diffraction. The structural model, refined to a final R value of 0.047, has the composition Zn60.68Mg18.28Y21.04. a = 9.082(2) Angstrom and c = 9.415(5) Angstrom and the space group P6(3)/mmc. Among the 36 atomic sites 28 (or 77.8%) are icosahedrally coordinated (heavily distorted by the large Y atoms) and occupied by Zn and Mg (not all) atoms. As the interatomic distance between the centers of a pair of icosahedra increases from 2.6 to 3.1 Angstrom, 4.7 to 4.8 Angstrom, to 6.4 Angstrom, their connection changes from interpenetration, face-sharing, to vertex-sharing. The structure of Zn3MgY is characterized by a layer structure consisting of FP(FP)' layers stacked along the c axis, where F and P denote flat and puckered layers, respectively, and (FP)' is related to FP by a 6(3) screw. The Zn3 icosahedra, in the PFP' layer block, are fused into pairs in the directions. On the other hand the Zn 1, Zn2, and Mg/Zn icosahedra form vertex-sharing, face-sharing, or interpenetrated chains in the [001] direction. (C) 2003 Elsevier B.V. All rights reserved.

Sm–Fe-based alloys were produced by melt spinning with various melt spinning parameters and alloying additions. The structural and microstructural evolution varied and strongly depended on processing and alloy composition. The microstructural scale was found to vary from micron to nanometer scale depending on the solidification rate and alloying additions. Additions of Si, Ti, V, Zr and Nb with C were all found to refine the scale, and the degree of refinement was dependent on the atomic size of the alloying agent. The alloying was also found to affect the dynamical aspects of the melt spinning process, although in general the material is characterized by a poor melt stream and pool, which in part contributes to the microstructural variabilities. The alloying additions also suppressed the long-range ordering, leading to formation of the TbCu 7 -type structure. The ordering was recoverable upon heat treatment, although the presence of alloying agents suppressed the recovery process relative to the binary alloy. This was attributed to the presence of Ti (V, Nb, Zr) in solid solution, which limited the diffusion kinetics necessary for ordering. In the binary alloy, the ordering led to the development of antiphase domain structures, with the antiphase boundaries effectively pinning Bloch walls.

Anisotropic magnets were fabricated by a vacuum hot deformation (VHD) method from isotropic MRE2(Fe,Co)14B ribbons mixed with Zn powder (MRE = Nd + Y + Dy). TEM microstructure shows that the VHD processing results in the formation of aligned platelet-like grains perpendicular to the pressing direction, and thus produces a strong magnetic anisotropy texture parallel to the pressing direction. The addition of Zn is helpful to develop higher magnetic anisotropy and retain better magnetic properties during the VHD processing. An optimized VHD magnet obtained a (BH)max of 23.3 MGOe compared to 9.6 MGOe for the isotropic ribbons. The temperature coefficients of Mr and Hc for the VHD sample are -0.09 and -0.48%/°C in the temperature range of 27-127°C, respectively.

Structure and magnetic properties of high-quality polycrystlline CeMnAsO, a parent compound of the "1111"-type oxypnictides, have been investigated using neutron powder diffraction and magnetization measurements. We find that CeMnAsO undergoes a C-type antiferromagnetic order with Mn$^{2+}$ ($S=5/2$) moments pointing along the \textit{c}-axis below a relatively high N\'{e}el temperature of $T_{\rm N} = 345$ K. Below $T_{\rm SR} = 35$ K, two instantaneous transitions occur where the Mn moments reorient from the $c$-axis to the \textit{ab}-plane preserving the C-type magnetic order, and Ce moments undergo long-range AFM ordering with antiparallel moments pointing in the \textit{ab}-plane. Another transition to a noncollinear magnetic structure occurs below 7 K. The ordered moments of Mn and Ce at 2 K are 3.32(4) $\mu_{B}$ and 0.81(4)$\mu_{B}$, respectively. We find that CeMnAsO primarily falls into the category of a local-moment antiferromagnetic insulator in which the nearest-neighbor interaction ($J_{1}$) is dominant with $J_{2}, Comment: 8 pages, 6 figures, two tables, 38 references, Physical Review B, Accepted and in production

Large high-quality single crystals of hole-doped iron-based superconductor (Ba1-xKx)Fe2As2 were grown over a broad composition range 0.22

Mechanical processing of polycrystalline LiAlH4 in the presence of titanium- and iron-based catalysts induces the transformation of LiAlH4 into Li3AlH6, Al and H2 at room temperature. Several catalysts were tested and it was established that their activity gradually decreases from TiCl4 to Fe in the series TiCl4>Al3Ti≫Al22Fe3Ti8>Al3Fe>Fe. The high catalytic activity of TiCl4 has been attributed to microcrystalline intermetallic Al3Ti, which rapidly forms in situ from TiCl4 and LiAlH4 during mechanical processing and then acts as a heterogeneous dehydrogenation catalyst.

The need for non-contact torque sensors has sparked considerable interest in developing new magnetomechanical sensor materials [1, 2, 3, 4, 5]. Highly magnetostrictive materials, such as Terfenol (Tb0.3Dy0.7Fe2) [6], SmFe2 [7] and other rare-earth-iron compounds have been considered as candidates for such applications. These materials have very high saturation magnetostrictions (1000–3000ppm) [6], and might reasonably be expected to have high sensitivity of magnetization to stress and therefore be suitable for magnetomechanical sensor applications. Maraging steel has been considered an alternative sensor material by Garshelis [2]. Co-ferrite and metal-bonded Co-ferrite composites have recently been investigated by the authors as an alternative to existing materials competing for use in automotive and other torque sensing applications. The materials are inexpensive and non-corroding, and the metal-bonded Co-ferrite composites are mechanically robust and can be attached (e.g. by brazing) to metal parts. They show a steep slope of magnetostriction at low applied fields, (dλ/dH)σ, which contributes to a high sensitivity of magnetic induction to stress, hence giving high signal-to-background noise ratios in sensor applications.

Mechanochemical processing of polycrystalline LiAlH4 revealed good stability of this complex aluminohydride during high-energy ball-milling in a helium atmosphere for up to 35 h. The decomposition of lithium aluminohydride into Li3AlH6, Al and H2 is observed during prolonged mechanochemical treatment for up to 110 h and is most likely associated with the catalytic effect of a vial material, iron, which is introduced into the hydride as a contaminant during mechanical treatment.

Melt-spun ribbons of Nd–Fe–B modified with Au and/or Cu have been investigated as a function of both composition and cooling rate. When added to stochiometric Nd2Fe14B (2–14–1), Au resulted in the formation of NdAu at the expense of the 2–14–1 phase. The addition of Nd(Au1−xCux) to the stochiometric material (Nd2Fe14B)95+Nd2.5 (Au1−xCux)2.5 (x=0–0.3) results in a novel two phase microstructure. As spun alloys solidified at higher wheel speeds (≥25 m/s) contain a two-phase structure consisting of an amorphous Nd–Fe–B matrix with embedded Nd(Au1−xCux) nanophase spheres. The structure of nanocrystalline particles has been characterized with X-ray diffraction, electron microdiffraction and energy dispersive spectroscopy. The formation mechanism of this novel structure evolution under different compositions and processing parameters is discussed.

The temperature dependence of the magnetic anisotropy of magnetoelastic chromium-substituted cobalt ferrites (CoCrxFe 2-xO4 with 0 les x les 0.8) was investigated over the temperature range 10-400 K. The first-order cubic anisotropy coefficient K1 was calculated by fitting the high-field regimes of the major hysteresis loops to the law of approach to saturation, which is based on the assumption that at sufficiently high field only rotational processes remain. It was found that anisotropy increases substantially with decreasing temperature from 400 to 150 K. Below 150 K, it appears that even under a maximum applied field of 5 T, the anisotropy of CoFe2O4 and CoCr0.2Fe 1.8O4 is so high that it prevents complete approach to saturation. In general, at fixed temperature the magnetic anisotropy decreases with increasing Cr content, which could be explained based on the one-ion model and the results of Mossbauer studies: According to the one-ion anisotropy model, Co2+ ions in octahedral sites of the spinel structure are responsible for the high anisotropy of cobalt ferrite, and substitution of Cr3+ for Fe 3+ appears to displace Co2+ ions from octahedral sites to tetrahedral sites

The phase relationships at the Gd-rich end of the Gd-C system were established. The addition of C expands the lattice parameters of pure Gd, indicating that C dissolves in Gd, but the solid solubility of C is less than 2 at.% below 600°C. Below 600°C the ‘Gd2C’ phase appears to exist as a line compound, but exhibits a narrow solid solution region above this temperature. This phase is slightly C deficient, i.e. Gd2C1−x, where x=0.015 [Gd2C0.985]. ‘Gd2C’ has the rhombohedral C19, CdCl2-type structure with a=6.29 A and α=33.70°. The Gd-C alloys are quite reactive in moist air, forming gaseous hydrocarbons and a white powder which flakes off of the metallic ingots, and must be handled in glove boxes. Magnetic measurements indicated that ‘Gd2C’ orders ferromagnetically at 350°C. This is the highest known magnetic ordering temperature for any binary lanthanide compound which does not contain Fe or Co.

Precipitation behavior of second phases from Gd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7/ solid solution was studied by processing in low oxygen partial pressure. With the decrease of solid solubility in the low oxygen partial pressure, Gd/sub 2/BaCuO/sub 5/ and CuO were precipitated from the solid solution as second phases. This resulted in an increase in the superconducting transition temperature up to that of GdBa/sub 2/Cu/sub 3/O/sub 7/ and an enhancement in the critical current density. The amount and size of the second phases can be controlled by the oxygen partial pressure, processing temperature and the starting composition, thus providing a useful method to introduce flux pinning centers for the improvement of critical current density.

Thermal expansion and magnetostriction of polycrystalline Pr/sub 5/Ni/sub 2/Si/sub 3/ and Pr/sub 15/Ni/sub 7/Si/sub 10/ samples are investigated over the temperature range of 5 to 300 K. The results indicate that there are two kinds of magnetic phase transitions in the material, one corresponding to the Curie temperature (49 K) and the other at a lower temperature (26 K) exhibiting characteristics of a spin reorientation transition. The higher transition temperature marks the onset of ferromagnetic order. The second transition is associated with the appearance of an inflection point in both the magnetization (M) vs magnetic field (H) and /spl lambda/ vs H curves. Positive magnetostriction at all temperatures and the inflection point in the /spl lambda/-H curve is observed at the same magnetic field and temperature as in the M vs. H curve.

The effect of Nd substitution on microstructure and magnetic properties in [Nd/sub x/(YDy)/sub 0.5(1-x)/]/sub 2.2/Fe/sub 14/B ribbons melt-spun at 22 m/s has been systematically studied. As-spun ribbons with low Nd content consist of 2 : 17 and 2 : 14 : 1 phases in an amorphous matrix, while as-spun ribbons with high Nd contain 2 : 14 : 1 and Fe phases in the amorphous matrix. After annealing at 700/spl deg/C for 15 min, all of the ribbons exhibit only a single 2 : 14 : 1 phase in their X-ray diffraction patterns. Nd substitution can improve the maximum energy product of annealed ribbons but deteriorate the temperature stability of the ribbons. Increasing Nd (x) from 0 to 0.8, decreases coercivity from 22 to 13.5 kOe, but increases the maximum energy product from 5.87 to 11.2 MGOe. The temperature coefficients for remanence and coercivity increase from -0.045/spl deg/C to -0.106 %//spl deg/C, and -0.306 to -0.38 %//spl deg/C, respectively for the same substitution range. Transmission electron microscope microstructures show that the samples with less Nd content exhibit a more uniform distribution of grains. Their average grain size is about 40 nm. The studied results show that the YDy-based R/sub 2/Fe/sub 14/B magnets are very promising for high-temperature performance.

Examples of stable binary icosahedral quasicrystals are relatively rare, and at present there are no known examples featuring localized magnetic moments. These would represent an ideal model system for attaining a deeper understanding of the nature of magnetic interactions in aperiodic lattices. Here we report the discovery of a family of at least seven rare earth icosahedral binary quasicrystals, i-R-Cd (R = Gd to Tm, Y), six of which bear localized magnetic moments. Our work highlights the importance of carefully motivated searches through phase space and supports the proposal that, like icosahedral Sc12Zn88 (ref. ), binary quasicrystalline phases may well exist nearby known crystalline approximants, perhaps as peritectically forming compounds with very limited liquidus surfaces, offering very limited ranges of composition/temperature for primary solidification.

Unlike Y123 which forms only a stochiometric compound, the light rare earth elements (LRE) form a solid solution LRE1+xBa2-xCu3O7+δ (LRE123ss), with increasing substitution of the LRE3+ for the Ba2+ with increasing ionic radii of the LRE. Charge balance is maintained by increasing oxygen occupation on the anti-chain sites. The range of solubility is partially controlled by the oxygen partial pressure (PO2). The peritetic decomposition temperature also increases with increasing ionic radii. At doping levels of 0 > × > 0.1, there is an increase in Tc when the high temperature annealing (T ∼ 940‡C) is performed in low PO2 (> 0.1 bar). The maximum Tc occurs at a doping level of ∼x < 0.05 for Nd and Gd. When annealing is performed in 1 bar PO2, there is a gradual decrease in Tc with increasing x. These phenomenon can be understood in terms of the number and distribution of the LRE which substitute on the Ba site.

Powders of YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) and compositions around Y123 were heated by a containerless process and melt-spun in 21% oxygen atmosphere at temperatures of 1400/spl deg/C to 1650/spl deg/C. Homogeneous materials were obtained with micron and submicron crystalline phases uniformly dispersed in an amorphous matrix. For Y123, the crystalline phases are identified by XRD as BaCu/sub 2/O/sub 2/ and Y/sub 2/O/sub 3/ when the melt-spinning temperature is below 1600/spl deg/C. At 1650/spl deg/C, the crystalline phases are Y/sub 4/Ba/sub 3/O/sub 9/, BaCu/sub 2/O/sub 2/ and Y/sub 2/O/sub 3/. The phase composition of the solidified melt is directly related to the oxygen content of the melt and can be related to the equilibrium phase diagrams at lower oxygen partial pressures. Isothermal annealing in oxygen at temperatures 500/spl deg/C to 950/spl deg/C reveals that the crystallization sequence is: Y123 begins to form at 500/spl deg/C, Y123 with minor amount of Y/sub 2/BaCuO/sub 5/ at 800/spl deg/C, Y123 with very minor amount of CuO at 900/spl deg/C, and single phase Y123 at 950/spl deg/C. >

Modified high-pressure gas atomization (HPGA) produces spherical, rapidly solidified powder, which is more suitable for bonded magnet processing. He atomization produced powder in the diameter

We study the relationship between precipitate morphology and superconductivity in K${}_{x}$Fe${}_{1.6+y}$Se${}_{2}$ single crystals grown by self-flux method. Scanning electron microscopy (SEM) measurements revealed that the superconducting phase forms a network in the samples quenched above iron vacancy order-disorder transition temperature ${T}_{s}$, whereas it aggregates into micrometer-sized rectangular bars and aligns as disconnected chains in the furnace-cooled samples. Accompanying this change in morphology the superconducting shielding fraction is strongly reduced. By post-annealing above ${T}_{s}$ followed by quenching in room temperature water, the network recovers with a superconducting shielding fraction approaching 80$%$ for the furnace-cooled samples. A reversible change from network to bar chains was realized by a secondary heat treatment in annealed samples showing a large shielding fraction, that is, heating above ${T}_{s}$ followed by slow cooling across ${T}_{s}$. The large shielding fraction observed in K${}_{x}$Fe${}_{1.6+y}$Se${}_{2}$ single crystals actually results from an uniform and contiguous distribution of superconducting phase. Through the measurements of temperature dependent x-ray diffraction, it is found that the superconducting phase precipitates while the iron vacancy ordered phase forms together by cooling across ${T}_{s}$ in K${}_{x}$Fe${}_{1.6+y}$Se${}_{2}$ single crystals. It is a solid solution above ${T}_{s}$, where iron atoms randomly occupy both Fe1 and Fe2 sites in the iron vacancy disordering status; and phase separation is driven by the iron vacancy order-disorder transition upon cooling. However, neither additional iron in the starting mixtures nor as-quenching at high temperatures can extend the miscibility gap to the KFe${}_{2}$Se${}_{2}$ side.

Single crystals of CaNi${}_{2}$ and CaNi${}_{3}$ are successfully grown out of excess Ca. Both compounds manifest a metallic ground state with enhanced, temperature-dependent magnetic susceptibility. The relatively high Stoner factors of $Z=0.79$ and $0.87$ found for CaNi${}_{2}$ and CaNi${}_{3}$, respectively, reveal their close vicinity to ferromagnetic instabilities. The pronounced field dependence of the magnetic susceptibility of CaNi${}_{3}$ at low temperatures ($Tl25$ K) suggests strong ferromagnetic fluctuations. A corresponding contribution to the specific heat with a temperature dependence of ${T}^{3}$ln$T$ is also observed.

In order to probe the changes in the valence state and magnetic properties of Eu metal under extreme pressure, x-ray absorption near-edge spectroscopy, x-ray magnetic circular dichroism and synchrotron Mossbauer spectroscopy experiments have been carried out. The Mossbauer isomer shift exhibits an anomalous pressure dependence, passing through a maximum near 20 GPa. Density functional theory has been applied to give insight into the pressure-induced changes in both Eu’s electronic structure and Mossbauer isomer shift. Contrary to previous reports, Eu is found to remain nearly divalent to the highest pressures reached (87 GPa) with magnetic order persisting to at least 50 GPa. These results should lead to a better understanding of the nature of the superconducting state found above 75 GPa and of the sequence of structural phase transitions observed to 92 GPa.

Previous work has shown that unlike YBa2 Cu3 O7-δ (Y123), the Nd-Ba-Cu-O system exhibits a solid solution Nd1+xBa2-x Cu3O7+δ (Nd123ss) for 0.04≤ × ≤0.6.1–3) An earlier paper showed that although the superconducting properties decrease nonlinearly for increasing x, Tc can be varied by increasing the annealing temperature without changing the low temperature oxygen soak.2 The changes in microstructure and Tc with increasing x are analogous with Y123 with increasing δ except that the total hole concentration remained constant. Tc was modeled in terms of oxygen disorder resulting from Nd3+ atoms on the Ba sites relocating chain oxygens to anti-chain sites. The variability in Tc as a function of x and processing conditions can be explained by the number of fourfold coordinated coppers on the chain sites. In this paper, the model has been further substantiated by processing in 1% O2. The annealing in a reduced oxygen partial pressure followed by a 450°C oxygen soak resulted in a marked increase in Tc compared to the 100% PO2 anneal. The low PO2 anneal favors pairing of Nd3+ substituting for Ba2+ to conserve oxygen ions, resulting in fewer disrupted fourfold-coordinated coppers thus increasing charge transfer from the planes to the chains.

Using a novel melt-spinning technique, the authors have produced both amorphous and nanocrystalline NdBa/sub 2/Cu/sub 3/O/sub 7-x/ and GdBa/sub 2/Cu/sub 3/O/sub 7-x/ materials. Samples melt-spun in O/sub 2/ consist of nanocrystals with the tetragonal 123 structure while those processed in N/sub 2/ show an amorphous matrix with small amounts of crystalline BaCu/sub 2/O/sub 2/, as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. The difference is due to the strong dependence of the phase relations on the O/sub 2/ partial pressure. Superconductivity can be fully restored by heating above 1000 degrees C followed by a 450 degrees C anneal in O/sub 2/. High-temperature XRD studies show that the 123 phase crystallizes directly from the amorphous matrix below 800 degrees C. Restoration of the orthorhombic 123 phase does not necessarily ensure good superconducting properties, a result attributed to disorder on the heavy metal sites. >

Results obtained from detailed studies of the microstructure and devitrification behavior, as revealed by advanced electron microscopy and synchrotron x-ray diffraction techniques, were compared with magnetic and thermal analysis characterization to obtain insight into the appreciable coercivity of nominally-amorphous melt-spun ribbon of Nd/sub 60-2/3x/Fe/sub 30-1/3x/Al/sub 10+x/(-2

Nd/sub 6/Fe/sub 13-x/Al/sub 1+x/, (/spl delta/) is a complex antiferromagnet with a Neel temperature that ranges from /spl sim/250 K to /spl sim/350 K. Studies of polycrystalline samples of the Nd compound have shown that the material undergoes a series of metamagnetic transitions as a function of magnetic field. In the present study, single crystals of /spl delta/ have been grown and characterized. Low temperature magnetization studies demonstrate that there are a number of competing magnetic interactions in the material, which have different temperature dependencies. As a result, for a narrow range of fields, the /spl delta/ crystals exhibit unique reentrant magnetization versus temperature behavior.

The structural and magnetic phase transitions have been studied on NdFeAsO single crystals by neutron and x-ray diffraction complemented by resistivity and specific heat measurements. Two low-temperature phase transitions have been observed in addition to the tetragonal-to-orthorhombic transition at T_S = 142 K and the onset of antiferromagnetic (AFM) Fe order below T_N = 137 K. The Fe moments order AFM in the well-known stripe-like structure in the (ab) plane, but change from AFM to ferromagnetic (FM) arrangement along the c direction below T* = 15 K accompanied by the onset of Nd AFM order below T_Nd = 6 K with this same AFM configuration. The iron magnetic order-order transition in NdFeAsO accentuates the Nd-Fe interaction and the delicate balance of c-axis exchange couplings that results in AFM in LaFeAsO and FM in CeFeAsO and PrFeAsO.

We report the discovery of a binary icosahedral phase in a Sc-Zn alloy obtained through solution-growth, producing millimeter-sized, facetted, single grain quasicrystals that exhibit different growth morphologies, pentagonal dodecahedra, and rhombic triacontahedra, under only marginally different growth conditions. These two morphologies manifest different degrees of quasicrystalline order. The discovery of i-Sc{sub 12}Zn{sub 88} suggests that a re-examination of binary phase diagrams at compositions close to crystalline approximant structures may reveal other binary quasicrystalline phases.

Metal-bonded cobalt ferrite composites are promising candidates for torque sensors and other magnetostrictive sensing and actuating applications. In the present study, the temperature dependence of the magnetomechanical effect in a ring-shape cobalt ferrite composite under torsional strain has been investigated in the temperature range of −37 to 90 °C. The changes of external axial magnetic field were measured as a function of applied torque. Magnetomechanical sensitivity of ΔHext/Δτ=65 A N−1 m−2 was observed with a magnetomechanical hysteresis of Δτ=±0.62 N m at room temperature (22 °C). These were then measured as a function of temperature. Both decreased as the temperature increased throughout the entire range. The magnetomechanical hysteresis became negligible at temperatures higher than 60 °C, above which there was a linear change in external magnetic field with applied torque. These temperature dependences are explained by the changes of magnetostriction, anisotropy, spontaneous magnetization, and p...

The ternary intermetallic compound, ${\text{Pr}}_{6}{\text{Ni}}_{2}{\text{Si}}_{3}$, is a member of a structure series of compounds based on a triangular structure where the number of Pr atoms in the prism cross section can be systematically varied. ${\text{Pr}}_{6}{\text{Ni}}_{2}{\text{Si}}_{3}$ contains two distinct Pr lattice sites which result in complex interactions between the magnetic ions. Extensive measurements of specific heat and magnetization on single-crystal samples indicate that ${\text{Pr}}_{6}{\text{Ni}}_{2}{\text{Si}}_{3}$ orders with both a ferromagnet and an antiferromagnet component, with ordering temperatures of 39.6 and $\ensuremath{\sim}32\text{ }\text{K}$, respectively. The ferromagnetic component $\ensuremath{\parallel}$ $c$ axis is accompanied by a large hysteresis, and the antiferromagnetic component $\ensuremath{\perp}$ $c$ axis is accompanied by a spin-flop-type transition. More detailed measurements, of the vector magnetization, indicate that the ferromagnetic and the antiferromagnetic order appear independent of each other. These results not only clarify the behavior of ${\text{Pr}}_{6}{\text{Ni}}_{2}{\text{Si}}_{3}$ itself but also of the other members of the structure series, ${\text{Pr}}_{5}{\text{Ni}}_{2}{\text{Si}}_{3}$ and ${\text{Pr}}_{15}{\text{Ni}}_{7}{\text{Si}}_{10}$.

Magnetization, resistivity, and specific heat measurements were performed on solution-grown single crystals of six $\text{Gd}{T}_{2}{\text{Zn}}_{20}$ ($T=\text{Fe}$, Ru, Os, Co, Rh, and Ir) compounds, as well as on their Y analogs. For the Gd compounds, the Fe column members manifest a ferromagnetic (FM) ground state (with an enhanced Curie temperature ${T}_{C}$ for $T=\text{Fe}$ and Ru), whereas the Co column members manifest an antiferromagnetic (AFM) ground state. Thermodynamic measurements on $\text{Y}{T}_{2}{\text{Zn}}_{20}$ revealed that the enhanced ${T}_{C}$ for ${\text{GdFe}}_{2}{\text{Zn}}_{20}$ and ${\text{GdRu}}_{2}{\text{Zn}}_{20}$ can be understood within the framework of Heisenberg moments embedded in a nearly ferromagnetic Fermi liquid. Furthermore, electronic structure calculations indicate that this significant enhancement is due to a large transition metal partial density of states at the Fermi level that places these compounds close to the Stoner FM criterion. The change from FM to AFM ordering (between the Fe and Co column materials) is associated with the filling of electronic states with two additional electrons/f.u. The degree of this sensitivity is addressed by the studies of the pseudoternary compounds $\text{Gd}{({\text{Fe}}_{x}{\text{Co}}_{1\ensuremath{-}x})}_{2}{\text{Zn}}_{20}$ and $\text{Y}{({\text{Fe}}_{x}{\text{Co}}_{1\ensuremath{-}x})}_{2}{\text{Zn}}_{20}$, which clearly reveal the effect of $3d$-band filling on their magnetic properties.

The low temperature heat capacity C{sub p} of Fe{sub 1-x}Ga{sub x} alloys with large magnetostriction has been investigated. The data were analyzed in the standard way using electron ({gamma}T) and phonon ({beta}T{sup 3}) contributions. The Debye temperature {Theta}{sub D} decreases approximately linearly with increasing Ga concentration, consistent with previous resonant ultrasound measurements and measured phonon dispersion curves. Calculations of {Theta}{sub D} from lattice dynamical models and from measured elastic constants C{sub 11}, C{sub 12}, and C{sub 44} are in agreement with the measured data. The linear coefficient of electronic specific heat {gamma} remains relatively constant as the Ga concentration increases, despite the fact that the magnetoelastic coupling increases. Band structure calculations show that this is due to the compensation of majority and minority spin states at the Fermi level.

Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi magnets for motor applications. Physical properties other than magnetic ones could significantly affect motor design. Here, we report results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their temperature dependence. A MnBi ingot was prepared using an arc melting technique and subsequently underwent grinding, sieving, heat treatment, and cryomilling. The resultant powders with a particle size of ∼5 μm were magnetically aligned, cold pressed, and sintered at a predefined temperature. Micro-hardness testing was performed on a part of original ingot and we found that the hardness of MnBi was 109 ± 15 HV. The sintered magnets were subjected to compressive testing at different temperatures and it was observed that a sintered MnBi magnet fractured when the compressive stress exceeded 193 MPa at room temperature. Impedance spectra were obtained using electrochemical impedance spectroscopy at various temperatures and we found that the electrical resistance of MnBi at room temperature was about 6.85 μΩ m.