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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.

Replacement of Dy and substitution of Nd in NdFeB-based permanent magnets by Ce, the most abundant and lowest cost rare earth element, is important because Dy and Nd are costly and critical rare earth elements. The Ce, Co co-doped alloys have excellent high-temperature magnetic properties with an intrinsic coercivity being the highest known for T ≥ 453 K.

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.

The solvent-free reaction between o-vanillin and p-toluidine was investigated using NMR, DSC and XRD analyses. At room temperature, o-vanillin and p-toluidine react in a liquid eutectic formed upon grinding, while below 10 °C the same materials appear to react without the formation of a liquid phase, which most likely remains hidden behind solid reactants and reaction products.

Polycrystalline Ni 50 Mn 37 Sn 13 alloy was fully homogenized such that the structural and magnetic transitions were clearly separated from each other in temperature. The sequence of transitions on cooling is: (1) austenite Curie point; (2) austenite to martensite structural and coupled ferromagnetic to paramagnetic transitions (first-order); and (3) martensite Curie point. Most notably, we found the field-induced transformation occurs from paramagnetic martensite to ferromagnetic austenite. The field-induced transition has a temperature dependence of −10 kOe K −1 over a narrow temperature range.

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

Most of the metallic glasses which have been identified to date require rapid solidification processing (RSP) in order to obtain the high cooling rates required to avoid the thermally activated decomposition reactions that result in the formation of crystalline phases. While the free-jet melt spinning technique is commonly used for the investigation of amorphous alloy formation, many of the key process parameters remain poorly understood. In the work presented here, we utilize high speed digital imaging to investigate various melt-pool characteristics and their influence on the melt-spun ribbon. With detailed measurements of melt-pool geometry and surface temperature, we show that the length of this molten zone establishes a critical length scale which characterizes the ribbon thickness and cooling rate. Within certain limits, the ribbon thickness is shown to correlate with a simple 2D laminar flow boundary layer formed at the base of the melt-pool. Estimates of initial quench rate, based on surface temperature measurements, clearly reveal the importance of two distinct cooling periods. The first is the wheel-contact period, where the ribbon remains in intimate contact with the quench wheel and cooling is primarily governed by the heat conduction across the ribbon-wheel boundary. The second is the free-flight period, where the ribbon separates from the wheel, and cooling is governed by radiation and convection into the chamber.

High-energy high-flux synchrotron X-rays have been used to study the spontaneous magnetostriction of R 2 Fe 17 (R=Y, Nd, Gd, Tb, Er) and their carbides in the temperature range 10–1100 K. Addition of interstitial carbon greatly increases both the Curie temperatures ( T C ) and the spontaneous magnetostrain of the compounds, while reduces the anisotropy of the magnetostrain by expanding the distances between rare-earth and neighboring Fe sites. The increase of T C with carbon is due to the increased spatial separation of the Fe hexagon layers. On the basal plane, the Fe hexagons are squeezed and the contribution of Fe sublattice to spontaneous magnetostriction is attenuated, while that of rare-earth sublattice is enhanced. The average bond magnetostrain around Fe sites are in linear relation with their hyperfine field intensities.

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.

Thermal expansion and magnetostriction of members of a homologous series of compounds based on the alloy series Pr(n+2)(n+1)Nin(n?1)+2Sin(n+1) have been measured. The crystal structures of these compounds are closely interrelated because they form trigonal prismatic columns in which the number of trigonal prisms that form the base of the trigonal columns is determined by the value of n in the chemical formula. Two compositions were investigated, Pr5Ni2Si3 and Pr15Ni7Si10, corresponding to n=3 and n=4, respectively. The results were analyzed and used to determine the location of magnetic phase transitions by calculating the magnetic contribution to thermal expansion using the Gruneisen–Debye theory. This allowed more precise determination of the magnetic transition temperatures than could be achieved using the total thermal expansion. The results show two phase transitions in each material, one corresponding to the Curie temperature and the other at a lower temperature exhibiting characteristics of a spin reorientation transition.

Detailed structural and magnetic characterization was carried out on nominally amorphous melt-spun ribbon based on the composition Nd 60 Fe 30− x Al 10+ x to pursue the origins of its anomalously large coercivity values. The combined structural and magnetic analyses point to the existence of antiferromagnetic motes within the melt-spun ribbon. The average diameter of these motes is 1.2±0.5 nm and their crystal structure is related to the Nd 6 Fe 13− x Al 1+ x , δ -phase structure, which under equilibrium conditions is the primary solidification phase near the Nd 60 Fe 30 Al 10 composition. These motes are hypothesized to strongly couple to the ferromagnetic matrix phase in an “exchange-bias”-type manner and confer extremely high values of coercivity at low temperature. The composition dependence of the δ -phase Neel temperature is reflected in the composition dependence of the onset of large values of coercivity in the melt spun ribbons. The results obtained from melt-spun ribbons are compared to those obtained from a 10 gm drop-cast ingot 6 mm diameter of the same nominal composition and are found to be internally consistent. Delineation of the solidification pathway in the vicinity of the composition RE 60 Fe 30 Al 10 provides a sound physical explanation of the variety of microstructures and associated variety of magnetic behavior found in cast and melt-spun forms of this material.

Thermal expansion anomalies of R2Fe14B (R=Y, Nd, Gd, Tb, Er) stoichiometric compounds were studied by X-ray diffraction with high-energy synchrotron radiation using a Debye–Scherrer geometry in temperature range of ∼10–1000 K. A large invar effect with a corresponding large temperature dependence of lattice parameters ∼10–15 K above their Curie temperatures (Tc) are observed. The a-axes show a larger invar effect than the c-axes in all compounds. The spontaneous magnetostrain of the lattices and bonds are calculated. The iron sublattice is shown to dominate the volumetric spontaneous magnetostriction of the compounds and the contribution from the rare-earth sublattice is roughly proportional to the spin magnetic moment of the rare earths. The bond-length changes are consistent with the theoretical spin-density calculation. The average bonds magnetostrain around Fe sites is approximately proportional to their magnetic moments.

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 effects of the ratio of Y to Dy as well as the effect of Nd and Co substitutions on magnetic properties in [Ndx(YDy)0.5(1-x)]2.2Fe14-yCoyB ribbons melt-spun at 22 m/s have been systematically studied. (Y1-zDyz)2.2Fe14B ribbons with a ratio z of 0.25 or 0.5 simultaneously obtains a smaller temperature coefficient of remanence (α ) and coervicity (β ) which are much smaller than those of Nd-based Nd2Fe14B ribbons. In [Ndx(YDy)0.5(1-x)]2.2Fe14-yCoyB ribbons, Nd substitution (x=0 to 0.8) can improve the maximum energy product (BH)max of annealed ribbons but degrades the temperature stability of the magnetic properties. The ribbons with x=0.4 and y=0 yield a (BH)max of 8.7 MGOe. For these ribbons, the α and β are -0.07 and -0.31 %/°C in the temperature range of 27 to 127°C, respectively. Increasing Co (x) from 0 to 3, slightly decreases coercivity Hcj from 21.5 to 16.3 kOe, but keeps the (BH)max in the range of 8.6 to 10.2 MGOe. The optimal sample with x=0.5 and y=1.5 obtains a (BH)max of 10.2 and 5.0 MGOe at 27 and 250°C, respectively. Its α and β are -0.11 and -0.30 %/°C, respectively. These results show that studied ribbons are very promising to develop into high temperature isotropic bonded magnets capable of operating at or above 180°C.

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.

The growth and characterization of single grains of the primitive icosahedral quasicrystal R–Mg–Cd (R=Y, Gd, Tb or Dy) are described. From the thermodynamic properties, it is confirmed that the system is a spin glass exhibiting the characteristic spin-freezing transition of such systems. There is no evidence for two distinct freezing transitions previously observed for polygrain samples. The bulk magnetic properties and the effect of crystalline electric fields on the spin-freezing temperature are found to be very similar to those of the face-centred icosahedral quasicrystal R–Mg–Zn.

Rapidly solidified (RS) Nd 2 Fe 14 B alloys were prepared by melt-spinning under different melt treatment conditions i.e., the melt temperature was varied prior to ejection onto the quenching wheel. X-ray diffraction, transmission electron microscopy, thermal analysis and magnetic measurement were conducted on the as-quenched alloys to investigate their structural and magnetic characteristics. RS Nd 2 Fe 14 B alloys may display a variety of microstructures depending upon the thermal history of the melt before ejection: it was possible to synthesize an entirely amorphous structure, a partially amorphous structure containing nuclei and/or nanophases and a nanocrystalline structure. The relationship between the formation of crystalline nuclei or nanophases and the thermal history of the melt was studied. A lower melt ejection temperature produced a nanocrystalline microstructure, while higher melt ejection temperatures ( T >1723 K) largely eliminated the presence of nuclei and associated nanophases and produced an amorphous product. The experimental results indicated that optimization of the melt treatment conditions will produce rapidly solidified Nd–Fe–B alloys with a more uniform microstructure.

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.

A complement of experimental characterization techniques – positron annihilation spectroscopy (PAS), transmission electron microscopy, synchrotron X-ray diffraction and elevated temperature ac and dc magnetic measurements – were applied to the study of melt-quenched stoichiometric Nd 2 Fe 14 B ribbons modified by various amounts of the alloying additions Ti and C. These alloying additions are known to enhance the glass-forming ability in Nd 2 Fe 14 B melts, allowing for a wider processing window to produce homogeneous nanoscale materials with tailored magnetic properties. The experimental techniques used in this study reveal the complex multi-phase and multi-scale nature of the ribbons, a result that had escaped detection by lower-resolution techniques. The as-quenched ribbons were found to consist of at least three phases: α-Fe nanocrystals, poorly crystalline Nd 2 Fe 14 B and glass. The measured weight fraction of glass does not show a direct correspondence with quenching wheel speed, a result attributed to the complexity of the melt-spinning heat-transfer process. The Curie temperature of the glassy component of the ribbons varies in a non-systematic way with both Ti and C alloying addition content and wheel speed. PAS provides quantitative measurements of the S (or ‘shape’)-parameter which represents the size of a void or open volume in the material volume probed. The experimental results indicate that an excess of free volume in the glass is associated with increased glass stability, a counterintuitive conclusion. However, the results are consistent with the model of Sietsma and Thijsse [Phys. Rev. B 52 (5) (1995) 3248] who propose that thermal relaxation in glass causes the larger free volume regions in the amorphous structure to break up into smaller voids, which necessarily increases the total number of voids, but decreases the volume per void. This void breakup fosters the processes of cooperative diffusion and subsequent devitrification. It is concluded that the free volume concentration in the amorphous component of melt-spun Nd 2 Fe 14 B alloys produced by the highest quenching wheel speeds and Ti/C alloying addition content is thus not sufficient to allow cooperative diffusion to take place, resulting in an increased stability against devitrification.

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

This paper is focused on understanding hysteresis in Dy3Al2, which is a member of a class of high anisotropy compounds containing high fractions of rare earth elements with no 3-d transition metals. Analysis of the data suggests that the principal domain wall pinning mechanism does not involve the grain boundaries but instead arises from interactions between either the ferromagnetic glass or the ferromagnetic Dy3Al2 phase with the antiferromagnetic DyAl second phase through an exchange bias mechanism.

The phase selection process during solidification of Nd 2 Fe 14 B melt-spun alloys is highly dependent on a few processing parameters. The processing variables that determine the three typical microstructures of melt-spun ribbons are described and a general peritectic rapid solidification model incorporating recalescence is presented.

Systematic electrical transport data are presented for single quasicrystals in the Al–Pd–Re family across the accessible width of formation. The temperature dependence of the electrical conductivity can be accounted for in terms of weak localization and electron-electron interactions for all compositions studied, in contrast with previous studies of cast and annealed polygrain material. These results indicate that the conductivity mechanism in the Al–Pd–Re system is not dramatically different from that of other quasicrystal families.

Nanocrystalline Nd 2 Fe 14 B (2-14-1) exhibits very favorable properties conferred by rapid solidification processes, including: simplified processing, good corrosion resistance and high magnetic hardness provided by a resultant grain size that is on the order of the single-domain size. While the ideal microstructural state of melt-spun 2-14-1 is a homogeneous dispersion of nanocrystallites embedded within a vitrified matrix, in practice it is very difficult to control the microstructural development to a uniform nanocrystalline state. This as-yet unmet challenge underlies the desire to understand, and ultimately to control, the solidification path taken by Nd–Fe–B-based melts during rapid solidification processing in order to obtain a homogeneous microstructure. Processing factors that influence the homogeneity and hence magnetic performance of the rapidly quenched microstructure of Nd 2 Fe 14 B are evaluated and categorized. These results emphasize both the complexities of rapid solidification processing as well as the potential for control of a highly chaotic processing technique. A qualitative solidification model that incorporates recalesence is presented. This model details the evolution of microstructures related to the thermal gradient as well as the phase selection process undertaken during solidification of rapidly solidified Nd–Fe–B alloys. The model is novel in that it explains the observed microstructures, from nanophased equiaxed grains transitioning to large elongated grains, and provides both diagnostic and predictive information concerning rapid solidification processing methods.

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 change of magnetization as a function of applied torque has been investigated for cylindrical rods of 99.9% pure iron, cobalt and nickel. The relationship between the magnetomechanical effect and magnetostriction in these materials has also been investigated. Torque was applied with amplitude up to ±5 N m with no associated bending moment. The magnetic field near the sample surface was measured using a Hall effect sensor at the center of the sample. The results showed a linear dependence of this field on torque once the transient effects of the first few stress cycles had been overcome. The derivative of the surface circumferential magnetic field with respect to torque for a nickel rod was 19 A N −1 m −2 . Cobalt and iron, on the other hand, showed smaller sensitivity to torsional stress, with changes less than 1 A N −1 m −2 . The difference in behavior is due to the higher ratio of magnetostriction to anisotropy in nickel. Magnetostriction measurements were made and it was found that the piezomagnetic coefficient d , that is the slope of the magnetostriction curve d λ /d H , at low magnetic field is an important figure of merit in determining sensitivity of magnetization to torque. It is shown that the sensitivity of magnetic induction to stress d B /d σ is dependent on the ratio of magnetostriction to anisotropy.

Multi-phase microstructures were observed in the psuedo-quaternary phase field of the 2–14–1 magnet materials Nd2Fe14B, Nd2Co14B, Dy2Fe14B, and Dy2Co14B. At equilibrium, (Nd1−yDyy)2(Fe1−xCox)14B had heretofore been widely assumed to be single phase where 1>x>0 and 1>y>0. In this study, three-phase microstructures were observed in (Nd1−yDyy)2(Fe1−xCox)14B when x>0.3 and y>0.5. The Curie temperatures and peritectic decomposition temperatures for Nd2(Fe1−xCox)14B are reported for several values of x in the range 1>x>0.

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.

We did a detailed study on a series of samples of Eu(Ba 1− x R x ) 2 Cu 3 O 7+δ (where R=La, Pr and Eu) by X-ray diffraction, neutron diffraction, magnetic and thermopower measurements. All R 3+ substitutes went to the Ba 2+ site and suppress superconductivity. The suppression of superconductivity does not have a simple relation to the ionic size of the substitutes. On the other hand, the change in crystal structure from orthorhombic to tetragonal has a strong dependence on the ionic size of the substitutes. Pr on Ba site did not cause unexpected structural distortions yet suppress superconductivity at a rate faster than other rare earths. Data of thermopower measurements and neutron diffraction from our rare earth substituted Eu123 samples show that the suppression of superconductivity by Pr on Ba site is electronic, not magnetic in nature.

The dependence of the low-temperature specific heat of ${(\mathrm{L}\mathrm{a}}_{1.85}{\mathrm{Sr}}_{0.15}{)\mathrm{C}\mathrm{u}\mathrm{O}}_{4}$ on magnetic field (H) is reported. Low concentrations of paramagnetic centers allow a different approach to analysis of the data that minimizes the problem of identifying the effects of the line nodes in the energy gap that are expected for d-wave pairing. As a consequence, these effects can be recognized even in the raw data. The data show evidence of the ${T}^{2}$ term expected for $H=0,$ and a well defined ${H}^{1/2}T$ term for $H\ensuremath{\ne}0.$ They conform to a scaling relation recently predicted for d-wave pairing.

New low-temperature specific-heat data for YBa2Cu3O7−δ, 0≤δ≤0.2, and (La1.85Sr0.15)CuO4 in magnetic fields (H) to 9 T are reported. They show features predicted for the lines of nodes in the energy gap that are expected for d-wave pairing; for H=0, a T 2 term; for H≠0 an H 1/2 T term with a crossover to a more complicated T dependence at higher T and lower H. The results are compared with recent measurements in other laboratories.

We report measurements of the dc magnetization, the low-field ac magnetic susceptibility, and the electrical resistivity of large (up to 0.5 ${\mathrm{cm}}^{3}$) single-grain samples of icosahedral $R\ensuremath{-}\mathrm{M}\mathrm{g}\ensuremath{-}\mathrm{Z}\mathrm{n}$ $(R=\mathrm{Y},$ Tb, Dy, Ho, and Er). The dc magnetization and ac magnetic susceptibility data both indicate that icosahedral Tb-Mg-Zn and Dy-Mg-Zn undergo a transition to a spin-glass state at ${T}_{f}=5.8$ and 3.6 K, respectively, while low-temperature ac susceptibility measurements show that ${T}_{f}=1.95$ and 1.3 K for Ho-Mg-Zn and Er-Mg-Zn, respectively. For the series of solid solutions $({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x})\ensuremath{-}\mathrm{M}\mathrm{g}\ensuremath{-}\mathrm{Z}\mathrm{n},$ the freezing temperature ${T}_{f}$ varies approximately as ${x}^{2/3}.$ The $({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x})\ensuremath{-}\mathrm{M}\mathrm{g}\ensuremath{-}\mathrm{Z}\mathrm{n}$ solid solutions have lower ${T}_{f}$ values than $({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x})\ensuremath{-}\mathrm{M}\mathrm{g}\ensuremath{-}\mathrm{Z}\mathrm{n}$ for the same magnetic rare-earth concentrations (x), indicating that local moment anisotropy caused by crystalline electric-field effects plays a significant role in increasing ${T}_{f}.$ On the other hand, angular-dependent studies show that the dc magnetization for $Tg{T}_{f}$ is isotropic within the experimental uncertainty. The electrical resistivity $\ensuremath{\rho}(T)$ of the single-grain samples is only weakly temperature dependent, with a small, negative $d\ensuremath{\rho}/dT.$ Absolute values of the resistivity fall in the range between 150 and 200 \ensuremath{\mu}\ensuremath{\Omega} cm, which is distinctly lower than the values previously reported for other thermodynamically stable icosahedral quasicrystals.