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High-coercivity, c-axis oriented Nd{sub 2}Fe{sub 14}B films grown by molecular beam epitaxy

Description: Thin films of Nd{sub 2}Fe{sub 14}B with a c-axis orientation and bulk- like magnetic properties were grown with thickness as low as 300 {Angstrom}. They were grown on single-crystal MgO(100) wafers overcoated with epitaxial Mo(100) buffer layers. The 2-14-1 phase were crystallized either by sequential deposition or co-deposition of Fe, Nd, and B from pure elemental evaporation sources onto 600-700 C substrates. Structure of each film was characterized in-situ with RHEED and ex-situ with XRD. For the sequentially deposited films, the in-plane saturation field is 60-70 kOe at 300 K, consistent with the bulk anisotropy field of 73 kOe. The spin-reorientation transition at 135 K can also be clearly seen in the in-plane and out-of-plane magnetization vs temperature data. The out-of-plane coercivities range from 15-20 kOe at 20 K and 3-8 kOe at 300 K. Co-deposition results in a multiphase structure, with Nd{sub 2}Fe{sub 14}B now the minority phase. The multiphase structure results in reduced perpendicular anisotropy.
Date: November 1996
Creator: Keavney, D. J.; Fullerton, E. E.; Pearson, J. E. & Bader, S. D.
Partner: UNT Libraries Government Documents Department

Temperature compensation of NdFeB permanent magnets

Description: Permanent magnet blocks of NdFeB have a relatively high maximum energy product. Because of its relatively low Curie temperature, however, NdFeB has a large temperature coefficient for its residual induction. The temperature coefficients of the relative magnetic fields ({Delta}B/B)/{Delta}T in the air gap of NdFeB dipole magnets were reduced from {minus}1.1 {times} 10{sup {minus}3}/c to less than 2 {times} 10{sup {minus}5}/{degree}C under operating temperatures of {+-} 6 C. This was achieved passively by using 1.25-mm-thick strips of 30%-Ni-Fe alloy as flux shunts for the NdFeB blocks. The magnets with soft-steel poles and flux-return yokes were assembled and measured in a temperature-controlled environment.
Date: August 1, 1997
Creator: Kim, S.H. & Doose, C.
Partner: UNT Libraries Government Documents Department

Magnetization reversal in melt-quenched NdFeB

Description: Melt-quenched NdFeB is an important modern permanent magnet material. However, there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQIII compared with MQII and the increased dipolar interactions in MQIII.
Date: April 5, 1999
Creator: Crew, D.C.
Partner: UNT Libraries Government Documents Department

Alloy design of Nd

Description: This report summarizes the results of research conducted as part of CRADA ORNL94-0279 between Oak Ridge National Laboratory and Magnequench International, Inc. The objective was to gain a better understanding of the fracture process in the rare earth based permanent magnets in order to possibly improve the mechanical properties of these inherently brittle intermetallics. The first part of the study established a technique for measuring a critical property, fracture toughness, and surveying currently available commercial material made by a number of different processes.
Date: January 2000
Creator: Horton, J. A. & Herchenroeder, J. W.
Partner: UNT Libraries Government Documents Department

Solidification process in melt spun Nd-Fe-B type magnets

Description: A generalized solidification model has been developed based on a systematic investigation on the microstructure of melt spun Nd-Fe-B alloys. Melt spinning was conducted on initial stoichiometric and TiC added Nd{sub 2}Fe{sub 14}B (2-14-1) compositions to produce under, optimally and over quenched microstructures. Microstructural characterization was carried out by TEM, SEM, Optical microscopy, XRD, DTA, VSM and DC SQUID techniques. By taking the dendritic breakup during recalescence into consideration, this generalized model has successfully explained the solidification process of the melt spun Nd-Fe-B alloys. Challenging the conventional homogeneous nucleation models, the new model explains the fine and uniform equiaxed 2-14-1 microstructure in optimally quenched ribbons as a result of the breakup of the 2-14-1 dendrites which nucleate heterogeneously from the wheel surface and grow dendritically across the ribbon thickness due to the recalescence. Besides this dendritic breakup feature, the under quenched microstructure is further featured with another growth front starting with the primary solidification of Fe phase near the free side, which results in a coarsely grained microstructure with Fe dendritic inclusions and overall variation in microstructure across the ribbon thickness. In addition, because a epitaxy exists between the Fe phase and the 2-14-1, the so-formed coarse 2-14-1 grains may be textured. C-axis texturing was observed in under quenched ribbons. As a constraint to solidification models in this system, the cause and characteristics of this phenomenon has been studied in detail to test the authors proposed model, and agreement has been found. An extension has also been made to understand the solidification process when TiC is added, which suggests that Ti and C slow down the growth front of both Fe and 2-14-1 phase.
Date: February 23, 1998
Creator: Li, C.
Partner: UNT Libraries Government Documents Department

Brittle fracture in Nd{sub 2}Fe{sub 14}B intermetallic magnets

Description: Efforts to understand and improve the fracture toughness of Nd{sub 2}Fe{sub 14}B permanent magnets require an understanding of the fracture process itself. Cleavage plane orientations in Nd{sub 2}Fe{sub 14}B were identified by X-ray diffraction and found to be rather random. Cleavage fracture surfaces often exhibited smooth curvatures with no evidence for cleavage steps. The small grain sizes of less than 100 nm in Magnequench MQ material preclude an easy assessment of the fracture mode by scanning electron microscopy. Auger electron spectroscopy showed that much of the surface is covered with a 1 nm thick layer of a neodymium-rich phase presumably the 70Nd-30Fe eutectic phase suggesting that the hard Nd{sub 2}Fe{sub 14}B grains do not cleave but instead failure is at or in the grain boundary phase.
Date: February 1998
Creator: Horton, J. A.; Heatherly, L.; Specht, E. D.; Li, D.; Herchenroeder, J. W. & Canfield, P. C.
Partner: UNT Libraries Government Documents Department

Microstructure and composition in rapidly-quenched NdFeB-based hard magnet alloys

Description: A detailed study of the microstructure and composition in hot-pressed (MQ-2) and die-upset (MQ-3) magnet alloys based on the Nd{sub 2}Fe{sub 14}B composition, utilizing high resolution and analytical transmission electron microscopy (TEM), is reported. The initial magnetic properties of the two samples show different behaviors, which are attributed to the difference in the anisotropy of the grain structure and the grain boundaries. The hot-pressed sample shows faceted grains of the 2-14-1 phase, while die-upset sample shows plate-like grains, together with larger equiaxed grains that contain a speckling of precipitates in the grain interior. The grain structure and composition remain rather similar in the two samples. The grain boundary phase averages approximately one nanometer to more than ten nanometers in width. The thicker grain boundaries are Nd-rich, while the thinner grain boundaries in the hot-pressed sample exhibit an Fe-rich composition near that of the NdFe{sub 3} phase. Nd-rich phases are found at the grain boundary junctions of both samples, with the Nd:Fe ratio near 7:3 in the die-upset sample, and up to 3:2 in the hot-pressed sample. The significance of the microstructure and the grain boundary phases on the magnetic behavior in the two samples is discussed.
Date: September 1, 1995
Creator: Nguyen, T.D.; Krishnan, K.M.; Lewis, L.H.; Zhu, Y. & Welch, D.O.
Partner: UNT Libraries Government Documents Department

A study of nitrogenation of a NdFe{sub 12-x}Mo{sub x} compound by in situ neutron powder diffraction.

Description: The effects on the crystal lattice of a NdFe{sub 12{minus}x}Mo{sub x}(x {approx_equal} 1.7) compound which contained {approximately}12 vol% of bcc-Fe were studied by neutron powder diffraction during controlled nitrogenation over the 25-600 C temperature range. The sample inside the furnace was connected to a closed volume of ultra-pure nitrogen gas while neutron data were collected over regular time intervals during sequential heating. Substantial nitrogen absorption occurred between 500 to 600 C. During the nitrogenation process the NdFe{sub 12{minus}x}Mo{sub x}N{sub y} lattice expanded while the bcc-Fe lattice contracted. An increasing decomposition of the compound into bcc-Fe at 600 C was observed. The average size of the NdFe{sub 12{minus}x}Mo{sub x}N{sub y} crystalline grains decreased starting at {approximately}300 C, reaching a minimum at {approximately}500 C and then increased markedly at higher temperatures. The development of lattice strains, on the other hand, showed an opposite trend, i.e., a maximum at 500 C. A correlation of structural modification of the crystalline phases and the nitrogenation process is discussed.
Date: November 18, 1997
Creator: Ding, Y.; Lin, J.; Loong, C.-K. & Short, S. M.
Partner: UNT Libraries Government Documents Department

Modification of cathodic arc deposition profiles by magnetic multicusps

Description: The deposition profile of a cathodic arc plasma source with and without magnetic macroparticle filter has been measured using a deposition probe technique. It has been found that the profile is close to a Gaussian and that the width of the profile depends on the cathode material. It was found that the dependence on the cathode material leads to a considerable radial variation of the elemental composition of the film when an alloy cathode is used. A magnetic multicusp field (magnetic bucket) near the exit of the plasma source or the magnetic filter was applied to flatten and homogenize the deposition profile.
Date: April 1, 1996
Creator: Anders, S.; MacGill, R. A.; Raoux, S. & Brown, I. G.
Partner: UNT Libraries Government Documents Department

Growth of oriented rare-earth-transition-metal thin films

Description: Rare-earth-transition-metal thin films are successfully grown by magnetron sputtering onto single-crystal MgO substrates with epitaxial W buffer layers. The use of epitaxial W buffer layers allows oriented single-phase films to be grown. Sm-Co films grown onto W(100), have strong in-plane anisotropy and coercivities exceeding 5 T at 5 K whereas Fe-Sm films have strong perpendicular anisotropy and are magnetically soft.
Date: April 1, 1996
Creator: Fullerton, E.E.; Sowers, C.H.; Bader, S.D. & Wu, X.Z.
Partner: UNT Libraries Government Documents Department

Magnetization reversal in melt-quenched NdFeB

Description: Melt-quenched NdFeB is an important modern permanent magnet material. However there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQIII compared with MQII and the increased dipolar interactions in MQIII.
Date: June 1, 1999
Creator: Crew, D.C.; Lewis, L.H.; McCormick, P.G.; Street, R. & Panchanathan, V.
Partner: UNT Libraries Government Documents Department

Factors affecting coercivity in rare-earth based advanced permanent magnet materials

Description: The relationships that link microstructural properties of advanced permanent magnet materials with magnetic properties such as the coercivity are often difficult to quantify, especially in materials with nano-scale structures. Recent work on RE{sub 2}Fe{sub 14}B-based powders fabricated with rapid-solidification techniques such as inert gas atomization (IGA) and melt-spinning provide insight into the nanostructural features which affect the acquisition and stability of coercivity. In all cases the coercivity is found to be a function of both the scale of the constituent microstructure and of the presence and distribution of minor phases.
Date: February 1, 1997
Creator: Lewis, L.H.; Sellers, C.H. & Panchanathan, V.
Partner: UNT Libraries Government Documents Department

Magnetic resonance force microscopy with a permanent magnet on the cantilever

Description: The magnetic resonance force microscope (MRFM) is a microscopic 3-D imaging instrument based on a recent proposal to detect magnetic resonance signals mechanically using a micro-mechanical resonator. MRFM has been successfully demonstrated in various magnetic resonance experiments including electron spin resonance, ferromagnetic resonances and nuclear magnetic resonance. In order to apply this ultra-high, 3-D spatial resolution technique to samples of arbitrary size and shape, the magnetic particle which generates the field gradient {del}{bold B}, (and, therefore, the force {bold F = (m {center_dot} {del}B)} between itself and the spin magnetization {bold m} of the sample) will need to be mounted on the mechanical resonator. Up to the present, all experiments have been performed with the sample mounted on the resonator. This is done, in part, to avoid the spurious response of the mechanical resonator which is generated by the variation of the magnetization of the magnetic particle as the external field is varied.
Date: February 1, 1997
Creator: Zhang, Z. & Hammel, P.C.
Partner: UNT Libraries Government Documents Department

Extrinsic Curie temperature and spin reorientation changes in Nd{sub 2}Fe{sub 14}B/{alpha}-Fe nanocomposites

Description: The Curie temperatures and spin reorientation temperatures of a series of four melt-spun nanocomposite materials comprised of Nd{sub 2}Fe{sub 1}4B and varying amounts of {alpha}-Fe were measured using independent techniques. The phase constitution and grain size was assessed with synchrotron x-ray diffraction; the Curie temperatures were measured by differential thermal analysis (DTA) and dc SQUID magnetometry in the temperature range 375 K {le} T {le} 800 K, whereas the spin reorientation transition temperature was determined from ac susceptibility measurements taken in the range 10 K {le} T {le} 300 K. The Curie temperature increases with increasing excess iron content, resulting in a 18 {degree} enhancement over the Curie temperature of pure Nd{sub 2}Fe{sub 14}B for 27 wt% excess {alpha}-Fe. The spin reorientation temperatures are depressed from the single-crystal value by an average of 10 degrees. Both anomalous effects are attributed to intergranular exchange coupling present in the alloys, although the effects of uncompensated stress between the constituent phases cannot be ruled out The experimental results suggest that while the Curie temperature of the Nd{sub 2}Fe{sub 14}B phase may be extrinsically enhanced significantly beyond the bulk value, possibly extending the range of applications of this compound, the anisotropy may be simultaneously lowered, impeding the attainment of high coercivities in these alloys.
Date: May 1, 1998
Creator: Lewis, L.H. & Panchanathan, V.
Partner: UNT Libraries Government Documents Department

Heat capacities, magnetic properties, and resistivities of ternary RPdBi alloys where R = La, Nd, Gd, Dy, Er, and Lu

Description: Over the past four and a half decades research on the rare earths, their compounds, and their alloys has yielded significant insights into the nature of materials. The rare earths can be used to systematically study a series of alloys or compounds. Magnetic ordering, crystalline fields, spin fluctuations, the magnetocaloric effect, and magnetostriction are a small sample of phenomena studied that are exhibited by the rare earth family. A significant portion of research has been conducted on the abundant RM{sub 2} and RM phases, where R is the rare earth and M is a transition metal. The natural progression of science has led to the study of related RMX ternary phases, where X is either another transition metal or semimetal. There are now over 1,000 known RMX phases. The focus of this study is on RPdBi where R = La, Nd, Gd, Dy, Er, and Lu. Their heat capacities, magnetic properties, and resistivities are studied.
Date: May 1, 1996
Creator: Riedemann, T.M.
Partner: UNT Libraries Government Documents Department

REC and NdFe magnetic moment irreversibility from temperature cycling

Description: Presented are the results of thermal cycling tests carried out on REC and NdFe samples, to determine the irreversible losses in room temperature open circuit magnetic moment. A stabilization prescription was developed for a REC alloy that will allow two 4 day/175/sup 0/C temperature cycles, which simulate two UHV bakeouts, with only a 0.35% average loss and a 0.65% loss variation in the room temperature open circuit magnetic moment after stabilization.
Date: October 1, 1985
Creator: Hoyer, E.; Chin, J.W.G. & Shuman, D.
Partner: UNT Libraries Government Documents Department

Site-dependent variation of spectroscopic relaxation parameters in Nd glasses

Description: Laser-induced fluorescence line-narrowing has revealed that the emission properties of Nd/sup 3 +/ in various glasses are strongly dependent on the nature of the site. In a mixed anion glass, the multiplicity of ligand combinations causes additional complications. The spectral and kinetic manifestations of these are presented and discussed.
Date: January 1, 1978
Creator: Brecher, C.; Riseberg, L.A. & Weber, M.J.
Partner: UNT Libraries Government Documents Department

QUARTERLY STATUS REPORT ON LAMPRE PROGRAM FOR PERIOD ENDING NOVEMBER 20, 1963

Description: The development and operation of the Los Alamos Molten Plutonium Reactor Experiments are described. The development and compatibility of iron-- plutonium and cerium-cobalt-- plutonium alloy fuels are evaluated. The fabrication and testing of the liquid sodiam loop are summarized. The phase studies of plutoniam alloys containing neodymium, scandium, yttrium, praseodymium, and cerium-- cobalt mixtures are reported. (N.W.R.)
Date: December 1, 1963
Partner: UNT Libraries Government Documents Department

A laboratory based system for Laue micro x-ray diffraction

Description: A laboratory diffraction system capable of illuminating individual grains in a polycrystalline matrix is described. Using a microfocus x-ray source equipped with a tungsten anode and prefigured monocapillary optic, a micro-x-ray diffraction system with a 10 mum beam was developed. The beam profile generated by the ellipsoidal capillary was determined using the"knife edge" approach. Measurement of the capillary performance, indicated a beam divergence of 14 mrad and a useable energy bandpass from 5.5 to 19 keV. Utilizing the polychromatic nature of the incident x-ray beam and application of the Laue indexing software package X-Ray Micro-Diffraction Analysis Software, the orientation and deviatoric strain of single grains in a polycrystalline material can be studied. To highlight the system potential the grain orientation and strain distribution of individual grains in a polycrystalline magnesium alloy (Mg 0.2 wt percent Nd) was mapped before and after tensile loading. A basal (0002) orientation was identified in the as-rolled annealed alloy; after tensile loading some grains were observed to undergo an orientation change of 30 degrees with respect to (0002). The applied uniaxial load was measured as an increase in the deviatoric tensile strain parallel to the load axis (37 References).
Date: February 28, 2007
Creator: Source, Advanced Light; Tamura, Nobumichi; Lynch, P.A.; Stevenson, A.W.; Liang, D.; Parry, D. et al.
Partner: UNT Libraries Government Documents Department

The Beam Line X NdFe-steel hybrid wiggler for SSRL

Description: A wiggler magnet with 15 periods, each 12.85 cm long, which achieves 1.40 T at a 2.1 cm gap (2.26T at 0.8 cm) has been designed and is now in fabrication at LBL. This wiggler will be the radiation source of the high intensity synchrotron radiation beam line for the Beam Line X PRT facility at SSRL. The magnet utilizes Neodymium-Iron (NdFe) material and Vanadium Permendur (steel) in the hybrid configuration to achieve simultaneously a high magnetic field and short period. Magnetic field adjustment is with a driven chain and ball screw drive system. The magnetic structure is external to an s.s. vacuum chamber which has thin walls, 0.76 mm thickness, at each pole tip for higher field operation. Magnetic design, construction details and magnetic measurements are presented.
Date: March 10, 1987
Creator: Hoyer, E.; Halbach, K.; Humphries, D.; Marks, S.; Plate, D.; Shuman, D. et al.
Partner: UNT Libraries Government Documents Department

CSEM-steel hybrid wiggler/undulator magnetic field studies

Description: Current design of permanent magnet wiggler/undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (H/sub c/ = 9.2 kOe) and NdFe (H/sub c/ = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields.
Date: May 1, 1985
Creator: Halbach, K.; Hoyer, E.; Marks, S.; Plate, D. & Shuman, D.
Partner: UNT Libraries Government Documents Department

Magnetic and electronic properties of Nd--La and Ce--La alloys

Description: The electrical resistivity, thermoelectric power and magnetic susceptibility on Nd single crystals and polycrystalline dhcp Nd--La and Ce--La alloys have been measured at low temperatures. The measurements on the Nd--La alloys show features at the Neel temperatures and also show additional magnetic ordering phenomena. Some of these other features are dependent on the thermal history of the sample. Magnetic field studies are needed to correlate these features with observed neutron diffraction effects. Several magnetic features are seen in the Ce--La alloy system also, although the measurements are plagued with the problem of fcc contamination. In addition, alloys containing Ce show Kondo effects. The logarithmic term in the resistivity is explained well by the theory of Liu et al. which uses a mean field to approximate the 4f-4f interactions in the nondilute alloys. The large peak in the thermopower of Ce--La alloys is explained well by the theory of Bhattacharjee and Coqblin which incorporates Kondo scattering from excited crystal field levels.
Date: May 1, 1979
Creator: Petersen, T.S.
Partner: UNT Libraries Government Documents Department