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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Developing highly coercive microstructures in Pr–Co magnets by Gd substitution

B. E. Meacham and D. J. Branagan

J. Appl. Phys. 93, 7963 (2003); http://dx.doi.org/10.1063/1.1541656 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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While permanent magnets based on Sm1Co5 are technologically important, magnets made from isostructural Pr1Co5 are not commercially significant even though Pr1Co5 has better intrinsic magnetic properties. The biggest problem is the formation of unfavorable phase equilibria which leads to an inability to develop high coercivity in binary Pr–Co alloys. A proposed solution was to make a hyperstoichiometric alloy with Gd as a substitute, in addition to carbon, to inhibit the formation of the deleterious phases leading to a predominantly single magnetic phase composition. An enhancement was observed in the coercivity. This result is perhaps surprising considering that the Gd atom, with a spherical 4f electron shell, is not expected to contribute to the magnetocrystalline anisotropy. Thus, the expectation was that the coercivity increase was caused by the microstructure but no distinguishing feature of microstructure was observed in transmission electron microscopy. It appears that Gd substitution instead affects the intrinsic magnetocrystalline anisotropy by reducing the effect of the small canting of the Pr moment through dilution. © 2003 American Institute of Physics.
Show PACS
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
68.37.Lp Transmission electron microscopy (TEM)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Effects of grain size and morphology on the coercivity of Sm2(Co1−xFex)17 based powders and spin cast ribbons

Christina H. Chen, Steve Kodat, Michael H. Walmer, Shu-Fan Cheng, Matthew A. Willard, and Vincent G. Harris

J. Appl. Phys. 93, 7966 (2003); http://dx.doi.org/10.1063/1.1558272 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2003

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The effects of grain/particle size and morphology on the coercivity of Sm2(Co1−xFex)17 based powders and spin cast ribbons are investigated in an attempt to make pure Sm–Co 2:17 magnets with a higher energy product than that currently available. It is observed that the coercive force is not only affected by the composition, but also significantly by the grain/particle size. The coercivity of the as-cast SmCo6 powder was increased from 0.5 to ∼12 kOe when the grain/particle size was decreased from 14 to 1.5 μm. A twofold increase in coercivity was also observed for some Sm(CO0.85Fe0.15)7.6 spin cast ribbons when the wheel speed was increased from 6 to 25 m/s and the grain size of the ribbons was decreased from 2–15 to 0.5–5 μm. The initial magnetization curves show a high degree of texture that exists in the free side of ribbons, with the c axis parallel to the longitudinal direction of the ribbons. The presence of a trace of boron in the ribbons changes the grain morphology and eliminates the texture. Some results show promise of making a high coercivity higher energy product Sm2(Co1−xFex)17 based magnets without adding nonmagnetic elements such as Cu and Zr. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

High hysteresis in a homogeneous metallic glass

D. J. Branagan, B. E. Meacham, R. W. McCallum, K. W. Dennis, and M. J. Kramer

J. Appl. Phys. 93, 7969 (2003); http://dx.doi.org/10.1063/1.1538178 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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In this article, we demonstrate high hysteresis in a well characterized homogeneous Tb–Al glass which contained no crystallites or crystalline embryos as verified using conventional and synchrotron diffraction, neutron diffraction, and direct observation in the transmission electron microscope. At low temperature (2 K), the metallic glass structure exhibited intrinsic coercivities approaching 23 kOe and high isotropic energy products of 12.4 MGOe. After crystallization into a three-phase nanoscale structure, the hard magnetic properties were found to be far inferior to that obtainable in the glass structure. From the well defined intrinsic magnetic properties (Msat,Tc), it is clear that the glass contains one or more types of well defined associations (i.e., clusters) and that these associations lead to ferromagnetic coupling/ordering. From the large random magnetic anisotropy, it is probable that the domain size is much larger than the structural cluster size. The measured single-phase loop shapes and the development of high coercivity in the glass state can be explained by an “exchange bias” mechanism resulting in a near perfect distribution of “fragile” pinning centers. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Et Exchange and superexchange interactions
61.43.Fs Glasses
75.50.Cc Other ferromagnetic metals and alloys

Structure and magnetic properties of Sm(Co1−xZrx)y alloys (x=0.03–0.05,y=12–15) and melt-spun Sm(Co,Fe,Zr,Cu,Ga,B)12 material

M. Q. Huang, Z. Turqut, S. Y. Chu, J. C. Horwath, R. T. Fingers, B. R. Smith, Z. M. Chen, and B. M. Ma

J. Appl. Phys. 93, 7972 (2003); http://dx.doi.org/10.1063/1.1541645 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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Alloys with nominal compositions of Sm(Co1−xZrx)y (x=0.03–0.05, y=12–15) were synthesized by arc melting and characterized in the temperature range of 10–1473 K and with a magnetic field up to 5 T. Near-single-phase materials with Th2Ni17 structure were formed in the as-cast alloys with x=0.05. Similar to Ti, Zr also stabilizes the Th2Ni17 structure. Hard magnetic properties with Tc∼1142–1179 K, Ms∼110–123 emu/g, and Ha∼63–86 kOe at 300 K have been observed. An alloy with a nominal composition of Sm(Co0.75Fe0.1Zr0.05Cu0.08Ga0.01B0.01)12 was also prepared by melt spinning. The melt spun materials were nanostructured in nature and magnetically hard in the as-spun states. Hci∼10 kOe, Bs∼9.5 kG, and Hci∼27 kOe, Bs∼9.8 kG were obtained at 300 and 10 K, respectively. The effects of the heat treatment conditions on magnetic properties of both alloys and ribbon will be also discussed. © 2003 American Institute of Physics.
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75.50.Vv High coercivity materials
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
61.66.Dk Alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Microstructure, microchemistry, and magnetic properties of melt-spun Sm(Co,Fe,Cu,Zr)z magnets

A. Yan, O. Gutfleisch, A. Handstein, T. Gemming, and K.-H. Müller

J. Appl. Phys. 93, 7975 (2003); http://dx.doi.org/10.1063/1.1537700 (3 pages) | Cited 17 times

Online Publication Date: 9 May 2003

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The evolution of the microstructure, microchemistry, and magnetic properties during slow cooling of melt-spun Sm(Co,Fe,Cu,Zr)z magnets was investigated. It was found that uniform cellular and lamellar structures are formed upon isothermal aging the as-spun ribbons at 850 °C for 3 h, without subsequent slow cooling. No microstructural changes and no obvious difference in the Cu content in the 2:17 matrix phase were observed after slow cooling but the coercivity was significantly enhanced from 0.32 to 3 T. A large gradient of the Cu content in the cell boundary phase was detected in the highly coercive melt-spun Sm(Co,Fe,Cu,Zr)z ribbons with slow cooling by nanoprobe chemical analysis, in contrast to a homogeneous Cu distribution in the cell boundary phase of the ribbons without slow cooling. Further investigation revealed that a spinodal structure is developed in the Cu-rich Sm(Co,Cu)5 cell boundary phase of 2:17 SmCo magnets during slow cooling and the high coercivity of the 2:17 type magnets could result from the large gradient of domain wall energy within the cell boundary phase. © 2003 American Institute of Physics.
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81.40.Rs Electrical and magnetic properties related to treatment conditions
81.05.Bx Metals, semimetals, and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
75.60.Ch Domain walls and domain structure

Effect of Co substitution on the crystallization behavior and magnetic properties of melt-spun (Pr,Tb)2(Fe,Nb,Zr)14B/α-Fe nanocomposites

H. Wang, Y. Zhang, Z. Q. Jin, and G. C. Hadjipanayis

J. Appl. Phys. 93, 7978 (2003); http://dx.doi.org/10.1063/1.1558273 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The influence of Co substitution on the crystallization behavior and magnetic properties of (Pr,Tb)2(Fe,Nb,Zr)14B/α-Fe nanocomposites was investigated in melt-spun Pr7Tb1Fe87Nb0.5Zr0.5B4 and Pr7Tb1Fe57Co30Nb0.5Zr0.5B4 samples. Crystallographic textures were observed for all constituent phases in both sample S spun at wheel speeds less than 15 m/s. Both alloys show a fully amorphous structure when spun at a speed faster than 40 m/s which crystallizes into the TbCu7 structure before it finally transforms into the 2:14:1 phase. The Curie temperature of α-Fe and Pr2Fe14B phase increases greatly with the substitution of 30% Co for Fe. However, both the coercivity and energy product decrease. Optimum magnetic properties are found in the Pr7Tb1Fe87Nb0.5Zr0.5B4 sample with coercivity Hc=6.84 kOe and (BH)max=11.8 MG Oe. © 2003 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.50.Bb Fe and its alloys
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetism of Ir in Fe2IrSi from Ir L2,3 edge x-ray magnetic circular dichroism spectroscopy

V. V. Krishnamurthy, J. L. Weston, G. J. Mankey, M. Suzuki, N. Kawamura, and T. Ishikawa

J. Appl. Phys. 93, 7981 (2003); http://dx.doi.org/10.1063/1.1558274 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The formation of an induced 5d magnetic moment on Ir in a new ferromagnetic compound Fe2IrSi [Curie temperature 662(15) K], which forms in the L21 structure, has been investigated by x-ray magnetic circular dichroism and x-ray absorption spectra measurements at Ir L2,3 edges at 297 K. Using the sum rules which relate the integrals of these spectra with the expectation ground state value of the orbital angular momentum 〈LZ〉 of the probe atom, the orbital moment of Ir could be determined as 0.0036(2)μB. The orbital moment to spin moment ratio is found to be 0.0240(15). Assuming ferromagnetic coupling between Ir and Fe and that the total magnetic moment of Fe2IrSi follows Slater–Pauling behavior, we estimate the magnetic moment of Fe at 0 K as 1.4μB/atom. © 2003 American Institute of Physics.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Bb Fe and its alloys
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Magnetic domain structure of Fe–55 at. %Pd alloy at different stages of atomic ordering

Lisha Wang, David E. Laughlin, Y. Wang, and Armen G. Khachaturyan

J. Appl. Phys. 93, 7984 (2003); http://dx.doi.org/10.1063/1.1541646 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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In this work, we use Lorentz microscopy imaging technique to study the magnetic domain structure of Fe–55 at %Pd alloy at different stages of atomic ordering. The underlying microstructure is characterized by using conventional transmission electron microscopy. At low annealing temperature, a tweed microstructure is formed. The ordered c variants in the tweed microstructure align along {110} plane traces. At higher annealing temperatures, a polytwinned structure is formed. The increase in the coercivity of the tweed structure is related to the density of magnetic macrodomain intersection with the tetragonal variants. After long time annealing, coarsened L10 grains are formed. Two types of magnetic domains are found in these coarsened grains. One is the “stripe” magnetic domain where the magnetization direction or the c axis of the L10 grain is perpendicular to the surface orientation. The other is “plate-like” magnetic domain; the magnetization direction of the L10 grain is found to be parallel to the specimen surface orientation. © 2003 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
61.66.Dk Alloys
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Plasma sprayed Nd–Fe–B permanent magnets

M. Willson, S. Bauser, S. Liu, and M. Huang

J. Appl. Phys. 93, 7987 (2003); http://dx.doi.org/10.1063/1.1558590 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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This study demonstrated that the plasma spray deposition method is an alternative process for producing Nd–Fe–B magnets in addition to the two existing principal processes: the powder metallurgy process for producing sintered Nd–Fe–B magnets and the melt spinning process for bonded Nd–Fe–B magnets. Plasma spray is a potentially better process for producing magnetic parts with complicated shape, large area, thin thickness, small dimension, or unusual geometry. High intrinsic coercivity greater than 15 kOe was readily obtained for Nd16Dy1Fe76B7 even in the as-deposited condition when the substrate was preheated. The plasma spray process contains only three steps: melting, crushing, and plasma spray, which is much simpler than the powder metallurgy and melt spinning processes. Without preheating the substrate, the coercivity was usually very low (∼0.1 kOe) in the as-deposited condition and it increased to 10 to >15 kOe after anneal. Evidence of magnetocrystalline anisotropy was observed in plasma sprayed Nd15Dy1Fe77B7 magnets when the substrate was not preheated. It is believed that a crystal texture was developed during the plasma spray as a result of the existence of a temperature gradient in the solidifying melt. © 2003 American Institute of Physics.
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75.50.Ww Permanent magnets
81.05.Bx Metals, semimetals, and alloys
81.15.Rs Spray coating techniques
75.50.Bb Fe and its alloys
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Rs Electrical and magnetic properties related to treatment conditions

Role of the Fe sublattice on the Invar anomaly in R2Fe14B compounds

Ning Yang, K. W. Dennis, R. W. McCallum, M. J. Kramer, Yuegang Zhang, and Peter L. Lee

J. Appl. Phys. 93, 7990 (2003); http://dx.doi.org/10.1063/1.1541647 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Thermal expansion anomalies of Nd2Fe14B and Y2Fe14B stoichiometric compounds have been studied by x-ray diffraction with high energy synchrotron radiation using a Debye–Scherrer geometry from room temperature to 1000 K. Y2Fe14B and Nd2Fe14B have similar temperature dependence of lattice parameters and bond distances up to their Curie temperatures Tc. The volumetric spontaneous magnetostriction at room temperature for Nd2Fe14B and Y2Fe14B were determined to be 1.49% and 1.45%, respectively. Among the Fe–Fe bonds, those bonds containing Fe(j2), whose projections are dominantly in the basal plane, have the highest contribution to the Invar effect. These bonds have magnetostrictive strain ranging from 0.4% to 0.8% at room temperature. Above the Curie temperature, Y2Fe14B has an isotropic thermal expansion, while Nd2Fe14B exhibits slightly anisotropic thermal expansion. The iron sublattices dominate the spontaneous volumetric magnetostriction of Y2Fe14B and Nd2Fe14B compounds. © 2003 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
65.40.De Thermal expansion; thermomechanical effects
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Processing induced changes in Curie temperature of Nd2Fe14B melt-spun ribbons

Youwen Xu, Ning Yang, K. W. Dennis, R. W. McCallum, M. J. Kramer, Yuegang Zhang, and Peter L. Lee

J. Appl. Phys. 93, 7993 (2003); http://dx.doi.org/10.1063/1.1541648 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Changes of the Curie temperature Tc in Nd2Fe14B (2-14-1) can arise from changes in crystal chemistry or can be induced by compressive stresses. We have recently observed decreases in the Tc up to 30 K in nanocomposite melt-spun ribbons of 2-14-1 and α-Fe. The starting materials contain about 6.5%–15% additional Fe, while some samples had 3 wt % Ti–C added to control grain growth. Spin reorientation temperatures Ts measured on the samples with or without Ti–C are from 120 to 122 K depending on the wheel speed and composition, suggesting that changes in Tc are due to microstructure. X-ray diffraction dilatometry using the α-Fe lattice suggests that at 300 K the iron is under tension but switches sign due to differences in coefficients of thermal expansion between the α-Fe and 2-14-1. Similar d spacing of the (110) of α-Fe and (006) of 2-14-1 suggest that changes in Tc may in part be due to epitaxial stresses affecting the exchange coupling in the nanocomposite alloys. © 2003 American Institute of Physics.
Show PACS
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
61.46.-w Structure of nanoscale materials
75.80.+q Magnetomechanical effects, magnetostriction
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.30.Et Exchange and superexchange interactions
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