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  • 1
    Electronic Resource
    Electronic Resource
    Coercivity in mechanically milled Pr–Co–Zr powders with TbCu7 structure (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5302-5304 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural, microstructural, and magnetic properties of the PrCo7−xZrx (x=0, 0.2, 0.3, and 0.4) powders produced by mechanical milling have been studied with the aim of developing fine microstructure and high coercivity in these powders. X-ray diffraction, transmission electron microscope, and magnetic measurements show that a single phase with TbCu7-type structure and with high anisotropy of up to 100 kOe is obtained in as-cast PrCo6.7Zr0.3 alloy. Magnetic hardening is developed in the mechanically milled powders. An optimum coercivity of 5.3 kOe has been obtained in PrCo6.7Zr0.3 powders milled for 2 h and annealed at 800 °C for 1 min, which shows a uniform microstructure of the 1:7 phase with an average grain size of about 10–15 nm. The observed magnetic hardening is believed to arise from the high anisotropy field of the Pr(Co, Zr)7 phase and the uniform nanoscale microstructure developed by mechanical milling and subsequent annealing. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373328
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructure and magnetic properties of mechanically milled nanograined PrxCo100−x (x=15.4−20.5) powders (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1547-1551 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure, microstructure, and magnetic properties of high-coercivity PrCo5-based PrxCo100−x (x=15.4–20.5) powders synthesized by mechanical milling and subsequent annealing were systematically studied as a function of Pr content. While the magnetization decreases monotonously with the Pr content, the coercivity increases, reaching a maximum of 24.1 kOe in Pr19Co81, and then decreases for higher Pr content. As a result, the maximum energy product goes through a broad peak of about 11.3–11.8 MGOe at the 16.7–18.0 at. % Pr content. Microstructural studies reveal that a uniform nanoscale PrCo5/Pr2Co17 microstructure with an average grain size of about 15–30 nm is developed in powders with Pr content up to 19 at. %. The volume fraction of the Pr2Co17 decreases with Pr content and a nearly single PrCo5 structure is obtained in Pr19Co81 powders. Further increase in the Pr content leads to the presence of the less-hard Pr2Co7 phase in the form of large grains, resulting in lower coercivities. Evidence of intergranular exchange coupling is found in all the samples. The results suggest that the observed magnetic hardening originates from the high anisotropy field of the PrCo5 phase and the uniform nanoscale microstructure developed by the processing used. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373853
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  • 3
    Electronic Resource
    Electronic Resource
    Enhancement of Curie temperature of the 2:17 phase in nanocomposite Sm2(Fe,Co)15Cr2C2/(Fe,Co) magnets (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3857-3862 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The proximity effect on the Curie temperature of exchange-coupled melt-spun nanocomposite Sm2(Fe,Co)15Cr2C2/(Fe,Co) magnets consisting of a fine mixture of hard and soft phases has been examined using thermomagnetic measurements, x-ray diffraction (XRD), Mössbauer and transmission electron microscopic studies. A significant enhancement in the Curie temperature of the 2:17 phase is observed in these magnets (27 °C in Sm2Fe15Cr2C2 and 102 °C in Sm2Fe11Co4Cr2C2) as compared to their patent cast alloys. XRD and Mössbauer analysis confirm that both the cast alloys and the nanocomposite magnets are comprised of the same phases [rhombohedral 2:17 and bcc Fe(Co)]. The unit cell volume of the 2:17 phase is slightly larger in ribbons and it is found to contribute to about 15% of the total Curie temperature enhancement. Microstructural studies revealed that the grain size is reduced from 10 to 20 μm in the cast alloy to 20–60 nm in the melt-spun magnets. The enhancement of the Curie temperature is believed to arise mainly from the exchange coupling effect between the 2:17 phase and the Fe(Co) phase which results in an extra exchange field at the 2:17 grains. Furthermore, the enhancement of the Curie temperature is found to increase with the volume fraction of the Fe(Co) phase in the magnets. It is also interesting to note that the Curie temperature of the Fe(Co) phase in the magnets remains unchanged as compared with their parent alloys, because the exchange coupling effect disappears completely at temperature above the Curie temperature of the 2:17 phase. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371299
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic properties and microstructure of mechanically milled Sm2(Co,M)17-based powders with M=Zr, Hf, Nb, V, Ti, Cr, Cu and Fe (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3409-3414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure, microstructure, and magnetic properties of nanostructured Sm2Co17-based powders synthesized by mechanically milling and subsequent annealing have been systematically studied. It has been found that a nanoscale 2:17 phase with an average grain size of about 30 nm is developed within the powders, which have an average particle size of about 5 μm. Optimum magnetic properties of Ms=110.5 emu/g, Mr=66.2 emu/g, Mr/Ms=0.60, Hc=9.6 kOe, and (BH)m=10.8 MGOe have been obtained in stoichiometric Sm2Co17 powders milled for 6 h and annealed at 800 °C for 30 min. The observed magnetic hardening is believed to arise from the high anisotropy of the Sm2Co17 phase and its nanoscale grain size. A small amount of Zr substitution for Co significantly increases the coercivity by increasing the anisotropy field of the Sm2Co17 phase. Cu substitution in Zr-contained samples further increases the coercivity by introducing a nanoscale 1:5 phase which forms a uniform mixture with the 2:17 nanograins. The highest coercivity of 20.6 kOe has been obtained in the Sm12(Co0.92Cu0.06Zr0.02)88 powders. Fe substitution enters the Co lattice sites of the 2:17 structure, leading to an increase of the magnetization but a decrease of the coercivity. An optimum maximum energy product of 14.0 MGOe is obtained in the Sm12(Co0.7Fe0.3)88 powders. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372359
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  • 5
    Electronic Resource
    Electronic Resource
    Enhancement of magnetic properties of nanocomposite Pr2Fe14B/α-Fe magnets by small substitution of Dy for Pr (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2299-2303 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocomposite (Pr,Dy)2Fe14B/α-Fe magnets with compositions Pr8−xDyxFe86B6 (x=0, 0.5, 1, 1.5, and 2) have been synthesized by melt spinning using low wheel speeds in the range from 18 to 21.7 m/s. It has been found that the coercivity is significantly increased by Dy substitution. An optimum coercivity of 6.6 kOe is obtained in the Pr7Dy1Fe86B6 magnet as compared to 4.3 kOe in the Pr8Fe86B6 magnet. As a result, the energy product is increased from 9.1 MGOe in the Pr8Fe86B6 magnet to 16.9 MGOe in the Pr7Dy1Fe86B6 magnet. The reason for this is the finer and more uniform 2:14:1/α-Fe nanoscale microstructure developed in the magnets with Dy substitution. Because of the low wheel speed spinning, the majority of the nanoscale microstructure is crystallized directly out of the melt. The enhancement of magnetic properties by Dy substitution is mainly due to the microstructure refinement which leads to an enhanced exchange coupling between the Pr2Fe14B and α-Fe, whereas the anisotropy increase by the Dy substitution provides only a minor contribution to the enhanced coercivity. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1344221
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructure and magnetic properties developed by hot pressing of cast Pr–Fe–B magnets (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2799-2804 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hot pressing process of cast Pr19Fe74.5B5Cu1.5 magnets were studied. Microstructure studies reveal that during the hot pressing, the crushing of Pr2Fe14B matrix grains and the relative slip and rotation between the grains take place and the Pr-rich melt is squeezed out of the magnet, leading to fine, dense and well-aligned Pr2Fe14B grains surrounded by a thin Pr-rich phase layer in the fully-deformed magnets. Magnetic properties of Br=9.9 kG, iHc=11.0 kOe and (BH)max=24.0 MG Oe are obtained. The increase of coercivity is attributed to the fine Pr2Fe14B grains and the thin Pr-rich phase layer continuously distributed at the grain boundaries. The increasing remanence results primarily from the development of the easy-axis alignment as well as from the densification of the Pr2Fe14B matrix. The easy-axis alignment is developed by the relative slip and rotation of the crushed Pr2Fe14B grains. A full and slow hot pressing is necessary for developing a good easy-axis alignment and high magnetic properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351030
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  • 7
    Electronic Resource
    Electronic Resource
    A new stable ferromagnetic phase in Nd-Fe-B magnets and its effect on coercivity (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 3596-3598 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and coercivity of NdxFe93−xB7 (x=16–28) sintered magnets were systematically studied. A new stable ferromagnetic phase with a composition of NdFe2Ox (x≈0.3) and a Curie temperature of 145 °C is found in the intergranular regions of the magnets, owing to the introduction of oxygen in the magnet processing. It forms at ∼650 °C and its volume fraction reaches a maximum of ∼4% in the Nd22Fe71B7 magnets. The coercivity is considerably enhanced by the appearance of this new phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354494
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  • 8
    Electronic Resource
    Electronic Resource
    Improvement of magnetic properties and intergranular microstructure of Nd–Fe–B magnets by intergranular addition of MgO oxide : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4456-4458 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work we have studied in detail the effect of MgO on magnetic properties and intergranular microstructure. We have found that both coercivity and thermal stability can be remarkably enhanced by the intergranular addition of MgO. For Nd22Fe71B7 magnets with 2 wt % MgO addition, the coercivity at room temperature and 180 °C are enhanced from 17.0 and 3.2 kOe to 22.1 and 5.2 kOe, respectively, and the reversible and irreversible flux loss from room temperature to 180 °C is reduced from 25.4% and 5.2% to 20.5% and 0.5%, respectively. Microstructural studies reveal that a new intergranular Nd–O–Fe–Mg phase with a composition close to Nd70O23Fe3Mg2 appears in the magnets with MgO addition. The improvement of magnetic properties by the MgO addition is believed to be due to the appearance of a Nd–O–Fe–Mg intergranular phase, which probably hinders the propagation of the domain walls between Nd2Fe14B grains. It is further found that the addition of Mg or O alone into the intergranular regions of the magnets does not lead to the formation of this Nd–O–Fe–Mg intergranular phase, and thus, cannot substantially improve the coercivity and the thermal stability of the magnets. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364974
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of grain size, Cu addition, and Nd substitution for Pr on intrinsic coercivity in cast–hot-pressed Pr-Fe-B magnets (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2868-2870 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coercivity of anisotropic cast–hot-pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation-controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse-grained cast structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349351
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic properties and microstructure of nanocomposite R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd, Pr) magnets (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5908-5910 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocomposite R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd, Pr) magnets prepared by crystallizing the as-made R8(Fe,Co,Nb)86B6 amorphous melt-spun ribbons have been studied. The coercivity is found to depend mainly on the grain size of the soft phase which is very sensitive to the sample composition. The average grain size is about 30 nm in R8Fe86B6, but the microstructure is not homogeneous and there are several large α-Fe grains with sizes up to 50–100 nm. The coercivities are 3.3 kOe in Nd8Fe86B6 and 4.9 kOe in Pr8Fe86B6 samples. Nb substitution significantly reduces the grain size of α-Fe and increases the coercivity. The highest coercivities obtained are 5.5 kOe in Nd8(Fe0.97Nb0.03)86B6 and 9.3 kOe in Pr8(Fe0.92Nb0.08)86B6 samples. Co substitution for Fe increases the grain size of both the 2:14:1 phase and α-Fe and dramatically decreases the coercivity. Increasing the B content in Co substituted samples leads to the formation of a more homogeneous and finer microstructure and thus to a partial recovery of the coercivity from 2.3 kOe in Nd8((Fe0.5Co0.5)0.97Nb0.03)86B6 to 4.3 kOe in Nd8((Fe0.5Co0.5)0.97Nb0.03)82B10 and from 2.1 kOe in Pr8((Fe0.5Co0.5)0.94Nb0.06)86B6 to 6.5 kOe in Pr8((Fe0.5Co0.5)0.94Nb0.06)82B10. It is further found that Co substitution improves the temperature dependence of the saturation magnetization. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369910
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