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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-reorientation transitions in (Pr1−xRx)Co5+δ, where R=Sm, Gd, Tb, Dy, Ho, and Er were determined by ac susceptibility measurements. The spin-reorientation temperature TSR of PrCo5 decreases from 105 K to lower temperatures when Pr is partially replaced by Sm, Gd, or Er. This decrease arises from different causes: the decrease of TSR in (Pr1−xGdx)Co5 results from the dilution of nonaxial anisotropy on the Pr sublattice, while the decrease of TSR in (Pr1−xSmx)Co5 and (Pr1−xErx)Co5+δ is due to the positive second-order Stevens coefficients of Sm and Er which yield uniaxial anisotropies. Rare earths of negative second-order Stevens coefficients such as R=Tb and Dy give rise to axial to conical and conical to planar transitions for x(approximately-greater-than)0.3 and 0.4 in (Pr1−xTbx)Co5+0.1x and (Pr1−xDyx)Co5+0.2x, respectively. Magnetic anisotropy phase diagrams of these systems are constructed accordingly.〈UFMMM〉
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6471-6473 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microstructures of cast Nd15Fe78B7 ingots with thicknesses of 8.7 and 4.4 mm have been investigated. Usually, a flat cast ingot consists of three different types of grains: fine, coarse, and columnar grains. Fine grains appear near the cast interface, columnar grains usually show in regions which undergo directional solidification and coarse grains exist in regions of a lower solidification rate. Low solidification rate results in a segregation of dendritic Fe, which is undesirable in magnet processing. Magnets made from a 8.7-mm-thick ingot yield a Br of 11.7 kG and a BHmax of 34.0 MGOe while magnets made from a 4.4 mm ingot give rise to a Br of 12.3 kG and a BHmax of 37.5 MGOe. The magnetic properties of final magnets have been correlated to the microstructures in flat cast ingots. Columnar grains have been shown to be desirable for achieving higher Br and BHmax in final magnets.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6027-6029 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A number of metal-bonded Sm2Fe17-N magnets have been fabricated. These magnets exhibit iHc = 5.1–17.0 kOe, Br = 6.4–8.4 kG, (BH)max=5.0–10.8 MGOe, Tc = 757 K, and ρ=6.2–6.7 g/cm3. Powder metallurgical techniques have been employed with a mixture of powdered Sm2Fe17-N and Zn, Sn, or In. Heat treatment is carried out in the temperature range of 160–450 °C in a N2 atmosphere at pressures ranging from 0–900 psi. The effects of Zn, Sn, and In contents and heat treatment conditions on the magnetic properties have been studied. Zn as the binder significantly enhances the coercivity iHc from 1.8–2.5 kOe for Zn-free magnets to 5–17 kOe for 9–20-wt. % Zn-containing magnets. The Fe-Zn phase, FeZn4, and/or Fe3Zn7, formed during heat treatment, may play an important role in producing a high coercivity. Sn-bonded magnets exhibit significant coercivity, whereas the In-bonded materials do not. The coercivity behavior is discussed in terms of the chemistry of the system.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6131-6133 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-reorientation phenomenon in the PrCo5 compound has been analyzed over the temperature range 0 to 300 K using a Hamiltonian consisting of the crystal-field term and the 4f–3d exchange interaction. We have performed a careful analysis by including the second- and the fourth-order interaction terms to the crystal-field Hamiltonian. In general, the crystal-field B02 term favors the planar anisotropy while B04 term promotes an axial anisotropy. The combination of these two terms yield the off-axial anisotropy of the Pr sublattice. The magnitudes of B02 and B04 contribution are relatively strong at low temperatures and decrease considerably with increasing temperature. The contribution of the B02 term is more pronounced than that of the B04 term throughout the temperature range investigated. The competition between the off-axial anisotropy of Pr sublattice and the axial anisotropy of Co sublattice yields the spin-reorientation transition phenomenon in PrCo5 at 105 K.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4610-4612 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd15.4Fe77.8B6.8 magnets of various degrees of crystal alignment have been prepared by the conventional powder metallurgy technique. The alignment of these magnets have been determined by x-ray diffraction and fitting the standard deviation of a Gaussian distribution for the relative intensity versus the angle between the normals of (hkl) and the tetragonal c axis. The standard deviation is a good indicator for crystal alignment. An aligning field of 8 kOe is found to be essential to obtain a well-aligned NdFeB magnet. The remanence of sintered magnets is directly affected by the crystal alignment. Furthermore, the effect of crystal alignment on the remanence follows the theoretical prediction of the Stoner–Wohlfarth model. Below the spin reorientation temperature, the effect of crystal alignment on the shape of hysteresis loop becomes more significant. The remanences extrapolated from first and second quadrant of the hysteresis loops have been found to be consistent with the prediction of Stoner–Wohlfarth model.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4981-4983 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd2Co7−xFexB3 alloys have been synthesized and studied at temperatures from 4 to 1100 K at fields up to 90 kOe. The structure and magnetic properties vary significantly with changing Fe content. The main phase is observed to be of hexagonal symmetry for x〈3. For x〉4 it is multiphase, the major phase having tetragonal symmetry. The Tc increases from 330 to 885 K when x varies from 0 to 3, then decreases from 885 to 577 K when x increases from 3 to 7. The saturation magnetization is 8μB/fu at 4.2 K, for Nd2Co7B3; it increases with increasing Fe content. The alloys exhibit a conical (0〈x〈3) and an axial (x〉4) magnetocrystalline anisotropy at 295 K. They all exhibit conical magnetic anisotropy at 77 K.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6119-6121 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin-reorientation phenomena in (TbxEr1−x)TiFe11 systems have been studied over the temperature range from 20 to 1000 K using susceptibility measurement. In this alloy series, the lattice constants, both a and c, increase with increasing x, as expected from the lanthanide contraction. For x〈0.5, the (TbxEr1−x)TiFe11 systems were found to exhibit axial-to-conical spin-reorientation transitions with a Tsr decrease with increasing x. However, for x(approximately-greater-than)0.5, the spin-reorientation transitions have been found to be axial-to-planar, on cooling, and the Tsr increases with increasing x. The magnetic phase diagram of (TbxEr1−x)TiFe11 has been constructed.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pr2Co7−xFexB3(0≤x≤7) alloys have been synthesized and studied at temperatures from 4 to 1100 K at fields up to 90 kOe. The structure and magnetic properties vary significantly with increasing Fe content. The material exhibits the Ce2Co7B3 structure for 0≤x≤0.5. For 0.5≤x≤3 the alloy is comprised of a main phase of hexagonal structure. A change in magnetocrystalline anisotropy occurs around x=3.5; all alloys of x≤3 exhibit conical anisotropy at both 295 and 77 K, and axial anisotropy for x≥3.5. Tc increases from 328 to 890 K when x varies from 0 to 3, then decreased to 564 K when x further increased to 7. The saturation magnetization, Ms, increases monotonically with increasing Fe content. A sintered magnet with a Br of 6.1 kG, a Hci of 10.6 kOe, and a BHmax of 9.1 MGOe were obtained using Pr2Co2Fe5B3.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5605-5607 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both as-cast and 1000 °C annealed RTiFe11 samples are nearly single phase with a small amount of Fe2Ti. Small amounts of Co additions do not change the microstructure, but the minor phase changed to a Fe,Co,Ti solid solution. At high Co concentration, as-cast samples are multiphase [1-12, 2-17, (Fe,Co,Ti)] and high-temperature (∼1200 °C) annealing is needed in order to produce a single-phase microstructure. Results of x-ray analysis and magnetic measurements show that YTiFe11, YTiCo11, GdTiFe11, and GdTiCo11 are uniaxial and their anisotropy fields at room temperature are 22, 18, 33, and 25 kOe, respectively. Therefore, Fe and Co sublattices are uniaxial with Fe sublattice anisotropy stronger than that of Co. In the intermediate range of composition, there is a conical-planar region for both Y and Gd systems and spin reorientations with temperature were observed. In general, the anisotropy behavior of the RTiFe11−xCox systems (R=Y,Gd) is similar but opposite to their counterpart of R2Fe17−xCox. This is due to the similarity of their crystal structure, as both are derivatives of 1-5. However, the strong contribution from the K2 anisotropy constant makes the anisotropy phase diagrams of 1-12 more complicated than those of 2-17.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4589-4591 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin reorientation transitions (SRTs) in Nd0.5Er1.5Fe14−xMxB, where M=Al or Co and x=0–3, were determined by ac susceptibility measurements. In Nd0.5Er1.5Fe14B, the SRT is observed at about 195 K. The addition of Al was found to shift the SRT to lower temperatures, presumably due to the weakening of the rare earth–transition metal exchange interaction. For M being Al and x=2, an additional SRT is observed at about 25 K, possibly due to a change of cone angle. Similar reductions in the SRT temperature were observed with Co substitution.
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