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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1667-1673 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Isotropic nanocrystalline exchange coupled FeNdB magnets with enhanced remanence were produced using the melt spinning procedure. Starting from nearly single phase Fe14Nd2B magnets, the content of additional α-Fe in composite magnets was stepwise increased up to 40 vol % by reducing the Nd and B content. The maximum remanence of JR=1.25 T was found in composite magnets containing 30 vol % α-Fe, the maximum energy product reaches the value (BH)max=185 kJ/m3, whereas the coercive field is μ0HC=0.53 T for this composition. The microstructural investigations of the composite magnets reveal two characteristic maxima in the grain size distribution at about 15 and 25 nm corresponding to the α-Fe phase and to the Fe14Nd2B phase, respectively. The influence of the exchange coupling on the coercive field can be described by a microstructural parameter αex. From the temperature dependence of the coercive field the microstructural parameters αKαex and Neff are determined. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5380-5382 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of internal stress on the magnetic anisotropy and the magnetostriction was investigated in sputter-deposited amorphous (Tb0.27Dy0.73)0.42Fe0.58 films. Films with tensile stress show in-plane anisotropy and giant magnetostriction of λ(parallel)=400×10−6 at 1 T measured in a field parallel to the film plane at room temperature. The magnetostriction rises rapidly to λ(parallel)=200×10−6 at 0.05 T and the coercivity is less than 0.01 T. On the other hand films with compressive stress show perpendicular anisotropy and still higher magnetostriction of λ(parallel)=540×10−6 at 1 T; however, this is by far a slower increase of magnetostriction at small fields. This different behavior is explained by considering the nature of magnetization processes, i.e., domain-wall motion and spin rotation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micromagnetic calculations using a finite element technique rigorously describe the magnetic properties of novel, isotropic rare-earth-based composite magnets. Numerical results obtained for a composite material of Nd2Fe14B, SmCo5 or Sm2(Fe0.8Co0.2)17N2.8 and α-Fe particles show that remanence, coercivity, and coercive squareness sensitively depend on microstructural features. Interparticle exchange interactions enhance the remanence by about 60% with respect to noninteracting particles for a mean-grain size approaching the exchange length of the soft magnetic phase and a significant percentage of α-Fe. On the other hand, exchange interactions between the phases suppress the nucleation of reversed domains and thus preserve a high coercive field. Therefore, optimally structured, isotropic composite magnets show remarkably high energy products exceeding 400 kJ/m3.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5143-5145 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the influence of the nanocrystalline microstructure on the magnetic properties of pure nanocrystalline metals, in situ magnetic measurements of high-purity nanocrystalline nickel, prepared by a gas-condensation technique with subsequent compaction at various pressures have been performed. The approach to ferromagnetic saturation indicates free volumes in the nanocrystalline system of the size of individual missing crystallites as well as internal stresses. While the saturation polarization of the nanocrystalline Ni samples appears to be unchanged compared to coarse-grained Ni the coercive field and magnetic domains are strongly influenced by the nanocrystalline structure. The shape of the domains with sizes of 10–200 μm much larger than the crystallite size depends on the annealing state of the specimen. The initial coercive field increases with the compaction pressure during preparation. Upon annealing it further increases to a maximum value at Ta=500 °C and decreases at higher annealing temperatures. Additionally, the effect of oxygen located in the grain boundaries has been studied. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 488-491 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of Ga substitution on the magnetocrystalline anisotropy of Sm2Co17−xGax (x=5,6) compounds has been investigated by means of x-ray diffraction (XRD) and magnetic measurements. XRD patterns show that the samples studied here crystallize in the rhombohedral Th2Zn17-type structure. The Curie temperature for Sm2Co12Ga5 and Sm2Co11Ga6 is 367 and 166 K, respectively, according to thermal-magnetic curves. XRD measurement on the magnetically aligned sample shows that the room temperature easy magnetization direction of Sm2Co12Ga5 compound corresponds to the c axis. The spin-reorientation transition is observed at 32 K for Sm2Co11Ga6. The anisotropy constants K1 and K2 of Sm2Co17−xGax (x=5,6) were derived by fitting the magnetization recoil curve measured between 5 K and their Curie temperature. An anomalous jump in magnetization is found in the magnetization curve of Sm2Co12Ga5 compound. In order to investigate the temperature dependence of the critical field Hcrit in which the jumps of magnetization occur, hysteresis loops were measured in a field range of −90–90 kOe between 5 and 150 K. The critical field is found to shift rapidly to lower value with increasing temperature. © 2001 American Institute of Physics.
    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 86 (1999), S. 3274-3277 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phase formation and magnetic properties of melt-spun Sm2Fe15Ga2Cx ribbons with a Zr addition of 1.5 at. % have been investigated. A metastable phase with the disordered TbCu7-type structure is formed in the samples annealed at temperatures between 620 and 740 °C. Upon heating above 750 °C, a structural transformation from the hexagonal TbCu7- to the rhombohedral Th2Zn17-type structure occurs. It was found that the Zr addition improves the thermal stability of the TbCu7 structure. Transmission electron microscopy observations show that the grain sizes in 1:7-type ribbons are much smaller than that in 2:17-type samples. The highest value of the maximum energy product of 88.7 kJ/m3 is obtained in a 1:7-type ribbon annealed at 740 °C for 15 min. The corresponding remanence and coercivity amounts to 0.8 and 0.43 T, respectively. In contrast, coercivities higher than 0.8 T obtained in 2:17-type ribbons are accompanied by remanences lower than 0.66 T. The 1:7-type ribbons with grain sizes in the range of 15–45 nm show significant remanence enhancement which can be attributed to the exchange coupling between adjacent grains. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2781-2786 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe–Tb–Dy/Finemet™ and Fe–Tb–Dy/Fe multilayers have been prepared by ion beam sputtering on room temperature sapphire substrates (Finemet is a nanocrystalline Fe–Si–B–Nb–Cu magnetic alloy). After production, the Fe–Tb–Dy and the Finemet layers are amorphous, whereas the Fe layers are polycrystalline. Subsequent annealing leads to relaxation of the amorphous Fe–Tb–Dy layers in both cases and to crystallization of the Finemet layers for the Fe–Tb–Dy/Finemet multilayers. In this regime, the properties of the multilayers can be well described by a mixture rule of the two perfectly coupled components. In an optimum thickness range for both layers, they show very soft magnetic properties and high magnetoelasticity. Furthermore, it has been observed that crystallization of the Fe–Tb–Dy layers within the multilayer is hindered by interface stabilization as recently predicted in U. Herr, H. Geisler, H. Ippach, and K. Samwer, Phys. Rev. B 59, 13719 (1999). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5507-5507 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic aftereffects (MAEs) of the initial reluctivity have been measured over times of 1–106 s in the as-quenched state of amorphous alloy Fe40Ni40P14B6 at 500 K. A considerable decrease in the relaxation amplitude observed for times t〉103–10 s has been interpreted in terms of a superposition of two different mechanisms resulting from (i) quasi-reversible, local rearrangements of two-level systems, and (ii) irreversible, wide-range order relaxation due to the migration of free volumes.2 Here we report on the results obtained from fractal analysis of the short-time MAE region (t(approximately-less-than)200 s). Fitting of the stretched exponential,3 exp[−(t/τ)ρ], (0〈β〈1), to the experimental data yielded values of ρ in the range 0.15–0.30. This implies a spectral (fracton) dimension d˜ of 0.3–0.6 for this alloy. In terms of a postulated ultrametric distribution of random energy barriers, this means a hierarchy with a low degree of ramification (Z∼1.2).
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6618-6622 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of M(M=Zr, Cu, Nb) additives on the stability and magnetic properties of melt-spun nanocrystalline Sm2Fe15Ga2C3 ribbons with the 1:7-type structure has been investigated. The addition of 1 at. % of Zr or Nb was found to improve the thermal stability significantly, but the addition of Cu was found to decrease the thermal stability of the 1:7 metastable phase. After an appropriate heat treatment, M (Zr, Nb, or Cu)-containing samples exhibit better hard magnetic properties than the M-free sample. The intrinsic coercivity and maximum energy product were found to increase from 3.6 kOe and 59 kJ/m3 for the M-free sample to 4.8 kOe and 88 kJ/m3 for the Zr-containing one. The exchange interaction between the grains or the "exchange spring" behavior is studied according the Kneller and Hawig model and Henkel's plot. The enhancements of magnetic properties originate from the improvement of the intrinsic magnetic properties as well as the refinement of the microstructure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6690-6696 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-phase LaNi6.1 and LaNi9.2 films with hexagonal TbCu7 structure have been successfully obtained. Films in the micron scale range were deposited by ion beam sputtering on sapphire and glass substrates heated at 600 K. A two-material La–Ni mosaic target was used for this purpose. X-ray diffraction and transmission electron microscopy investigations show that the lattice parameters of the hexagonal structure follow a linear dependence for Ni concentration. This result relates to a random substitution of La atoms for Ni dumbbell pairs in the ordered CaCu5 structure. The films exhibit a strong preferential orientation, with the c axis parallel to the substrate plane, which seems to be favored by the presence of Ni dumbbell pairs. The expected impact of this phase on the preparation of new hydrogen storage materials is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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