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  • 1
    Electronic Resource
    Electronic Resource
    Nucleation of reversed domains at grain boundaries : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6510-6512 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micromagnetic analysis using a finite-element technique confirms that intergrain magnetostatic and exchange interactions drastically affect the magnetization reversal mechanism in nucleation controlled permanent magnets. The investigation of the nucleation fields of magnetically coupled grains emphasizes the important role of nonmagnetic boundary phases and well-aligned grains for the enhancement of coercivity. The long-range magnetostatic interactions between the grains reduce the coercive field of ideally oriented particles. The exchange coupling of misoriented neighboring grains causes a strongly inhomogeneous magnetic state near the interface of the particles which favors the nucleation of reversed domains. Intergrain exchange interactions considerably reduce the coercive field, especially if the angle between the easy axes of adjacent grains is high. An algorithm for adaptive mesh refinement controls the discretization error throughout the calculation of the demagnetization curves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352597
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  • 2
    Electronic Resource
    Electronic Resource
    Coercivity of Sm-Fe-N ferromagnets produced by the mechanical alloying technique (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6791-6797 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sm-Fe-N permanent magnets have been prepared by mechanical alloying of Sm and Fe powder and subsequently treating the material in a two-step process. Measurements of the minor hysteresis loops and of the initial magnetization curve were performed at room temperature. The reversible susceptibility (χrev), the total susceptibility (χtot) of the initial magnetization curve and of the demagnetization curve, and the temperature dependence of the coercive field (Hc) of a magnetically isotropic nanocrystalline Sm-Fe-N magnet have been measured up to a field strength of 6.4 MA/m. The anisotropy constants, K1 and K2, of Sm2Fe17Nx were deduced from the crystalline electric field calculation in the temperature range from 0 to 500 K. The critical diameter of single domain Sm-Fe-N particles was calculated to be 320 nm at room temperature. This leads to the conclusion that mechanically alloyed Sm-Fe-N is composed of single-domain particles. The temperature dependence of the coercive field of Sm-Fe-N has been analyzed within the framework of the micromagnetic models. It is concluded from these results that the nucleation process controls the coercivity mechanism of mechanically alloyed Sm-Fe-N material. The thermostability of the Sm-Fe-N magnet has also been tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355079
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of magnetic relaxation in YBa2Cu3O7−δ leading to temperature-independent activation energies (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1936-1939 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Within the framework of first-order kinetics the activation energy spectrum p(U) for thermal activated flux motion in YBa2Cu3O7−δ single crystals is derived from the time decay of the magnetic polarization μ0M(t). The distribution function p(U) turns out to be temperature independent, so that the time dependence of μ0M(t,T) can be described by one unique spectrum p(U) in the whole temperature range 0 〈 T 〈 Tc. Concerning the crystal directions H(parallel)cˆ and H⊥cˆ, respectively, a threshold energy in the case H⊥cˆ is noticed which may be related to the Peierls potential, formed by the Cu-O planes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351668
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic domain observation in amorphous wires : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5357-5359 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The domain patterns of as-cast Fe-rich amorphous wires with 125 μm in diameter and a length of 10 cm have been observed by means of magneto-optical Kerr effect. Particular attention is paid to the observation of domains at the end and inside the wire after adequate polishing procedures. Four distinguishable regions within the wire namely, the shell, the core with diameter between 60 to 80 μm, and two different closure domain structures at the end of the wire depending on the two different remanent states, are observed. Investigating one end of the wire, we found conical-like domains with increasing diameter reaching at least several hundred μm into the wire in one remanent state, in the other remanent state we find a very small conical-like domain with decreasing diameter reaching only several ten μm into the wire. In addition, reversed domain patches inside the core up to a distance of about 3 cm from both ends can be observed. These results give a hint to enlighten the origin of the switching mechanism and its recently found alternating directional propagation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353730
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of inverse domains in high Tc superconductors (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1478-1485 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nucleation of domains of inverse polarity is observed in the remanent state of high Tc superconductors using the high-resolution Faraday effect (HRF). The remanent state consists of domains with trapped flux and of domains with opposite polarity, separated from each other by an annihilation zone. It is shown that the stray fields of microstructural defects contribute to the nucleation process. Using the capability of the HRF technique to observe dynamic processes, experimental evidence for the different signs of the vortices is given. The influence of the pinning forces on this behavior is also shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351712
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of Ga substitution on the magnetocrystalline anisotropy of arc-melted Sm2Co17−xGax (x=5,6) compounds (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 488-491 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.1328063
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of additives on the structure and magnetic properties of 1:7 type Sm2Fe15Ga2C3 permanent magnets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6618-6622 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.1289796
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  • 8
    Electronic Resource
    Electronic Resource
    Structure and magnetic properties of Zr-doped nanocrystalline Sm2Fe15Ga2Cx ribbons (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3274-3277 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.371201
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  • 9
    Electronic Resource
    Electronic Resource
    Preparation of highly overstoichiometric LaNi5+x (1≤x≤4) single-phase films by ion beam sputtering (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6690-6696 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.371745
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy and giant magnetostriction of amorphous TbDyFe films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5380-5382 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.357192
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