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  • 1
    Electronic Resource
    Electronic Resource
    On the role of Zn in Sm2Fe17Nx permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6044-6046 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coercivities up to 1.9 T were achieved by bonding micron-size Sm2Fe17Nx particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic peak related to the melting of Zn (at 419.6 °C) was observed. In dilatometric measurements two peaks were observed for the rate of length change near the same temperatures as the DSC peaks. Polarization-versus-field curves point to an additional ferromagnetic phase with (i) a Curie temperature near 180 K and (ii) 2% of the net magnetization at low temperatures. The corresponding dip in low-temperature demagnetization curves, however, is about 10% in depth. Most of the Sm2Fe17Nx grains in the demagnetized Zn-bonded magnets are multidomain. We found γ≈3.4×10−2 J/m2 and Dc≈0.3 μm for the wall energy and for the critical single-domain particle diameter, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353464
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic reversal in Sm2Fe17Ny permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6047-6049 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Coercivity and nucleation fields for three-dimensional inhomogenities are calculated and discussed. For soft spherical inclusions in a hard magnetic matrix a (δ/R)2 dependence of the nucleation field on inclusion radius R and domain wall width δ has been obtained. To calculate propagation fields for spherical inhomogenities, a nonlinear model has been used. The corresponding coercive field can be much higher than the nucleation field, particularly if the magnitude of the anisotropy changes very steeply. Soft inclusions with sharp interfaces are ineffective at producing complete magnetic reversal. For partly nitrided particles coercivity and nucleation field are predicted to be identical, which is confirmed by experiments on high-performance Sm2Fe17N3−δ magnets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353465
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  • 3
    Electronic Resource
    Electronic Resource
    Sample size dependence of the critical current density in polycrystalline YBa2Cu3O7−δ (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2964-2968 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The zero-field transport critical current density 〈Jc〉 of polycrystalline YBa2Cu3O7−δ has been measured at 77 K for slabs of different thickness d. It was found that 〈Jc〉 increases as the thickness decreases. The experimental data is in agreement with a field-dependent Jc(H) that decreases with increasing field. However, a clear distinction between a Kim, exponential, and power law model cannot be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351501
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of magnetic methods for the determination of texture of permanent magnets : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6268-6270 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The singular point detection (SPD) technique as well as a least-mean-square procedure of fitting trial texture functions to demagnetization curves (DMC) were applied in order to determine the orientation density of the tetragonal axes of the Nd2Fe14B crystallites in sintered Nd-Fe-B magnets with different degrees of grain alignment. Both methods are less complicated than calculating the texture function from x-ray-diffraction data. The orientation densities obtained by both methods agree fairly. Analytically, they can be described as a Gaussian or a sum of cosine-power functions of the angle between the local tetragonal axis and the texture axis. This agreement is a test for the DMC method which can also be used for materials showing much larger anisotropy fields than the maximum available measuring field. The SPD and DMC methods can also be applied to measure the temperature dependence of the anisotropy field HA of the magnetic main phase in noncompletely textured polycrystalline materials. By means of the DMC method additionally the spontaneous polarization Js as well as the anisotropy constants K1 and K2 can be determined. As expected, the values of HA of our sintered Nd-Fe-B samples, measured up to 140 °C, are nearly independent of the degree of texture and are in agreement with those reported in literature. This confirms that SPD as well as DMC can be used to measure intrinsic magnetic properties for materials which can hardly be prepared as single crystals, such as interstitial compounds made by gas–solid reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358301
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  • 5
    Electronic Resource
    Electronic Resource
    Kerr microscopy observation of carbon diffusion profiles in Sm2Fe17Cx : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6717-6719 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of carbon diffusion from CH4 gas into coarse Sm2Fe17 powder on the magnetic domain structure (MDS) was studied at room temperature by means of the magneto-optical polar Kerr effect. The diffusion occurs initially along preferential paths and then through the bulk. A gradual variation in the MDS through incompletely carburized grains was observed, which reflects local changes in spontaneous magnetization and magnetic anisotropy. This suggests the existence of smooth "bathtublike'' carbon concentration profiles. An acceleration of the carburization process caused by cracking of grains during the diffusion was observed. The diffusivity R of carbon in Sm2Fe17 at 450 °C was estimated to be 2.5×10−16 m2/s. For Sm2Fe17C2.2 the domain-wall energy density is γ=3.1×10−2 J/m2, the domain-wall thickness δ=3.3 nm, the single-domain particle size Dc≈0.3 μm, and the exchange constant A=8.1×10−12 J/m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358177
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of milling on the magnetic and microstructural properties of Sm2Fe17Nx permanent magnets : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6018-6020 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By ball milling Sm2Fe17Nx the coercivity can be increased from 0.3 to 1.5 T. The coercivity increases continuously during milling up to a time of about 600 min, and then decreases for too intensive ball milling. This is connected to particle size reduction and other effects like the increase in oxygen content, introduction of mechanical stresses, formation of new grain boundaries, and amorphization of the material. Magnetic measurements, scanning electron microscopy, as well as domain wall observations indicate that long-time milled material is mainly constituted of single domain particles and isotropic polycrystalline particles with small grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355494
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  • 7
    Electronic Resource
    Electronic Resource
    Variance reduction by simultaneous multi-exponential analysis of data sets from different experiments (1991)
    Springer
    European biophysics journal 19 (1991), S. 231-240 
    Details
    ISSN: 1432-1017
    Keywords: Multi-exponentials ; Relaxation ; Data analysis ; Photocycle ; Bacteriorhodopsin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The analysis of experimental data from the photocycle of bacteriorhodopsin (bR) as sums of exponentials has accumulated a large amount of information on its kinetics which is still controversial. One reason for ambiguous results can be found in the inherent instabilities connected with the fitting of noisy data by sums of exponentials. Nevertheless, there are strategies to optimize the experiments and the data analysis by a proper combination of well known techniques. This paper describes an applicable approach based on the correct weighting of the data, a separation of the linear and the non-linear parameters in the process of the least squares approximation, and a statistical analysis applying the correlation matrix, the determinant of Fisher's information matrix, and the variance of the parameters as a measure of the reliability of the results. In addition, the confidence regions for the linear approximation of the non-linear model are compared with confidence regions for the true non-linear model. Evaluation techniques and rules for an optimum experimental design are mainly exemplified by the analysis of numerically generated model data with increasing complexity. The estimation of the number of exponentials significant for the interpretation of a given set of data is demonstrated by using records from eight absorption and photocurrent experiments on the photocycle of bacteriorhodopsin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183531
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  • 8
    Electronic Resource
    Electronic Resource
    The photocycle and the structure of iron containing bacteriorhodopsin —a kinetic and Mössbauer spectroscopy investigation (1990)
    Springer
    European biophysics journal 19 (1990), S. 11-18 
    Details
    ISSN: 1432-1017
    Keywords: Bacteriorhodopsin ; Mössbauer spectroscopy ; Cation binding site
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Bacteriorhodopsin (bR), converted by deionization to the blue form was reconstituted to the active purple membrane by the addition of Fe2+ or Fe3+ ions. 57Fe Mossbauer spectra of these samples were measured at different pH values (pH 3.9, pH 5.0 and pH 7.0) and at temperatures ranging from 4 K to 300 K. The hyperfine parameters reveal two iron environments with oxygen atoms in the neighbourhood of iron. Iron type 1 is in the 3+ high spin state. It is bound to acid side chains of the protein and/or the phosphate groups of the lipids. Iron type 2 is in the 2+ high spin state and is linked to carboxy groups of the protein in a rather unspecific way. Dynamics as measured by Mossbauer spectroscopy show that the purple membrane becomes flexible only above 220 K. At the interface between membrane and bulk water the mobility is comparable to that of proteins with hydrophilic surfaces. The photocycle of Fe 3+-bR is slowed down compared to native bR. 3–5 Fe3+/bR are sufficient to inhibit the photocycle turnover by one order of magnitude. This specific effect is also found with Cr3+, though it is less pronounced. Mössbauer spectra of Fe3+-bR at 4 K reveal that iron nuclei are spin-coupled, indicating their close spatial proximity. It is proposed that iron trinuclear clusters interact with the proton uptake site of bR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223568
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