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  • Articles: DFG German National Licenses  (54)
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  • Articles: DFG German National Licenses  (54)
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  • 1
    Electronic Resource
    Electronic Resource
    Mössbauer study of the surface crystallization of the amorphous and nanocrystalline Fe81Zr7B12 alloy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3422-3425 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The combined conversion electron emission and γ-transmission Mössbauer spectroscopy is used to investigate the differences in the bulk and surface crystallization of the amorphous Fe81Zr7B12 alloy in which the nanocrystalline bcc-Fe was formed due to annealing. The measurements were performed for Fe81Zr7B12 ribbons in the as-quenched state and after 1 h annealing at 430, 500, 550, 600, and 780 °C. The clear differences in the surface and bulk crystallization behaviors were detected. Not only does the surface crystallization start at lower annealing temperature than the bulk one, but additional phases were detected at the surface which do not form in the bulk. The enhanced surface crystallization was attributed to the boron depletion of the surface region which leads to the decrease of the crystallization temperature at the surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363209
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  • 2
    Electronic Resource
    Electronic Resource
    Role of alloying elements in the stability of nitrides in nitrogen- implanted α-Fe (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1312-1321 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The role of alloying elements, such as Cr, Al, Ti, and Mn, in the formation and stability of the nitride phases formed due to nitrogen ion implantation into metallic α-iron was studied by conversion electron Mössbauer spectroscopy. The thermal stability of the nitride phases of α-Fe implanted with N was greatly increased by coimplanting with N the alloying elements. For instance, the stability of α'-martensite at low N-dose implantation is strongly enhanced and also that of γ'-Fe4N at high N dose. Titanium stabilizes the ε-Fe3−xN-type nitride preventing the formation of the γ' phase. The presence of alloying elements influences the thermal stability of nitrides by increasing their binding energy and thus preventing the dissociation of nitrogen and also by forming traps that lead to the formation of TiN, AlN, or CrN nitrides. The thermal stability of nitrides, especially of ε-Fe3−xN and γ'-Fe4N ones, is improved in decreasing order by the presence of Ti, Al, Cr, and Mn. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360373
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  • 3
    Electronic Resource
    Electronic Resource
    Mössbauer study of ion-beam mixing of Fe/Zr multilayers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5232-5241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ar-ion-beam mixing of Fe/Zr multilayers is studied in detail by conversion electron Mössbauer spectroscopy (CEMS) and x-ray diffraction (XRD). The dependence of the ion-beam induced amorphization and interfacial mixing on the sublayer thickness and ion dose (1×1013–2×1016 Ar/cm2) is studied systematically for samples with Fe to Zr thickness ratios dFe/dZr=1 and 0.5 and modulation wavelengths Λ=dFe+dZr of 5–80 nm and 7.5–90 nm, respectively. The CEMS results allowed the evaluation of the mixing efficiency from the thickness of the mixed layers. The experimentally determined mixing efficiency was compared with theoretical estimates based on the ballistic collision and thermal spike models, showing good agreement with the predictions of the modified ballistic collision model. For high degrees of amorphization the composition of the amorphous phase formed due to ion-beam mixing is close to the nominal composition of the sample, as revealed by CEMS measurements. These results were compared with those obtained for amorphous Fe-Zr alloys formed by vapor deposition. The XRD results fully agree with CEMS measurements and show that due to ion irradiation the amorphous Fe-Zr phase is formed. The XRD results show that a change of texture occurs from Zr(002) to Zr(100) in the samples with small Λ irradiated with high ion dose. XRD reveals in these samples the formation of the ZrO2 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357173
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  • 4
    Electronic Resource
    Electronic Resource
    Mössbauer and x-ray study of the structure and magnetic properties of amorphous and nanocrystalline Fe81Zr7B12 and Fe79Zr7B12Cu2 alloys (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 993-1003 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The specialized technique of radio-frequency-induced collapse of Mössbauer spectra combined with conventional Mössbauer spectroscopy, x-ray diffraction (XRD), small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) are used to investigate in detail the magnetic and structural properties of the two magnetic materials Fe81Zr7B12 and Fe79Zr7B12Cu2. Thermal treatments to convert the as-quenched, fully amorphous state into mixtures of nanocrystalline and amorphous states and the effect of the small Cu addition were of primary interest due to the improved magnetic behavior in the mixed state. DSC shows that the Cu leads to a lowering of the onset temperature for formation of the nanocrystalline phase and also to an increase in the range of temperatures over which this phase forms. XRD and Mössbauer data show the nanoscale phase to be bcc Fe and the Mössbauer spectral parameters demonstrate it to be essentially pure Fe (i.e., with little or no Zr, B, or Cu substitutional impurities). The electron density contrast between the amorphous matrix and the bcc Fe permits the detection of the Fe grains by SAXS and significant volume fractions with sizes of only 2.8–8 nm are shown to exist. Larger sizes are also present as demonstrated by the XRD and Mössbauer data and a bimodal size distribution is suggested. The Mössbauer experiments in which the radio-frequency-induced effects (rf collapse and rf sidebands) are used, allows the nanocrystalline bcc phase to be distinguished from magnetically harder microcrystalline α-Fe. The complete rf collapse of the magnetic hyperfine structure occurs only in the amorphous and nanocrystalline phases and is suppressed by the formation of larger grains. The rf sidebands disappear when the nanocrystalline phase is formed, revealing that magnetostriction vanishes. The rf-Mössbauer studies are shown to be particularly sensitive to magnetic softness of the material in that large changes in the spectra are observed for applied field changes as small as 2 Oe. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360885
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  • 5
    Electronic Resource
    Electronic Resource
    Mössbauer study of the magnetic properties of nanocrystalline Fe80.5Nb7B12.5 alloy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4427-4429 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nanocrystalline body-centered-cubic (bcc)-Fe phase was formed by controlled 1 h annealing of the amorphous Fe80.5Nb7B12.5 alloy at temperatures ranging from 490 to 650 °C. The microstructure and magnetic properties of the nanocrystalline alloy were investigated by Mössbauer spectroscopy, differential scanning calorimetry, and quasistatic hysteresis loop measurements. Conventional Mössbauer spectroscopy allowed identification of phases and the determination of their relative content. The specialized radio frequency (rf)-Mössbauer technique, which employs the effects induced by the rf magnetic field (rf collapse and rf sideband effects) allowed us to distinguish the magnetically soft amorphous and nanocrystalline phase from the magnetically harder microcrystalline Fe. The rf-Mössbauer experiments performed as a function of the rf field intensity allowed determination of the anisotropy fields in each phase of the nanocrystalline alloy (amorphous matrix, nanoscale bcc-Fe grains). The measurements of the hysteresis loops versus annealing temperature revealed minimum coercivity (0.15 Oe) at 610 °C. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370363
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  • 6
    Electronic Resource
    Electronic Resource
    Mössbauer study of the influence of thermal treatment on giant magnetoresistance and interface structure in Fe/Cr multilayers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5039-5041 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the giant magnetoresistance effect (GMR) on the interface structure in Fe/Cr multilayers was studied by magnetoresistivity and Mössbauer spectroscopy. The Fe/Cr multilayers consisting of Fe(6 nm)+[Cr(1.1 nm)/Fe(3 nm)]60+Cr(1.1 nm) were deposited by dc magnetron sputtering. Samples were annealed for 1 h at temperatures ranging from 200 to 500 °C. The interface structure was characterized by conversion electron Mössbauer spectroscopy (CEMS). Various different Fe sites: the bulk, step and perfect interface positions were identified. The evolution of the fraction of Fe atoms in different environments vs annealing temperature revealed that annealing at 300 °C induces bulk and in-plane diffusion of atoms. Higher annealing temperature causes substantial roughening of the interface related to a strong bulk diffusion of atoms. Microstructural changes observed in the CEMS spectra correspond well to the GMR measurements which reveal an enhancement of magnetoresistivity in Fe/Cr multilayers annealed at about 300 °C and its decrease due to deterioration of the interface at higher annealing temperatures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370084
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  • 7
    Electronic Resource
    Electronic Resource
    Modification of the short range order in amorphous alloys induced by the swift heavy ion irradiation (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 74-80 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental evidence of the changes of the short range order (SRO) in amorphous alloys due to high energy deposition in electronic processes related to the slowing down of swift heavy ions is presented. Modification of the local structure was studied by the specialized "rf-Mössbauer" technique in amorphous Fe40Ni35Si10B15, Fe73.5Nb3Cu1Si13.5B9, Fe73.5Nb4.5Cr5Cu1B16, and Fe80.5Nb7B12.5 alloys irradiated at low temperature with 6 GeV Pb ions. The changes of SRO were studied as a function of ion fluence (from 1×1011 to 2.4×1013ions/cm2) and electronic energy deposition rate for the amorphous Fe40Ni35Si10B15 alloy. The effects observed were interpreted in relation to the anisotropic growth of the amorphous samples. A novel effect consisting of partial surface crystallization induced by swift heavy ion irradiation was observed in the Fe90Zr7B3 alloy by conversion electron Mössbauer spectroscopy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376406
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  • 8
    Electronic Resource
    Electronic Resource
    Ion-beam mixing and solid-state reaction of Fe-Zr multilayers (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4363-4370 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The amorphization of an Fe-Zr multilayer film due to ion-beam mixing with protons and due to solid-state reaction is studied in detail using backscatter Mössbauer spectroscopy, x-ray diffraction, and Auger electron spectroscopy. The local structure of the amorphous phase produced by both processes is found to be very similar based on the Mössbauer results. The dose dependence of the ion-beam-mixed phase fraction can be accounted for approximately by a collision cascade mixing model. Incomplete amorphization of the Fe was observed as a result of the proton irradiation with a large enough dose to produce apparent saturation whereas complete amorphization occurred for the identical multilayer structure via solid-state reaction. The latter was characterized by a thermal activation energy of 0.7 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354403
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  • 9
    Electronic Resource
    Electronic Resource
    Study of the nanocrystalline Fe73.5Nb4.5Cr5Cu1B16 alloy by the radio-frequency-Mössbauer technique (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 935-940 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of Cr on the structural and magnetic properties of iron based amorphous and nanocrystalline alloys is studied for the Fe73.5Nb4.5Cr5Cu1B16 alloy by an unconventional technique which combines the Mössbauer spectroscopy with the effects induced by the radio-frequency (rf) magnetic fields (rf collapse and rf sideband effects). The nanocrystalline bcc-Fe phase, formed by annealing the amorphous precursor for 1 h at temperatures 490 °C–550 °C, was embedded in the retained amorphous matrix. The conventional Mössbauer measurements allowed the identification of three types of phases in the nanocrystalline alloy: (i) the retained amorphous matrix, (ii) the nanocrystalline bcc-Fe phase, whose abundance increased with increasing annealing temperature, and (iii) the interfacial phase formed at the bcc-Fe grain boundaries. The rf collapse effect observed in the Mössbauer spectra of the samples exposed to the rf field of 60.9 MHz permits the study of the magnetic anisotropy in all phases present. The rf collapse effect occurs only in the amorphous phase, thus revealing that the magnetic anisotropy of the amorphous matrix is significantly smaller than that encountered in the nanocrystalline phase. The rf-Mössbauer experiments performed as a function of the rf field intensity allowed the determination of the distributions of the anisotropy fields in the nanocrystalline-amorphous composite alloy. The rf sidebands effect reveals a strong reduction of magnetostriction related to the formation of the nanocrystalline phase. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366781
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetism and nanostructure of Fe93−x−yZr7BxCuy alloys (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 1747-1758 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A set of Fe-based amorphous alloys, Fe93−x−yZr7BxCuy, with x=4, 6, 8, or 12, and y=0 or 2 has been systematically characterized in their ability to form nanocrystalline, magnetically soft material via annealing in the range of 430–600 °C. Conventional Mössbauer spectroscopy is used to follow the degree of bcc-Fe formation as well as changes in the hyperfine field distribution of the amorphous phase as a function of anneal temperature. Copper plays a strong role in the bcc-Fe formation for x=12 but less of a role for x=8 and 6. Unconventional Mössbauer studies utilizing radio frequency (rf) fields provide information on the soft magnetic nature of the alloys by observing the degree of rf-induced collapse of the hyperfine fields. The Mössbauer experiment in which the rf collapse and rf sideband effects are used allows the soft nanocrystalline bcc phase to be distinguished from magnetically harder microcrystalline α-Fe. The rf Mössbauer technique, being particularly sensitive to the magnetic anisotropy, provides information on the anisotropy fields and hence on the grain size distribution. X-ray diffraction (XRD) is used to estimate the bcc-Fe grain size based on the diffraction peak linewidths. Average grain sizes of 5–14 nm are found for 500–550 °C annealed specimens where smaller grain sizes are always observed for y=2 compared to y=0 for fixed x. Small-angle x-ray scattering is also used to study the grain size and this method yields sizes in the range from 3 to 7 nm, consistently almost a factor of 2 smaller than those from the XRD line broadening. This discrepancy is attributed to the difference in the regions of the 20-μm-thick ribbons probed by the two methods. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365976
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