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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 347-355 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the evolution of the magnetic in-plane anisotropy in epitaxial Fe/GaAs films of both (001) and (1¯10) orientation as a function of the Fe layer thickness using the longitudinal magneto-optic Kerr effect and Brillouin light scattering. Magnetization curves which are recorded in situ during film growth reveal a continuous change of the net anisotropy axes with increasing film thickness. This behavior can be understood to arise from the combination of a uniaxial and a cubic in-plane magnetic anisotropy which are both thickness dependent. Structural analysis of the substrate and Fe film surfaces provides insight into the contribution of atomic steps at the interfaces to the magnetic anisotropy. Changing the degree of crystalline order at the Fe–GaAs interface allows us to conclude that the magnetic anisotropies are determined by atomic scale order. © 1996 American Institute of Physics.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the magnetization reversal and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 and 27 A(ring)) trilayer structures prepared by MBE on a 500-A(ring) Ge/GaAs(110) epilayer. We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal MOKE measurements. For the samples examined, coherent rotation of the magnetization vector is observed when the magnetic field is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths. An absence of antiferromagnetic (AF) coupling has been observed previously [W. F. Egelhoff, Jr. and M. T. Kief, Phys. Rev. B 45, 7795 (1992)] in contrast to recent results, indicating that AF coupling [M. T. Johnson et al., Phys. Rev. Lett. 69, 969 (1992)] and GMR [D. Grieg et al., J. Magn. Magn. Mater. 110, L239 (1992)] can occur in Co/Cu(111)/Co structures grown by MBE, but these properties are sensitively dependent on growth conditions. The absence of coupling in our samples is attributed to the presence of a significant interface roughness induced by the Ge epilayer. The uniaxial anisotropies are assumed to arise from strain or defects induced in the film.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the magnetic properties of ultrathin epitaxial Fe/Ag(100) films by means of in situ Brillouin light scattering (BLS) in an ultrahigh vacuum chamber equipped with magneto-optic Kerr effect, low energy electron diffraction, and reflection high energy electron diffraction instruments. Our novel in situ BLS system allows us to perform measurements rapidly, in order to avoid surface contamination, and hence to observe the evolution of the spin-wave frequency with increasing film thickness. Good reproducibility is observed between different growth runs. The direction of the applied field within the film plane has been varied revealing that the magnetocrystalline anisotropy has cubic symmetry and that there is no observable in-plane uniaxial anisotropy. From the values of the hard and easy axis spin wave frequencies we have determined the values of the in-plane fourfold anisotropy and effective demagnetizing fields during the growth of 13.9 monolayer (ML) Fe films. The evolution of the fourfold anisotropy is in reasonable agreement with that reported by other researchers. The effect of depositing Cr and Ag overlayers onto the completed 13.9 ML film has also been studied. We have deduced values for the surface anisotropy constants for the Fe/Ag and Fe/vacuum interfaces and we compare these with previously reported values. A qualitatively different evolution of the spin wave frequency with overlayer thickness is observed for the deposition of Cr and Ag, which may be related to the magnetic properties of the Cr overlayer. © 1996 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss the use of room temperature polar magneto-optic Kerr effect (MOKE) measurements at high field (≤7 T) in investigating antiferromagnetic (AFM) and ferromagnetic (FM) exchange coupling in MBE-grown wedged trilayers. In the case of Co/Cu/Co(111), the polar MOKE revealed the first AFM coupling peak at 9 A(ring) Cu thickness and the second weaker AFM coupling peak at 20 A(ring). This is an important result because it helps in resolving the present controversy over whether oscillatory coupling exists in (111) oriented MBE-grown Co/Cu/Co structures. For Fe/Cr/Fe(001), polar MOKE is found to be less sensitive than in-plane MOKE for extracting the detailed form of the coupling. However, polar MOKE reveals additional variations in the perpendicular saturation fields as a function of interlayer thickness, which are not found in the in-plane MOKE saturation fields.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6670-6678 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interlayer exchange coupling has been investigated in epitaxial Fe(20 A(ring))/Cr/Fe(20 A(ring))/Ag/GaAs(100) structures that contain a wedge-shaped (0–40 A(ring)) Cr layer. Longitudinal and polar magneto-optical Kerr-effect (MOKE) and Brillouin light-scattering measurements have been combined to determine values for the relevant anisotropy constants and both the bilinear and biquadratic coupling strengths. The phase and period of the oscillations in the interlayer coupling are found to agree well with those reported by other researchers while the total coupling strength is found to be reduced. This reduction is presumably due to the presence of structural imperfections in our samples, and our results may therefore be of use in testing some of the recently proposed extrinsic biquadratic coupling mechanisms. Specifically, we find that for the Cr thicknesses studied the biquadratic coupling strength in our samples varies as d−1.4Cr where dCr is the thickness of the Cr layer. We also present results that show how the ultrathin Cr limit may be investigated. We show that the coercivity of the easy axis MOKE loops is sensitive to submonolayer coverages of Cr and that polar MOKE is sensitive to the strong ferromagnetic coupling found in the 0–4 A(ring) Cr thickness range. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we present the results of a detailed study of the switching behavior observed in epitaxial single Fe films of thickness between 30 and 450 A(ring), and a wedge shaped Fe film with a thickness range of 10–60 A(ring) grown on GaAs (001). These films have cubic and uniaxial anisotropies which change with film thickness. For the fixed thickness films the values of the anisotropy constants were accurately determined by Brillouin light scattering (BLS) measurements together with polar magneto-optic Kerr effect (MOKE) measurements that gave the value of the magnetization. The switching behavior of these samples was observed with in-plane MOKE magnetometry as a function of the angle between the applied field and the in-plane crystallographic axes. Measurements of the component of magnetization perpendicular to the applied field allow a precise determination of the relative orientation of the hard and easy in-plane anisotropy axes. This can be used to accurately determine the ratio of uniaxial to cubic anisotropy constants, when this ratio is less than one. The ratios obtained from MOKE agree well with those obtained from BLS. Minimum energy calculations predict that the reversal process should proceed by a continuous rotation of the magnetization vector with either one or two irreversible jumps, depending on the applied field orientation and the nature of the anisotropy of the film. The calculations provide a good qualitative description of the observed reversal process, although the magnetic microstructure influences the exact values of the switching fields.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5301-5303 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been found recently that the magnetic surface anisotropy Ks in Fe70B30/Ag multilayer films decreases monotonically with magnetic layer thickness (2L) for 2L〈16.5 A(ring). In order to determine possible effects of the spacer material on the surface anisotropy in the aforementioned system, Ag has been replaced with Al2O3 and ferromagnetic resonance (FMR) measurements have been made on these films. These Fe70B30/Al2O3 films were fabricated by magnetron sputtering and were characterized by x-ray-diffraction and vibrating sample magnetometer (VSM) measurements in addition to FMR. In the region where Ks depends upon 2L, the data is insufficient to confirm the thickness dependence of Ks that was observed in Fe70B30/Ag, while in the region where Ks is independent of 2L, the values of Ks deduced for Fe70B30/Ag and Fe70B30/Al2O3 are in good agreement. The latter is particularly interesting in light of the enormous difference in conductivity between Ag and Al2O3.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5683-5683 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In searching for a possible dependence of magnetic surface anisotropy on film thickness, the magnetic surface anisotropy constant Ks of compositionally modulated amorphous Fe70B30-Ag films1 was measured by means of a method2 involving the dependence of the ferromagnetic resonance (FMR) fields on the magnetic layer thickness 2L. The ratio of the Ag to the Fe70B30 thickness was 3 to 1 while 2L ranged from 1.6 to 90 A(ring). Measurements were made with the applied static magnetic field parallel and perpendicular to the plane of the sample, at both X- and K-band frequencies for at least 14 values of 2L in each case. The results of magnetization measurements, made by SQUID magnetometry, have already been reported.1 Using the measured values of the thin-film magnetization and the aforementioned method, the value of Ks has been determined over the entire range of 2L. The results are consistent with a constant value of Ks for 2L〉16.5 A(ring), while Ks is found to decrease monotonically as 2L is reduced from 16.5 to 1.6 A(ring). A similar decrease of Ks is found even if the bulk value rather than the thin-film values of the magnetization is used throughout. In addition, the value of Ks has been deduced for 2L=4.1, 6.7, 10.2, and 16.7 A(ring), from the original SQUID data. These values are in good agreement with those determined by the FMR method.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6692-6694 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The rise and damping of spin excitations in three Ni81Fe19 films of thickness 50, 500, and 5000 Å have been studied with an optical pump–probe technique in which the sample is pumped with an optically triggered magnetic field pulse. The motion of the magnetization was described by the uniform mode solution of the Landau–Lifshitz–Gilbert equation. The rise time of the pulsed field within the film was smallest in the 50 Å sample and was generally greater when the pulsed field was perpendicular to the film plane. The damping constant was smallest in the 500 Å sample. The variations in the rise time and damping are attributed to the presence of eddy currents and structural disorder in the films. Under certain excitation conditions a second mode was observed in the 5000 Å sample which we believe to be a magnetostatic surface mode. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4580-4582 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical pump–probe spectroscopy has been used to observe damped ferromagnetic resonance (FMR) oscillations in thin film Fe samples. The FMR was pumped by magnetic field pulses generated by an optically triggered photoconductive switch, and probed by means of time resolved measurements of the magneto-optical Kerr rotation. The photoconductive switch structure consisted of a parallel wire transmission line, of 125 μm track width and separation, defined on a semi-insulating GaAs substrate. The biased transmission line was optically gated at one end so that a current pulse propagated along the transmission line to where the sample had been overlaid. The magnetic field associated with the current pulse is spatially nonuniform. By focusing the probe beam on the sample at different points above the transmission line the effect of the orientation of the pump field has been studied. The gyroscopic motion of the magnetization has been modeled by solving the Landau–Lifshitz–Gilbert equation and the magneto-optical response of the sample has been calculated by taking account of both the longitudinal and polar Kerr effects. The calculated and measured magneto-optical Kerr rotations are found to be in reasonable agreement. © 1999 American Institute of Physics.
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