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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated paramagnetism in epitaxial Co/Cu(001) films grown at room temperature in ultrahigh vacuum (UHV) using the transverse magneto-optical Kerr effect. These measurements are made possible by the very strong magnetic response of a two-dimensional (2D) paramagnet, and in this way we have extended our previous study of the thickness dependent coercivity close to the magnetic phase transition. The optical reflectivity was used to determine the thickness in reduced units d/dc to better than 10% accuracy where the critical thickness dc is determined by the onset of long-range order. In the paramagnetic region we observe a linear M-H curve with a sensitively thickness dependent saturation field Hs, which decreases to zero as the critical thickness dc is approached. At the critical point, the onset of long range order is manifested by a strongly thickness-dependent coercive field Hc, which is found to increase from zero with thickness as a power law.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5460-5462 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of fcc FexNi1−x and FexCo1−x alloys grown on Cu(100) were investigated in an element-specific fashion. The technique employed was linear dichroism in photoemission, which by varying the chirality can also determine the magnetization axis. We observed a different behavior for the two alloys at Fe concentrations above 60%. At this concentration the FexNi1−x alloy shows a strong reduction of the Fe dichroism associated with the invar instability. This is in contrast to the FexCo1−x alloy, where the Fe dichroism stays essentially constant across the concentration. Despite these differences both systems show a change of the easy axis at roughly the same electron count. For small Fe concentrations the easy axis is in-plane along the [011] direction. This changes into the [001] direction at Fe63Ni37, which is at 0.7 excess electrons per atom when compared with Fe. This is different to the bulk, where a change occurs at Fe25Ni75. We find the easy axis change for FexCo1−x to occur at 49% Fe. This would be equivalent to 0.5 excess electrons when compared with Fe. © 2000 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have grown ultrathin FexNi1−x films epitaxially on Cu(100) with different stoichiometry. Previous measurements showed a deviation of the thickness dependence of Tc for a Fe75Ni25 alloy, which was not observed for smaller Fe concentrations. Therefore, we investigated the growth near this invar concentration more closely. With a charge coupled device camera based acquisition system, we observed the evolution of the reflection high-energy electron diffraction pattern during growth near the invar concentration. This allows us to determine the in-plane lattice constant of the top layer. Up to 66% Fe content, we see in-plane lattice constant oscillations similar to the Co/Cu(100) system [Fassbender et al., Phys. Rev. Lett. 75, 4476 (1995)]. At 80% Fe content, these oscillations are suppressed and we observe also a lattice contraction as expected from recent calculations. We discuss these results in connection with our previous results on the magnetic properties of FexNi1−x ultrathin films. © 1997 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the magneto-optical Kerr effect, we have observed a striking sensitivity of the magnetic properties of ultrathin Co/Cu(001) films to submonolayer coverages of Cu. In particular large nonmonotonic changes of the coercive field Hc, the height of the M-H loop (magneto-optical signal), and the ratio S of remanent and saturation magnetizations are observed. With increasing Cu thickness the coercivity first sharply decreases, reaching a minimum at around 0.2 monolayer (ML) followed by a gradual increase. In contrast, the magneto-optical signal is found to peak strongly at the same Cu overlayer thickness of 0.2 ML, decaying in magnitude with further Cu coverage.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used scanning magneto-optic Kerr effect (MOKE) microscopy to investigate the magnetic relaxation of a polycrystalline hcp 125 A(ring) Co/Si(111) film with planar uniaxial anisotropy, on time scales between 10 and 2400 s and with a spatial resolution of 15 μm. In a static magnetic field slightly less than the coercive field and applied along the easy axis direction, domains develop and the magnetization reversal proceeds via displacements of 180° domain walls. Microscopic images of this metastable state allow the 180° domains to be identified by calibration of the MOKE signal with respect to that for the saturated magnetization states. The 180° reversed domains are observed to grow in the direction of the field in the form of narrow fingers, extending via short Barkhausen jumps, randomly spaced in time over the entire time-scale range investigated, with typical distances between pinning sites of the order of microns. This reversal behavior is qualitatively similar to that reported for Au/Co perpendicular anisotropy films a few monolayers thick.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the evolution of the in-plane magnetic hysteresis behavior of Co/Cu(001) films (in the monolayer range) by means of the transverse magneto-optical Kerr effect. Shortly after the onset of long-range order, the deposition was stopped and the almost square hysteresis loop which resulted revealed a small coercive field (Hc=0.9 G) indicating a Curie temperature Tc close to room temperature. Further Co deposition in small increments showed a dramatic increase of Hc. An increase of 9% in the thickness resulted in a variation of Hc in the range 0.9 G〈Hc〈44.6 G to which a power law of the form (d/dc−1)α with α=0.58±0.07 could be attributed. This empirical fit suggests that the dramatic increase of the coercivity is thermodynamic in origin and related to the thickness dependence of the magnetization M.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated ultrathin FexNi1−x films grown epitaxially on Cu(100) with different stochiometry. With the surface magneto-optic Kerr effect (SMOKE) we measured the variation of the Curie temperature TC as a function of the film thickness n in monolayers (ML). Using the results of our previous investigations on finite-size scaling (Huang et al.), we are able to extrapolate the value TC(∞) for samples with different Fe content. In particular, alloy films with Fe concentrations close to 65% remain ferromagnetic. This is in contrast to bulk Fe65Ni35, which shows a collapse of long range order, which is the so-called invar effect associated with a fcc to bcc structural transition. Growing these alloy films on a Cu(100) substrate forces them to adapt the Cu lattice spacing, thereby suppressing the structural relaxation. © 1996 American Institute of Physics.
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