We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal magneto-optic Kerr effect measurements. This arrangement differs from the usual procedures in that the same optical geometry is used but the magnet geometry altered. This leads to two magneto-optic signals which are directly comparable in magnitude thereby giving the in-plane magnetization vector directly. We show that it is of great value to study both in-plane magnetization vector components when studying coupled structures where significant anisotropies are also present. We discuss simulations which show that it is possible to accurately determine the coupling strength in such structures by examining the behavior of the component of magnetization perpendicular to the applied field in the vicinity of the hard in-plane anisotropy axis. We illustrate this technique by examining the magnetization and magnetic anisotropy behavior of ultrathin 0 0Co/Cu(111)/Co (dc"=20A and 27 A) trilayer structures prepared by molecular beam epitaxy, in which coherent rotation of the magnetization vector is observed when the magnetic field B 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.
A technique for engineering micron and submicron scale structures from magnetic films of transition metals has been developed using a combination of electron- and ion-beam lithography enabling high-quality arrays of submicron magnetic Fe wires to be fabricated. This process can be used to fabricate novel devices from a variety of metal combinations which would not be possible by the usual liftoff metallization method. The structure and magnetic properties are reported of an epitaxial 25 nm Fe(001)/GaAs(001) film and the wire gratings which are fabricated from it. The width of the wires in the grating is 0.5 μm for all structures studied, but the separation of each wire is varied in the range 0.5 to 16 μm. An artificially induced shape anisotropy field of around 1 kG, consistent with a magnetostatic calculation, was observed for all separations studied. The field dependence of the magneto-optic Kerr effect and magnetoresistance (MR) data is consistent with a twisted magnetization configuration across the width of the sample beneath saturation for transverse applied fields. In this case, the detailed form of the field dependence of the MR is strikingly modified from that observed in the continuous film and is consistent with coherent rotation of the magnetization.
We have shown that rotons as well as phonons can evaporate 4 He atoms in a singlequantum process. Measurements of the time of flight and the angular distribution of the evaporated atoms clearly distinguish between evaporation by phonons and rotons. The results indicate that energy and the parallel component of momentum are conserved at the free liquid surface.PACS numbers: 67.20. + k, 43.35.+d, 62.60. + v We have recently shown that He atoms can be evaporated by phonons in liquid 4 He in a singlequantum process in which one phonon evaporates one He atom. 1 In this Letter we report measurements of the angular distribution of 4 He atoms evaporated by a beam of phonons and rotons which are incident at an angle of 13° to the normal to the free surface. This distribution can be understood in terms of the boundary conditions at the surface. This, together with the good agreement between the measured and calculated times of flight, allows us to conclude that 4 He atoms are evaporated by rotons as well as phonons in a quantum interaction in which an excitation in the liquid is annihilated and an atom in a free state is created.The evaporation of liquid 4 He has been discussed for many years. 2,3 Interest in it was rekindled by the work of Johnston and King 4 who attempted to measure the velocity distribution of atoms evaporating from liquid 4 He at 0.6 K, although their results turned out to be incorrect. 5 They apparently saw a spectrum of atoms with characteristic temperature (1.5 K) well above that corresponding to the liquid temperature (0.6 K). This stimulated 6,7 explanations in terms of a roton, at the roton minimum energy A, giving its energy to an atom in the liquid which after evaporation would have kinetic energy equal to A -E B = 1.5 K, where E B is the latent heat per atom. The large number of rotons at this energy (8.65 K) where the density of states is infinite was thought to give rise to a dominant number of atoms with energy 1.5 K. However, Cole 8 pointed out that these rotons, although numerous, have a low attack frequency on the interface because their group velocity tends to zero. In fact, the effect of the density of states and group velocity cancel each other. More recent measurements 5,9,10 have shown that evaporated 4 He atoms do have energies commensurate with the temperature of the liquid.The important suggestion made by Anderson 6 and Hyman, Scully, and Widom 7 that a single excitation could evaporate a single atom was tested by Balibar et al.However, at the low temperatures T < 0.3 K which are needed for long phonon mean free paths, they were unable to detect atoms evaporated by phonons. The signals which they ascribed to roton-atom desorption lead to a maximum velocity for these rotons of 160 msec -1 . This is a mysterious result for which no convincing reason could be given. We now believe that they used heater powers which were too high, as we find that the detected atom-signal changes shape for powers above 10 mW mm -2 and it appears slower than those for lower powers. We can reproduce t...
Epitaxial Co has been grown on GaAs(001) and studied by both low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED), and by the magneto-optic Kerr effect (MOKE) and polarized neutron reflection (PNR). Three samples were fabricated using different growth procedures: (1) ‘‘interrupted’’ growth (including an anneal); (2) and (3) continuous growth of similar thicknesses. For sample 1, RHEED patterns indicate an initial growth in the bcc phase followed by a relaxation into a distorted single phase at completion of growth, whereas samples 2 and 3 showed a multicrystalline structure after growth. LEED patterns were used to check the existence of the 2×4 reconstruction patterns before growth, but no LEED patterns could be obtained after more than 2 Å Co was deposited, in contrast to the RHEED patterns which remained visible throughout the growth. Structural analysis of the completed films indicates the formation of a ∼10 Å CoO layer on the Co/air interface, and gives thicknesses for magnetic material of (1) 30 Å and (2) 80 Å. Sample 1 showed a dominant fourfold magnetic anisotropy with the easy axis parallel to the (100) direction and with a strength 2K4/M of ∼0.5 kOe, smaller in magnitude than that reported for bcc films on GaAs(110) but along the same axis [G. A. Prinz et al., J. Appl. Phys. 57, 3672 (1985)]. However, samples 2 and 3 showed only a large uniaxial anisotropy along the (110) direction of strength 2K1/M of ∼1.5 kOe and ∼2.5 kOe, respectively, similar in magnitude to those previously observed [G. A. Prinz et al., J. Appl. Phys. 57, 3676 (1985)]. We attribute the origin of the contrasting magnetic anisotropy behavior observed to the differences in final structure.
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