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Notes: We have used the magneto-optical Kerr effect to study the thickness dependence of the perpendicular magnetic anisotropy, coercivity, nucleation field and remanence in an ultrathin Co wedge (0–9 monolayers) grown epitaxially on Pt(111) and capped by a thin Pt overlayer. In addition, the spin-reversal mechanism in the Co layers has been investigated using Kerr domain imaging. The sample showed perpendicular magnetization up to an extrapolated Co thickness of 15 monolayers (ML), with derived volume and interface anisotropy constants of −0.77 MJ/m3 and 1.15 mJ/m2, respectively. The Kerr rotation and Kerr ellipticity demonstrated linear dependences on the Co thickness (tCo), with sizeable extrapolated offsets at tCo=0, attributed to polarization of the Pt by the Co. The coercivity (Hc) and nucleation field both rose to peak values at tCo=1.5 ML, with a subsequent monotonic fall-off for higher Co thicknesses. In the case of Hc, this fall-off did not demonstrate the tCo−5/2 dependence shown by a similar Pd(111)/Co/Pd sample investigated earlier.

Notes: A unique sample was prepared on a Cu(100) single crystal, consisting of three Co layers separated by two Cu layers in the form of wedges oriented perpendicular to each other: Cu(100)/80 A(ring) Co/Cu wedge A/30 A(ring) Co/Cu wedge B/30 A(ring) Co/7 A(ring) Cu/30 A(ring) Au. Position-sensitive magneto-optical Kerr effect measurements along Cu wedge B, at a fixed position on Cu wedge A corresponding to maximum antiferromagnetic (AF) coupling, enabled us to investigate not only the AF but also the ferromagnetic (F) coupling between the two 30 A(ring) Co layers as a function of the Cu thickness. The measurements confirmed both long and short period coupling oscillations in the AF regime, and revealed the predicted extension of the short period through the F regime.

Notes: A Pd/Co double layer has been grown epitaxially in ultrahigh vacuum on a Pd(111) single crystal, with the Co in the shape of a wedge of thickness varying from 0 to 10 monolayers (ML). The polar magneto-optical Kerr effect has been used to make a nearly continuous set of measurements of the magnetic properties as a function of Co thickness tCo. The coercive fields Hc and nucleation fields Hn show large, well-defined maxima at tCo∼2.3 ML. Between 4 and 9 ML, we find that Hc falls with increasing thickness according to a tCo−5/2 dependence. The Kerr ellipticity and Kerr rotation depend linearly on Co thickness above ∼2 ML Co, but show appreciable offsets when extrapolated to tCo=0. These offsets are clear evidence of the polarization of Pd near the interfaces. Extensive in situ growth studies of the structure of the films are also reported.

Notes: Two series of thin-film diodes (TFDs), used as switching elements in active-matrix liquid-crystal displays, have been prepared with various amorphous-silicon-nitride (a-SiNxHy) thicknesses. In a first series, with thin top metal contacts, it was observed by photon-emission spectroscopic analysis that both the effective electron temperature and the number of hot electrons increased as the nitride thickness (at constant field) or the electric field across the TFD (at constant nitride thickness) increased. A further analysis revealed that for the thicker samples, the electrons became progressively hotter on moving from the cathode to the anode. In a second series, the drift of the TFD current–voltage characteristic under dc-driving conditions has been monitored as a function of nitride thickness at various fields. The anodic drift, resulting from defect-state creation in the anodic sample region, and the field and thickness dependence of the hot-electron intensity, show very similar trends. Therefore, it is concluded that the anodic drift is driven by hot-electron-induced defect-state creation. Also, it was found that optical phonon scattering effectively limits the electron temperature up to a field of around 1.5 MV/cm, while for larger field strengths impact ionization appears a probable additional energy-loss mechanism. For the anodic drift in a TFD with an a-SiNxHy layer thickness of 104 nm, a comparable critical-field strength of around 1.5 MV/cm was determined, below which an efficient electron–phonon scattering mechanism strongly limits the production of hot electrons. For a decreasing amorphous-layer thickness, the critical-field strength increases. As a result, an improved lifetime of a-SiNxHy TFDs in their application has been obtained using a small amorphous-layer thickness. © 2001 American Institute of Physics.

Notes: Magnetic anisotropies of ultrathin transition-metal films are inherently related to their structural properties. In ultrathin films the large fraction of atoms located at the film interface generates strong interface anisotropies, whereas elastic strain fields caused by the forced registry of atoms at the substrate/film interface induce magnetoelastic anisotropy contributions. So far the experimental confirmation of the transition from these thin-film properties to bulk anisotropy properties, characterized by a dominating magnetocrystalline anisotropy, has not yet been presented. Magnetic anisotropies reflect, depending on their origin, both the crystallographic symmetry and the symmetry of the film geometry. For a clear separation between magnetoelastic, magnetocrystalline and Néel-type interface anisotropy contributions, the film symmetry and thickness must be chosen such that the respective different anisotropy contributions appear with different symmetries and film thickness dependencies. This is the case for (110)-oriented fcc Co films. In the present study we use the Brillouin light-scattering technique for the determination of the anisotropy contributions. An analysis of the spin-wave frequency measured as a function of the in-plane direction of the external field and the film thickness yields information about all relevant anisotropies. The samples used were molecular-beam-epitaxy grown in ultrahigh vacuum. Onto a Cu (110) single-crystal substrate a wedge-type sample and two staircase-shaped samples with distinct thicknesses in the range of 8–110 A(ring) were grown.To obtain symmetric Co/Cu interfaces the Co layers were covered with a 12 A(ring) Cu layer. Finally, a 25-A(ring)-thick Au protective layer was deposited. Low-energy electron-diffraction studies were used to obtain the structural data of the films. All relevant anisotropy contributions—the magnetocrystalline anisotropy, and the uniaxial in-plane and out-of-plane anisotropy contributions—were determined. Three different anisotropy regimes are observed as a function of the Co layer thickness dCo. This thickness regime up to 13 A(ring) is dominated by the magnetoelastic anisotropy contributions as a result of the pseudomorphic film growth of the Co layer. For Co layer thicknesses larger than 13 A(ring) we find a reduction of the magnetoelastic anisotropy contributions. This is structurally correlated to an anisotropic relaxation of the in-plane Co lattice constant. In the regime of dCo(approximately-greater-than)50 A(ring) we observe a thickness-independent value for the magnetocrystalline anisotropy contribution K1=−8.5×105 erg/cm3. This anisotropy contribution is largely suppressed for dCo〈50 A(ring). This finding might either indicate a breakdown of the usually postulated linear superposition principle of magnetic anisotropy contributions to the free anisotropy energy, or it might point to a subtle modification of the electronic band structure. At the onset of the magnetocrystalline anisotropy we find a change in the easy magnetization direction from 〈001〉 for thin Co films to 〈111〉 for thicker ones. For a more detailed discussion see Ref. .

Notes: A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness has been observed. The Co thickness dependence displays two clear peaks consistent with the recently predicted oscillation period of 6.2 A(ring) Co. Apart from the two peaks also several small peaks are visible on a scale of about 1 monolayer Co. Free-electron calculations indicate that these rapid variations in strength may result from slight differences between the slopes and starting points of the two Co wedges that were involved in the experiment.

Notes: The exchange biasing field (Heb) and coercive field (Hc) of molecular-beam-epitaxy-grown Cu/Ni80Fe20/Fe50Mn50 samples in [111], [001], and [110] orientations have been investigated by longitudinal Kerr effect measurements. Ni80Fe20 and Fe50Mn50 were deposited as orthogonal wedge-shaped layers on single-crystal Cu substrates in a magnetic field, enabling the study of the thickness dependence of Heb and Hc on a single sample for each orientation. A strong dependence of Heb and Hc on the growth orientation is observed. The results are interpreted in terms of the observed noncollinear spin structure of the antiferromagnet and a comparison is given with the predictions from recent theoretical models.

Notes: We discuss the fabrication and microstructuring techniques of pillar structures made of high vacuum sputtered Fe/Cr multilayers and of molecular beam epitaxy evaporated Co/Cu multilayers, for which we measured the giant magnetoresistance effect with the current perpendicular to the multilayer plane from 4 K to 300 K. Using optical lithography and reactive ion etching techniques we obtained structures with a typical height of 0.5 μm and a width ranging between 3 and 10 μm. For both Fe/Cr and Co/Cu multilayers we find an enhanced magnetoresistance with respect to the in-plane case. The perpendicular magnetoresistance of the Fe/Cr pillars strongly decreases with temperature, while for the Co/Cu samples the temperature dependence is weaker, indicating electron-magnon scattering processes of different strength.

Notes: Photon-emission experiments on silicon-rich hydrogenated amorphous silicon-nitride metal–semiconductor–metal diodes, have shown the existence of hot electrons under applied field strengths of approximately 106 V/cm. The effective temperatures and mean free path between collision for the electrons were estimated from the spectra. It is shown that, in general, asymmetrical changes in the electrical characteristics of the devices occur after prolonged dc stressing at high fields. Two drift mechanisms can be distinguished. The first is called "cathodic'' drift and is driven by recombination between band-tail carriers in the semiconductor. The other is called "anodic'' drift, and results from the effects of hot electrons at the anode. The spatial and time dependence of these drift mechanism is explained using a simple model. © 1996 American Institute of Physics.

Notes: Magnetic anisotropies and misfit strain relaxations have been investigated in Cu/Ni-wedge/Cu (100) and (111) sandwiches deposited by molecular beam epitaxy on single-crystal Cu substrates. Our results reveal a clear distinction in the nature of the measured anisotropy at Ni thicknesses below and above the critical value tc, where the growth becomes incoherent. Below tc, coherent lattice strain modifies only the volume anisotropy, while interface anisotropy is Néel type; above tc, magnetoelastic effects are found to contribute to the interface anisotropy.