Thermally activated reversal in exchange-coupled structures

In this paper, we study the thermally activated reversal of IrMn/CoFe exchange-coupled structures using Lorentz microscopy and magnetometry. An asymmetry and a training effect were found on the hysteresis loops both with and without holding the film at negative saturation of the ferromagnetic layer. Holding the film at negative saturation results in the hysteresis loop shifting toward zero field. We believe that, in this system, two energy barrier distributions with different time constants coexist. The large-time-constant thermally activated reversal of the antiferromagnetic layer contributes to a increasing shift of the entire hysteresis loop toward zero field with increased period of time spent at negative saturation of the ferromagnetic layer. The small-time-constant thermal activation contributes to asymmetry in the magnetization reversal and training effects

Optical and magneto-optical properties of thin films for high density information recording

It was found that optical and magneto-optical (MO) properties of thin film materials have potential application for blue laser recording. For this purpose, we have used a combination of ellipsometric and polar MO Kerr effect measurements. The optical and magneto-optical properties of Mn(Sb₁-xBix) and Co-Pt nanocrystalline films were investigated for incident photons in the energy range from 1.3 to 4.0 eV. A large Kerr rotation angle of about 0.570 was observed at photon energy hw»2.65 eV for the Mn₅₅Sb₃₆Bi₉ film with an average grain size of 30 nm. The changes of the exchange splitting and the spin-orbit interaction strength are responsible for the strong dependence of Kerr effect in Mn(Sb₁-xBix) nanocrystalline films. It was shown that the large MO polar Kerr rotation angle is correlated with a perpendicular magnetic anisotropy in nanocrystalline Co₃Pt film

Magnetization reversal in the pinned layer of CoFe/PtMn bilayers

The magnetization reversal of the ferromagnetic (FM) layer in CoFe/PtMn exchange-coupled bilayer films has been investigated using bulk magnetometry. These films exhibit very complex angular dependence and the easy axis is perpendicular to the field applied during deposition and post-annealing. Holding the film at negative saturation of the FM layer for up to 17 h results in no change in the exchange field. We believe that this is a thermally stable exchange-coupled system. Only limited thermal activation with a small time constant appears and no thermally activated reversal of the antiferromagnetic layer with a large time constant exits

ATOM PROBE CHARACTERISATION OF Co/TRANSITION-METAL MULTILAYER STRUCTURES

Cobalt/transition-metal multilayer structures grown on Co field-ion specimens have been analysed by both conventional atom probe (AP) and the position-sensitive atom probe (POSAP). The combination of the two techniques allows the chemical abruptness and the roughness of the interfaces to be studied independently, and can be supported by high resolution transmission electron microscope (HREM) studies of multilayers deposited simultaneously on flat substrates. Layered structures can be formed with sharp interfaces, with epitaxial growth having been observed, even when using only a simple thermal evaporation source. However, growth by this method seems to be somewhat inconsistent, with carbon contamination leading to the formation of interdiffused, and in the extreme even amorphous layers. With the use of electron beam sources in place of filament evaporators, this technique should provide a powerful complement to the more conventional characterisation methods

The role of the laser fluence on the Al2O3 target in the nanostructure and morphology of VOx:Al2O3 thin films prepared by pulsed laser deposition

The role played by the laser fluence on the Al2O3 target when depositing VOx:Al2O3 nanocomposite thin films by alternate ablation from ceramic alumina (Al2O3) and metallic vanadium (V) targets in vacuum has been studied. The fluence and number of pulses on the V target to prepare the nanoparticles has been maintained constant, while the fluence used to grow the Al2O3 host has been varied from 1.3 to 3.9 J cm-2. The optical properties of the films, namely in-situ reflectivity during growth and extinction coefficient, evidence that the properties of the nanoparticles change as a function of the laser fluence on the Al2O3 host. Transmission electron microscopy analysis shows the formation of vanadium oxide nanoparticles with average diameters in the range of 4.6 nm. Structural analysis of the nanoparticles shows that they are mainly crystalline. Phases of VOx with average [O]/[V] ratios from 1.7 to 2.2 have been identified with the most commonly observed being V3O5. This is in agreement with low heat of formation of this oxide. It is shown that the oxidation of the nanoparticles induced during the deposition of Al2O3 is very efficient since no metallic V nanoparticles are formed even for the lowest fluence used. © 2007 Elsevier B.V. All rights reserved.This work was partially funded by CICYT (Spain), under MAT2003-01490 and TEC2006-04538 projects. The electron microscopy analysis was performed at Argonne National Laboratory, this facility is supported under contract DE-AC02-06CH11357 between UChicago Argonne, LLC and the DOE. S. N.-S. acknowledges the Ministerio de Educación y Ciencia for the support of a FPU grant.Peer Reviewe