A. Ercole

Continuous evolution of the in‐plane magnetic anisotropies with thickness in epitaxial Fe films

We have studied the evolution of the magnetic in‐plane anisotropy in epitaxial Fe/GaAs films of both (001) and (110) 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.

Finite size effects in the static and dynamic magnetic properties of FeNi wire array structures

We report on systematic studies of both the static and dynamic properties of FeNi wire arrays on GaAs(001) substrates. The wires were between 0.4 and 10 μm wide and were separated by twice their width. The static magnetic properties were investigated using magneto optical Kerr effect magnetometry. The dynamical magnetic properties (spin-waves) were investigated by Brillouin light scattering in the Voigt geometry. With an external field applied along the hard shape axis, the saturation field was observed to increase and the spin-wave energies decreased with decreasing wire size. For fields applied along the (easy) axis of the wire, we observed an increase in the coercive field as the width of the wire is decreased. The frequency of the surface mode was found to increase with decreasing wire size while the first volume mode frequency was found to be wire size independent.

A new technique for measuring magnetic anisotropies in thin and ultrathin films by magneto-optics

A new technique for high precision measurement of magnetic anisotropy fields in thin and ultrathin films called modulated field magneto-optical anisometry (MFMA) is described. MFMA can be performed by a simple extension to a conventional magneto-optical Kerr effect magnetometer, and is therefore experimentally simple. It can resolve an arbitrary combination of anisotropies of different symmetries with a very high precision, even when there is little magneto-optical signal (e.g., ultrathin in-plane magnetized films) and high optical noise. It is spatially resolving and readily suited to the ultrahigh vacuum environment. MFMA thus offers many advantages over existing anisotropy measurement methods. A quantitative comparison is made between anisotropy field measurements made by MFMA and by Brillouin light scattering on an ultrathin Fe(001) epitaxial film. Agreement is found to within a high precision.

Direct measurement of magnetic anisotropies in epitaxial FeNi/Cu/Co spin-valve structures by Brillouin light scattering

Abstract We have determined all the relevant magnetic anisotropy fields of epitaxial FeNi/Cu/Co spin-valve structures by Brillouin light scattering (BLS). A dominant and reproducible fourfold anisotropy was found in the cobalt layer, while a weak in-plane anisotropy was observed for the permalloy layer. BLS and magnetometry measurements have been performed over the temperature range of 10–300 K.

In situ Brillouin light scattering from ultrathin epitaxial Fe/Ag(100) films with Cr and Ag overlayers

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 a...

Neutron reflectivity of single FeNi/Cu/Co trilayer spin valves

Abstract Epitaxial single trilayer FeNi/Cu/Co spin valves have been investigated using polarised neutron reflectometry (PNR). Measurements have been carried out as a function of temperature between 1.5–300 K and at RT as a function of field orientation. The results yield the magnetic moments as a function of temperature and also allow vector magnetometry to be performed.

Temperature dependence of spin waves in Co/CoO bilayers

Brillouin light scattering measurements of spin-wave frequencies in an exchange coupled ferromagnet/antiferromagnet epitaxial Co/CoO bilayer are reported. A striking temperature dependence of the measured spin-wave frequencies in the cobalt layer in the range 77–300 K was observed which has been demonstrated to be due to exchange coupling to the ultrathin (7 A) CoO layer as antiferromagnetic order develops. The temperature dependence of the spin-wave frequency demonstrates that interface exchange coupling occurs in the absence of the unidirectional anisotropy. A study of the mode line width shows a broadening with reducing temperature which indicates that locally ordered antiferromagnet regions persist above the Neel temperature and play a central role in determining the magnetic behavior of the bilayer system.