J. Ferré

MAGNETIC SWITCHING AND IN-PLANE UNIAXIAL ANISOTROPY IN ULTRATHIN AG/FE/AG(100) EPITAXIAL FILMS

We have studied the process by which the in‐plane magnetization of an ultrathin (4–11 ML) epitaxial iron film reverses under the action of an external magnetic field. Kerr effect measurements reveal a small in‐plane uniaxial anisotropy superimposed on the cubic magnetocrystalline anisotropy which greatly influences the reversal. In addition, we find that depending upon the field orientation, reversal can proceed either via a ‘‘1‐jump’’ mechanism, by the sweeping of 180° domain walls and which gives a classic square hysteresis loop, or by a ‘‘2‐jump’’ mechanism, by the sweeping of 90° domain walls at two distinct applied field strengths—this gives a more unusual hysteresis loop with two irreversible transitions. We have developed a simple phenomenological energy model which explains how so small a uniaxial anisotropy can play so significant a role in the reversal process. The model explains the two reversal mechanisms and predicts with good experimental agreement which should be observed for different appl...

Magnetically textured γ-Fe2O3 nanoparticles in a silica gel matrix: Optical and magneto-optical properties

Optical and magneto-optical properties of maghemite superparamagnetic particles dispersed (f=0.28 vol % γ-Fe2O3) in a silica gel matrix have been studied at room temperature in the 1.5–3.7 eV spectral range. A permanent optical anisotropy can be induced when applying a magnetic field during the sol-gel freezing process. The permanent linear dichroism and birefringence in such in-plane magnetically textured samples are attentively studied. The spectral dispersion of Faraday effects in our textured samples is analyzed taking into account the in-plane optical anisotropy. Such a composite material is a promising candidate for future magneto-optical applications.

Magnetically textured γ-Fe2O3 nanoparticles in a silica gel matrix: Structural and magnetic properties

This paper is devoted to magnetic and structural properties of anisotropic γ-Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the r...

Observation of magneto-optical second-harmonic generation with surface plasmon excitation in ultrathin Au/Co/Au films

Magnetization-induced second-harmonic generation with surface plasmon excitation in an ultrathin Au/Co/Au multilayer structure has been investigated. The resonant coupling of surface plasmons with the fundamental light results in drastic changes of the second-harmonic intensity and a sign reversal of nonlinear magneto-optical effects. Model analysis of the observed phenomena is given on the basis of the multiple interference of interface nonlinear contributions calculated using the Green’s functions formalism.

Light‐induced magnetic effects in an insulating spin glass

We report on the photoinduced magnetic phenomena in an insulating spin glass, the cobalt alumino silicate glass (13.3 at. % Co) below its freezing temperature Tf =5 K. In particular the illumination of the sample by near infrared radiation speeds up the relaxation of the thermoremanent magnetization, and enhances significantly the magnetic susceptibility near and below Tf. We proposed a simple phenomenological model which explains why the magnetic metastability is strongly affected by light illumination. The temperature and magnetic field dependence of the photomagnetic effects are also discussed.

Magnetooptic Observation Of Domains At Low Temperature In The Transparent Ferromagnet LiHoF[sub]4[/sub]

The capability of magnetooptic microscopy has been improved considerably thanks to the use of CCD cameras and digital image processing. Using Faraday-effect, we observed the evolution of the magnetic domain structure in the dipolar uniaxial ferromagnet LiHoF4 at very low temperatures (below Tc = 1.54 K) and determined its (H, T) magnetic phase diagram. The possibility of digital image averaging and image substraction increases significantly the sensitivity of the microscopic observation. This is illustrated by the ability to visualise the domain structure near Tc, where contrast is very low. Scanning over the depth of the specimen allows, in simple cases, the determination of the 3-dimensional domain shape. We shall discuss the nucleation process of magnetic bubbles in very thick samples (up to 2mm) from spike shaped domains originating near their surface.

Magnetization-induced second harmonic generation imaging of buried magnetic interfaces

Magnetization-induced second harmonic generation is selectively sensitive to the magnetization of surfaces or buried interfaces. We have used it to obtain images covering areas up to 100 micrometers wide of the magnetic domain structures of Fe/Pd and Co/Pt buried interfaces with a micrometer resolution.

Magnetization-induced second harmonic generation in ultrathin Au/Co/Au films

Ultrathin magnetic cobalt-based Au/Co/Au trilayers have been studied by the optical second harmonic generation (SHG) and by the linear magneto-optical Kerr effect (MOKE). We show that SHG has a selective interface and surface sensitivity, whereas MOKE is bulk-sensitive. SHG was used to probe the surface plasmon resonance in Au/Co/Au films. The resonant coupling of surface plasmons with SHG, results in an enhancement and sign reversal of nonlinear magneto-optical effects. Model calculations of the observed phenomena are given on the basis of a nonlocal field theory, which permits to distinguish the different interface contributions to SHG.