MÖSSBAUER EFFECT AND MAGNETIC PROPERTIES OF AN AMORPHOUS Fe2O3

Un oxyde amorphe de fer (III) a été préparé par décomposition thermique d'un aérosol sur un substrat chauffé. Les mesures de la susceptibilité magnétique montrent une température de Néel de 80 K. En dessous de 50 K on observe un moment thermo-remanent. Le moment paramagnétique est de 2,5 µB par ion de fer, indiquant la présence d'aggrégats antiferromagnétiques. Les spectres Mössbauer montrent un doublet paramagnétique au-dessus de 80 K avec un déplacement isomérique de + 0,15 mm/s. En dessous de 80 K une séparation hyperfine est observée avec, à 5 K, Hhf = 470 kOe et ΔEQ = 0,11 mm/s. Il en est déduit que les ions Fe3+ sont entourés par un octaèdre déformé d'ions O2-. Leurs axes de symétrie sont orientés arbitrairement dans la maille apériodique, laissant une large dispersion des angles ν entre Hhf et Vzz.An amorphous iron (III) oxide was prepared by thermal decomposition of an aerosol on a heated substrate. Magnetic susceptibility measurements show a Néel temperature of 80 K. Below 50 K a thermoremanent moment is observed. The paramagnetic moment amounts to 2.5 µB per iron ion, indicating antiferromagnetic clustering. Mössbauer spectra show a paramagnetic doublet above 80 K with an isomer shift of + 0.15 mm/s and a quadrupole splitting of 1.01 mm/s ; below 80 K a hyperfine split spectrum is found with, at 5 K, Hhf = 470 kOe and ΔEQ = 0.11 mm/s. It is derived that the Fe3+ ions are coordinated by a distorted octahedron of O2- ions. Their symmetry axes are randomly oriented in the aperiodic lattice, leaving a wide distribution of angles ν between Hhf and Vz

INITIAL SLOPE OF THE HYSTERESIS CURVE

An analytical expression for the initial slope T of the hysteresis curve is derived for a stripe domain structure in a thin magnetic film, giving that T-1 is proportional to t-1/2 (t = film thickness). This is confirmed by measurements on RF sputtered CoCr films with 20 nm ≤ t ≤ 950 nm

Magnetization processes in Co–Cr submicron samples: Hall measurements and micromagnetic simulations

The magnetization reversal of Co-G with perpendicular anisotropy is studied by anomalous Hall effect measurements and by micromagnetic simulations. In a measured hysteresis loop of a 300 nmX300 nm sample (consisting of approximately 40 columns of Co-G), discrete jumps are observed, together with a more or less continuous change in magnetization, the latter with both positive and negative sign. The continuous and discrete parts of the hysteresis loop are separated to extract micromagnetic information from the anomalous Hall measurement. The discrete jumps are attributed to parts of columns that switch irreversibly, the continuous magnetization change is attributed to reversible rotation, partly of volumes with in-plane anisotropy. These assumptions are checked by means of a micromagnetic model