Low Temperature Reversal in Anisotropic Ferromagnetic Films

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Easy axis reversals in permalloy films were investigated at 4 to 30°K. In contrast to films evaporated at normal incidence in the presence of a magnetic field, oblique incidence films revealed a simple motion of straight walls down to 4°K. Their velocity v was measured as a function of the applied field H, giving the dependence v ∼ exp [2 M (H − H0) V*/kT] down to 4°K. The parameters H0 and V* are explained by a model assuming a wall of nonzero width to move by thermal activation.

Thermally activated magnetic wall motion in oblique incidence films at liquid helium temperatures

Bostanjoglo

Kreisel

1970

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Superferromagnetism in thin Gd and GdAu films

Bostanjoglo

Röhkel

1971

Polycrystalline ferromagnetic Gd and GdAu films are built up of clusters, the atomic spins being exchange coupled. At low temperatures the clusters are coupled almost exclusively by magnetostatic forces. In this superferromagnetic state the usual large magnetic domains show up. At a critical temperature well below the Curie point the magnetic long‐range order is destroyed and the usual magnetic domains vanish. A short‐range order comprising several aligned neighbouring clusters, however, persists up to the Curie point. These short‐range aligned clusters form microdomains with an average diameter of 200 Å, the cluster diameter being in the order of the crystal size.

Slow wall motion in oxidized permalloy films

Charap

Fulcomer

1972

Slow domain wall motion, persisting to liquid helium temperatures, is reported for an oxidized permalloy thin film. Films protected from oxidation or reduced in dry hydrogen after oxidation fail to exhibit this phenomenon at any temperature between 300 and 5 °K. Observations are made using the magneto‐optic Kerr effect and the motion is also shown directly by a lapsed‐time photographic technique. The behavior is closely correlated with the hystersis loop contraction characteristic of the oxidized film at very low temperatures. Measured slow wall velocities range from 10−1 to 10−3 cm/s; the logarithm of the velocity varies linearly with the applied magnetic field, with a slope that increases with increasing temperature.