Low Temperature Motion of Néel and Bloch Walls

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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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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.

Possible tunneling in ferromagnetics with extraordinary viscosity

Bostanjoglo

Gemünd

1973

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The velocity of extraordinary viscous wall motion occuring in oxide contaminated ferromagnetic films was measured as a function of magnetic field and temperature in the range 3.2 to 23 K. Down to the lowest temperature the velocity depends exponentially on the field. There is, furthermore, a transition temperature below which the usual marked temperature dependence abruptly stops. The experimental results are explained by assuming relaxing oxide particles with a volume spread to introduce time dependent terms in the wall potential via exchange coupling to the ferromagnetic. Because of the above transition the oxide particle relaxation is believed to proceed both by thermal excitation and a tunneling process.