Low Temperature Reversal in Anisotropic Ferromagnetic Films

The magnetic reversal of anisotropic iron and 83% Ni—17% Fe films was studied by Lorentz microscopy at 4 to 300 °K. Below 15 °K for permalloy and 30 °K for iron the usual Barkhausen jumps vanish. In permalloy now wall motion at constant field consisting of tiny jumps (≪ 0.5 μm) sets in at a critical field. Below the critical field wall deflections are reversible. In iron the low temperature wall motion consists of short circle Bloch line jumps (≪ 0.1 μm), formation of small bordering domains and their reversal by rotation. These processes take place in constant fields.