Excess resistance and collective motion of ferromagnetic domain walls in amorphous Fe5.85Co72.15Mo2B15Si5ribbons traversed by dc electric currents

The reversal of the Hall voltage across a ferromagnetic domain wall drives a dc eddy-current loop centered on the wall, in metallic samples traversed by a dc current. The Joule dissipation in the loop leads to an additional ohmic resistance associated with walls, the "excess resistance" δR. We consider field-annealed ribbons with in-plane magnetization normal to sample length. The excess resistance δR has been measured at 300 K by removing all walls with a saturating field parallel to the domain magnetization, and looking for the corresponding decrease of resistance. The measured δR values agree within a factor of two with theoretical predlctions. At the location of each wall, the eddy-current loop generates a field parallel to the domain magnetization. These drive fields push all walls in the same direction. If the current I exceeds a critical value Ic, a collective "domain-drag" translation of the walls should occur. A collective motion of walls, induced by a dc current, has been observed in six samples by Kerr microscopy. A small 60 Hz field is used to shake walls and reduce coercivity. The sense of wall motion always reverses when the current sense is reversed, and is the conventional sense of the current. The measured values of the critical current range between 4.9 mA and 28 mA.