Negative magnetoresistance in uniaxial and amorphous ferromagnets

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Abstract
When a d.c. current crosses a 180° domain wall, the current lines are sharply bent at the wall by twice the Hall angle of the material. This is a simple consequence of Maxwell’s equations and of the existence of off‐diagonal Hall components in the resistivity tensor. In a demagnetized sample, where the current crosses many walls, the current lines follow a zigzag pattern. This leads to an increase of the effective ohmic resistance of the sample. Then a negative magnetoreistance δR/R0 should be observed if an external field parallel to the easy axis removes the walls. For a current running normal to stripe domains, we predict ΔR/R0=−β2, where β is the tangent of the Hall angle. Other kinds of domains give similar results. The present theory may explain the negative transverse magnetoresistance δR/R0=−2×10−4 associated with domains, observed recently in sputtered Gd‐Co films where ‖β‖?10−2. For very pure cobalt at 4 K (‖β‖?0.6), δR/R0?−0.4 is predicted.

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