The Effect of Domain Walls on Magnetotransport in Thin Film Fe, Co, and FePt Microstructures
1. Physikalisches Institut, RWTH Aachen, 52056 Aachen, Germany
J. Yu and A. D. Kent
Department of Physics, New York University, 4 Washington Place, New York, New York 10003, USA
L. Thomas, R. F. C. Farrow, and S. S. P. Parkin
IBM Research Division, Almaden Research Center, San Jose, California 95120, USA
The effect of magnetic domains and domain walls (dws) on spin-polarized transport has been studied in thin film Fe, Co, and FePt microstructures with controlled stripe domain configurations [1,2]. The microstructures were prepared from epitaxial bcc (110) Fe and hcp (0001) Co films which have been deposited on Al2O3 (11-20) substrates as well as epitaxial L10 (001) FePt films which have been grown on (001) MgO substrates. The (110) Fe films show a strong uniaxial component to the magnetic anisotropy with the easy axis along the  in-plane axis whereas the (0001) Co and (001) FePt films have a strong uniaxial anisotropy perpendicular to the film. The uniaxial anisotropy constants Ku (dw widths d) for the (110) Fe, (0001) Co, and (001) FePt films have been determined to 3×105 erg/cm3 (40 nm), 4×106 erg/cm3 (15 nm), and 1×108 erg/cm3 (3 nm), respectively. Varying the Fe wire width parallel to the  direction or the Co and FePt film thickness result in a continuous variation of the resulting stripe domain width (dw density).
Regarding a theory on dw scattering  the intrinsic contribution of dws to the low field magnetoresistance MR for the current perpendicular to the dw is
DR/R~ 1/d2. For (110) Fe wires due to the broad dws no intrinsic dw scattering contribution to the low field MR has been determined, whereas in Co (0001) and FePt (001) films dw scattering appears to increase the wire resistivity (Co: 0.1 % at 85 K , FePt: 0.3 % at 1.7 K).
This research was supported by DARPA-ONR, Grant No. N00014-96-1-1207. Microstructures were prepared at the CNF, Project No. 588-96.