Magnetic properties of nanostructured CoSm/FeCo films

Abstract

${\mathrm{Co}}_{80}$ ${\mathrm{Sm}}_{20}$/${\mathrm{Fe}}_{65}$ ${\mathrm{Co}}_{35}$ bilayer and multilayer films with Cr underlayers and overlayers have been fabricated and studied. All the samples prepared have in-plane anisotropy and the hysteresis loops were simple single loops for ${\mathit{t}}_{\mathrm{FeCo}}$≤300 Å indicating that the two phases are strongly exchange coupled. The magnetization of these samples is found to increase with increasing FeCo layer thickness for a fixed CoSm layer thickness. The coercivity, anisotropy constant, and anisotropy field for films with fixed CoSm layer thickness were found to decrease with increasing FeCo layer thickness. The magnetization squareness values of the hysteresis loops in the direction parallel to the film plane, for different CoSm and FeCo layer thicknesses, were found to be close to S≊0.75. The energy products for these samples vary from about 6 MG Oe at room temperature to 26 MG Oe at 30 K. The shape and the behavior of the initial loops and the minor loops suggest that wall pinning is the dominant coercivity mechanism in these films. Reversible demagnetization curves were measured and found to be consistent with the behavior expected for ‘‘exchange-spring’’ magnets.