Magnetoresistance in a deformed Cu-Ni-Fe alloy with ultrafine multilayer structure
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R. Ramesh Bellcore, Red Bank, New Jersey 07701 (Received 12 August 1993; accepted 24 January 1994)
The creation of a giant magnetoresistance (GMR) effect in a spinodally decomposed and deformed Cu-20% Ni-20% Fe alloy is reported. The alloy is processed to contain a locally multilayered superlattice-like structure with alternating ferromagnetic and nonmagnetic layers with a size scale of 10-20 A. The microstructural modification produced a dramatic improvement in room-temperature magnetoresistance ratio from —0.6 to —5%. The observed magnetoresistance is most likely related to the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase, although the exact mechanism involved may be qualitatively different from the usual GMR picture. A rather unusual temperature-dependence of magnetoresistance ratio, i.e., the room-temperature value being greater than that at 4.2 K, was found.
I. INTRODUCTION The electrical resistivity of a metal is changed when an external magnetic field is applied. In normal (nonmagnetic) metals, this "normal" magnetoresistance effect is caused by the Lorentz force that curves the electron trajectories. In magnetic metals and alloys, the same effect is present, but the magnetoresistance is dominated by the interaction of the conduction electrons with localized magnetic moments (associated with the d or f electrons) that are oriented by the applied field.1 In most of the ferromagnetic metals, the electrical resistivity measured along the field direction (pB) increases with the applied field (positive magnetoresistance) as shown schematically in Fig. 1. At low fields, the resistivity change is primarily due to the spontaneous resistivity anisotropy (p increases when p ± is replaced with Pn, i.e., by orientation of the magnetization along the direction of electrical conduction). At higher fields beyond the saturation of magnetization, Hs, only the normal magnetoresistance (which is also positive) remains to cause the resistivity change. The giant magnetoresistance (GMR) phenomenon has been discovered in recent years in Fe/Cr, Co/Cu, and various other multilayer superlattice films,2"9 as well as in heterogeneous (granular) Co-Cu thin films and ribbons.10"12 Unlike the typical bulk ferromagnetic metals and alloys, these multilayer films exhibit electrical resistivity that decreases with magnetic field (negative
a)Present
address: Kaoshiung Polytechnique Institute, Ta-Hsu Hsiang,
Taiwan. 1134
J. Mater. Res., Vol. 9, No. 5, May 1994
http://journals.cambridge.org
Downloaded: 16 Mar 2015
Spontaneous - Resistivity Anisotropy
Normal Resistivity
H FIG. 1. Schematic magnetoresistance behavior in ferromagnetic metals and alloys. p\\ and pL are the resistivity measured parallel and perpendicular to the field direction, respectively.
magnetoresistance). The resistivity change is typically in the range of 5-50%. The GMR effect offers a possibility of convenient magnetic sensing, e.g., as a high resolution transducer (read head) for magnetic information storage systems. The pos
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