Microstructural dependence of giant-magnetoresistance in electrodeposited Cu-Co alloys

• Published in: Journal of materials science 2004-09, Vol.39 (18), p.5701-5709
• Main Authors: COHEN-HYAMS, T, PLITZKO, J. M, HETHERINGTON, C. J. D, HUTCHISON, J. L, YAHALOM, J, KAPLAN, W. D
• Format: Article
• Language: English
• Subjects: Annealing; Applied sciences; Cobalt base alloys; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Copper; Copper base alloys; Cross-disciplinary physics: materials science; rheology; Dependence; Electrodeposition; Electrodeposition, electroplating; Exact sciences and technology; Ferromagnetism; Giant magnetoresistance; Grain growth; Grain size; Magnetic properties; Magnetic properties and materials; Magnetism; Magnetoresistance; Magnetoresistivity; Magnetotransport phenomena, materials for magnetotransport; Materials science; Metals. Metallurgy; Metastable phases; Methods of deposition of films and coatings; film growth and epitaxy; Microstructure; Percolation; Physics; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Thin films
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1023/B:JMSC.0000040079.41985.6b

The relationship between the microstructure and the magnetic properties of heterogeneous Cu-Co [Cu92.5-Co7.5] (at.%) thin films prepared by electrodeposition was studied. Electron spectroscopic imaging (ESI) studies clearly revealed the evolution of the cobalt microstructure as a function of thermal treatments. The as-deposited film is composed of more than one phase; metastable Cu-Co, copper and cobalt. During annealing the metastable phase decomposes into two fcc phases; Cu and Co. Grain growth occurs with increasing annealing duration, such that the cobalt grains are more homogeneously distributed in the copper matrix. A maximum GMR effect was found after annealing at 450°C for 1.5 h, which corresponds to an average cobalt grain size of 5.5 nm according to magnetization characterization. A significant fraction of the cobalt in the Cu-Co film did not contribute to the GMR effect, due to interactions between the different magnetic grains and large ferromagnetic (FM) grains. The percolation threshold of cobalt in metastable Cu-Co alloys formed by electrodeposition is lower (less than ∼7.5 at.%) than that prepared by physical deposition methods (∼35 at.%).