Composition-Morphology-Property Relations For Giant Magnetoresistance Multilayers Grown By RF Diode Sputtering
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Composition-Morphology-Property Relations For Giant Magnetoresistance Multilayers Grown By RF Diode Sputtering W. Zou, H.N.G. Wadley, X.W. Zhou, R.A. Johnson Department of Materials Science and Engineering University of Virginia, Charlottesville, VA 22903 D. Brownell Nonvolatile Electronics, Inc. Eden Prairie, MN 55344 ABSTRACT A series of experiments have been conducted to evaluate the magnetotransport properties of RF diode sputter deposited giant magnetoresistive (GMR) multilayers with either copper or coppersilver-gold nonferromagnetic (NFM) conducting layers. The study revealed that RF diode deposited multilayers utilizing Cu80Ag15Au5 as the NFM conducting layer posses significantly superior giant magnetoresistance to otherwise identical device architectures that used pure copper as the NFM conducting layer. To explore the origin of this effect, copper and Cu80Ag15Au5 films of varying thickness have been grown under identical deposition conditions and their surface morphology and roughness investigated. Atomic force microscopy revealed significant roughness and the presence of many pinholes in thin pure copper films. The surface roughness of the Cu80Ag15Au5 layers was found to be much less than that of pure copper, and the alloying eliminated the formation of pinholes. Molecular statics estimates of activation barriers indicated that both silver and gold have significantly higher mobilities than copper atoms on a flat copper surface. However, gold is found to be incorporated in the lattice whereas silver tends to segregate (and concentrate) upon the free surface, enhancing its potency as a surfactant. The atomic scale mechanism responsible for silver’s surface flattening effect has been explored. 1. INTRODUCTION Metal multilayers consisting of alternating ferromagnetic (FM) and nonferromagnetic (NFM) metals sometimes exhibit large changes in their electrical resistance when a magnetic field is applied [1-10]. The effect results from a change in their spin dependent electron scattering when an applied magnetic field rotates the magnetic moment of one of the ferromagnetic layers [1-10]. Devices utilizing it are widely used as the magnetic field sensors in hard disk drive read heads [4]. Related devices are being investigated for use as magnetic random access memories (MRAM) [4]. Current GMR multilayers appear not to have achieved their performance upper bound. Reducing both the smoothness and chemical diffuseness of the interfaces in GMR multilayers appear to be particular important [2,8]. Achieving materials with a large GMR ratio at a low saturation field therefore requires the use of materials, layer thickness and deposition conditions that minimize interfacial roughness. 2.EXPERIMENTS The study has focused upon the influence of the nonferromagnetic conducting layer composition (either Cu or Cu80Ag15Au5) on the GMR ratio and the saturation field of RF diode sputter deposited GMR multilayers. Multilayers with either Cu or Cu80Ag15Au5 NFM T1.5.1
conducting layers together with, 100, 500 and 1000Å thick Cu and
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