Annealed Cu/Co/Cu/NiFe/FeMn Spin Valves: Nanostructure and Magnetism
- PDF / 483,314 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 105 Downloads / 166 Views
ANNEALED Cu/Co/Cu/NiFe/FeMn SPIN VALVES: NANOSTRUCTURE AND MAGNETISM C. MENY*, J.P. JAY*, P. PANISSOD*, P. HUMBERT*, V.S. SPERIOSU', H. LEFAKIS', J.P. NOZIERESA+ AND B.A. GURNEYL *IPCMS, UMR 46 CNRS, 4 rue Blaise Pascal, 67070 Strasbourg, France AIBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 951206099, USA 'Present address: Laboratoire de Magn~tisme Louis N6el, UPR 5051 CNRS, BP 166X, 38042 Grenoble, France. ABSTRACT Magnetic, magnetotransport and structural properties of Cu/Co/Cu/NiFe/FeMn spinvalve structures were studied before and after sequential annealing in the temperature range 240-360°C. Since no extended interdiffusion is observed, the overall deterioration of the magnetic and magnetoresistive properties of the spin valve is believed to originate from morphological and structural changes. In particular, annealing was found to decrease the magnetoresistive properties of Co as a result of structural changes within the Co layer and at the Co/Cu interface. These changes are accompanied by modifications of the magnetic properties. For annealing temperatures above 240'C, strong grain growth within the Co layer and increasing amount of fcc Co explain the increased magnetic hardness of this layer. INTRODUCTION Since its discovery, many efforts have been made to understand the fundamental mechanisms of giant magnetoresistance. Its origin is now widely believed to be spin dependent scattering (SDS) [1-8]. The influence of the detailed bulk and interface structure of metallic multilayers and sandwiches is well accepted too. The nature of the SDS was shown to be either interfacial [1,2,5-7], bulk [3,4] or both [7], depending on the materials involved. In systems with interfacial SDS, the structural properties of the interface such as interface roughness or compositional intermixing play a dominant role. In Fe/Cr multilayers for example, the magnetoresistance amplitude is increased by interface roughening [8,7 In sputtered NiFe/Cu/NiFe/FeMn spin valves, the role of compositional intermixing at the NiFe/Cu interfaces has been recently studied by systematically increasing the thickness of the intermixed regions through successive annealings [10-14]. In contrast to Fe/Cr, interface roughening decreases the magnetoresistance amplitude. The observed decrease was attributed to the presence of high resistivity compositionally intermixed layers at the NiFe/Cu interfaces. Spin independent scattering within these non-magnetic, Cu-rich, intermixed layers reduces both the number and the mean free path of the electrons exchanged between the two ferromagnetic layers. In this paper, we report the effect of annealing on the magnetic, magnetotransport and structural properties of Co/Cu/NiFe/FeMn spin valves. The results were obtained by conventional magnetometry and transport measurements and by zero field59Co NMR. They were interpreted in the light of measurements of nonferromagnetic interfacial layers on annealed Cu/Co/Cu structures [10], of extensive studies of annealed NiFe/Cu/NiFe/FeMn spin valves [
Data Loading...
