Combined Spin Valve and Anisotropic Magnetoresistance in NiFe/Cu/NiFe Layered Thin Films

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COMBINED SPIN VALVE AND ANISOTROPIC MAGNETORESISTANCE IN NiFe/Cu/NiFe LAYERED THIN FILMS Th.G.S.M. RIJKSab, R. COEHOORNb AND W.J.M. DE JONGEa aEindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands bphilips Research Laboratories, P.O. Box 80000, 5600 JA Eindhoven, The Netherlands ABSTRACT We present a theoretical study of the combined effect of spin valve and anisotropic magnetoresistance in NiFe/Cu/NiFe layered thin films, using an extended form of the semiclassical Camley and Barrels model for electron transport. The anisotropic magnetoresistance is treated by introducing spindependent anisotropic mean free paths in the NiFe layers. From calculations of both magnetoresistance effects as a function of NiFe and Cu thickness, we discuss the validity of a description of the combined effect in terms of a simple summation of spin valve and anisotropic magnetoresistance. INTRODUCTION Recently Dieny et al. reported on the magnetotransport properties of Ni 80Fe 20/Cu/Ni 80Fe2,/Mn50 Fe50 layered thin films"' 2. The low field magnetoresistive behaviour of these layered systems may be advantageous for application in magnetoresistive readback heads, which are an important element of high density magnetic recording 3. Recent measurements on this type of layered thin films show a combination of two magnetoresistance effects4, viz. the spin valve magnetoresistance ("Giant Magnetoresistance", GMR), depending on the angle between the magnetization vectors of the Ni80Fe 20 layers, and anisotropic magnetoresistance (AMR), depending on the angle between current and magnetization in each permalloy layer. In this paper we present a theoretical study of the magnetoresistance of tNiFe NiFe/tcu CU/tNiFe NiFe layered thin films. We calculate the GMR and AMR as a function of the thickness of the NiFe layers (tNiFe) and the Cu interlayer (tcu), and we will discuss the validity of a description of the combined effect in terms of a simple summation of the GMR and AMR, as proposed by Miller et al.5:

~1 R(qp, ,q 2) = Ro -'ARAMR(sin 2

•+21A~M(-O~~-)) 2

(p +

2P) +IARGMR

2

1 -cosp-p 2 ))

In this equation ip,and Tp 2 are the angles of the magnetizations of the two NiFe layers with respect to the current direction and R0 is the resistance for (p= 1 p2 =0°. Fig. 1 shows the geometry of the system. Magnetizations and current are directed Mat. Res. Soc. Symp. Proc. Vol. 313. c,1993 Materials Research Society

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in the plane of the layers. The magnetization vector of the lower NiFe(1) layer can be rotated with respect to the top NiFe(2) layer magnetization, as in the case of exchange biased systems, enabling one to create a transition between a parallel and antiparallel arrangement of the two layers, yielding the GMR. In our calculation of the AMR the current direction is rotated with respect to the direction of the magnetization of both magnetic layers, contrary to the experiments of Miller et al. 5. Figure 1: Geometry of the sample. and n1 are the NiFe magnetization vectors and It is the current.

NiFe uCC NiFe