Large Magnetoresistance Variation of Pseudo Spin Valves with Different Nano Oxide Layer Position
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Large Magnetoresistance Variation of Pseudo Spin Valves with Different Nano Oxide Layer Position Jeong Dae Suh1, and C.A. Ross2 1 Medical Information Convergence Team, Electronics and Telecommunications Research Institute, 138 Gajeongno, Daejeon, 305-350, Korea, Republic of 2 Depart of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, 02139 ABSTRACT We have investigated the influence of the nano-oxide layer positions on giant magnetoresistance (GMR), sheet resistance, surface roughness, and coercivity of the NiFe(9 nm)/Cu(4 nm)/Co(5 nm) pseudo spin valves. Nano-oxide layer positions had a several effects on the multilayer structure that changes its magnetotransport behavior. GMR ratio varied between 2.8% and 0.15% depending on the nano-oxide layer positions within the stack. The increase of the GMR ratio was accompanied by increase in resistance change, decrease in sheet resistance, and decrease in surface roughness. These significant variations of GMR ratio was explained by the changes on the spin dependent scattering or current shunting effect. Our results showed that appropriate placement of a nano-oxide layer was essential for optimizing the magnetic properties of spin valves.
INTRODUCTION Spin valve sensors are used in a variety of spintronic devices as read head sensors, magnetic memory, and magnetic biosensors [1-3]. Recently, nano-oxide layer (NOL) insertion in spin valves has been intensively studied to improve the GMR ratios, an effect that is attributed to enhanced specular reflection of electrons at the insulator/metal interfaces. The beneficial effects of oxide layers within spin valves have been demonstrated by using an oxide layer as an antiferromagnetic pinning layer [4,5], by growing an ultra-thin oxide within the multilayer or at the surface of the multilayer [6 - 15], or by using an oxide as a barrier in a current-perpendicularto-plane structure [16]. Recently, spin valve structures were reported in which the NOL insertion position was varied systematically [17-18], including placing the NOL at the midpoint of the metal layers, and at positions within the soft layer. However, the influence of NOL insertion at other positions within each layer in a spin valve has not been studied. In this article, we report the effect of NOL position on magnetic properties and GMR in the NiFe(9 nm)/Cu(4 nm)/Co(5 nm) pseudo spin valves. NOLs were prepared by natural oxidation. The films differ only in the location of the NOL, which varies in increments of 1 nm throughout the structure. The NiFe/Cu/Co/Cu structure provides a simple model for understanding NOL effects in a spin valve.
EXPERIMENT Films with structure NiFe(9 nm)/Cu(4 nm)/Co(5 nm)/Cu(2 nm) were deposited onto thermally oxidized Si (100) substrates by rf magnetron sputtering at a power of 100 W from 2
inch diameter targets at 2 mTorr argon pressure, in a system with a base pressure below 10-9 Torr. Here, NiFe represents an alloy of 80 at% Ni. A NOL was formed by natural oxidati
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