Elaboration of Single Crystalline AU/NI 80 FE 20 /CU/NI 80 FE 20 /NIO(111) Spin Valves
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ABSTRACT The successful preparation of fully epitaxial spin-valves elaborated on NiO(1 11) single crystals is reported. The growth conditions of a smooth 2D permalloy (Py = NisoFe 20) layer have been determined. A very strong magnetic exchange interaction is evidenced on the Py/NiO(1 11) interface. It strongly modifies the magnetic properties of Py that acquires high coercivity, leaving it as a hard magnetic material. The second Py layer has unchanged magnetic properties and plays the role of the sensing soft magnetic layer. A giant magnetoresistance (GMR) of 3.5% at room temperature was easily obtained without optimizing the thickness of the different layers. Complementarily energy-filtered (EF-) and high-resolution (HR-) transmission electron microscopy (TEM) were used to fully characterize the spin valves. Within the framework of magnetic exchange coupling, our results open the possibility to elaborate model spin valves in which the role of each interface can be investigated and controlled at the atomic level. The detrimental effect of an inter-diffusion at the Py/NiO interface is evidenced. INTRODUCTION The steadily increasing demand on storage capacity motivates the great interest for new generations of sensor devices. The spin-valve geometry stands as the current commercial replacement for inductive hard-drive read-heads [1-3]. Many studies were performed on various ferromagnetic on antiferromagnetic (F/AF) systems and different layer combinations were tested. An overview of the advantages and drawbacks of each of them can be found in [1]. One of the most promising candidate to play the AF pinning layer role in spin-valves is NiO, with the (111) spin-uncompensated polar surface [4]. Read heads based on NiO have proven to possess adequate properties during read cycles on magnetic media [1-3] because NiO is a highly corrosion resistant insulating antiferromagnet and it has a relatively high Ndel temperature (520 K). The NiO based sensors may thus be used in hard drive read-heads, permanent magnetic memories, as well as in harsh environment applications. However, the magnetic exchange-coupling phenomenon making these devices work is still not fully understood and several models were proposed. The successful existing devices were mostly optimized within an experimental trial/error method and no model structure was available up to now. This may be of particular importance since the interface regions are usually suspected to play the dominant role. In the present paper we report the elaboration of such a model spin-valve for which the crystalline structure is fully known. Moreover, the enhanced exchange coupling due to the single crystal substrate allows building the whole structure with Py. First, we recall the experimental details before showing some results, which will be discussed in the last part of the paper, after which we shall conclude.
91 Mat. Res. Soc. Symp. Proc. Vol. 619 ©2000 Materials Research Society
EXPERIMENTAL The investigation of the growth mode was performed by Grazing Incidence X-ray Diffra
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