The Microstructure and Giant Magnetoresi Stance of NiFeAg Thin Films
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THE MICROSTRUCTURE AND GIANT MAGNETORESISTANCE OF NiFeAg THIN FILMS MICHAEL A. PARKER, K. R. COFFEY, T. L. HYLTON AND J. K. HOWARD IBM, Advanced Storage and Retrieval, IBM Fellow Program, 5600 Cottle Road, San Jose, CA 95193
ABSTRACT Although much has been published on giant magnetoresistance (GMR) in co-deposited thin films [1-4], only little [5] has been published on the structure-property relationships limiting the effect. Here, we report the results of microstructural characterization of NiFeAg thin films that exhibit a GMR effect. The as-deposited films show a sizeable GMR effect. The maximum GMR effect observed was 6.4% with -4kOe FWHM of the 6p/p peak. Upon annealing these films, the GMRat first increases, and then decreases. We present microstructural evidence from TEM and XRD, amongst other techniques, which shows that this is a consequence of the initial NiFeAg thin film agglomerating into NiFe grains in a predominantly Ag segregant matrix. Upon extended annealing, excessive grain growth leads to a decrease in the GMRas predicted by the model of Berkowitz, et al. [1].
INTRODUCTION The phenomenon of giant magnetoresistance (GMR) is well established in multilayers containing antiferromagnetically coupled ferromagnetic materials separated by non-magnetic interlayers [6-8]. The phenomenon of giant magnetoresistance in granular ferromagnetic materials isolated in a non-magnetic matrix, or granular giant magnetoresistance (GGMR, G2MR), has only recently been discovered [1-4]. The structure-property relationships in these materials is just beginning to be understood [5]. To gain insight into the mechanisms underlying this effect, we compared the unannealed microstructure of a NiFeAg thin film and that of samples annealed at 3001C, 3501C, and 4001C for 10 min each with the accompanying changes in the G2 MR.
EXPERIMENTAL DETAILS The samples were produced in a Sputtered Films Incorporated (SFI) S-gun magnetron sputtering system by codeposition from a pure Ag and a Ni 8 1 Fe, 9 target so that the films were -75% by volume Ag, the remainder Ni,,Fe1 9 . The films were nominally 300A thick. They were annealed by rapid thermal processing in an AG Heatpulse model 610 system for 10 min at 3001C, 350 0 C, and 400*C, respectively. The magnetoresistance was measured in a Digital Measurement Systems VSM equipped with a four point probe for measuring resistance changes. GMR measurements were performed at room temperature. The microstructural changes in the samples were characterized by x-ray diffraction (XRD) analysis on the Rigaku DMAX-1O00 system using the conventional Bragg-Brentano reflection geometry, and at a grazing incidence angle of 50 whilst scanning 28. Through foil (TF) transmission electron microscopy (TEM) was performed on the samples using the JEOL 4000FX analytical TEM. The samples were prepared for microscopy by lapping them Mat. Res. Soc. Symp. Proc. Vol. 313. 01993 Materials Research Society
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until they became transparent to the transmission of light, which is somewhat less than 5 p in thickness. Fin
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