Logarithmic Relaxation of Resistance in Time of Annealed and Plastically Deformed Au 80 Fe 20
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Logarithmic Relaxation of Resistance in Time of Annealed and Plastically Deformed Au80Fe20 P.Allia1, M.Baricco2, E. Bosco2, M.Coisson1, D. Falletti2, V. Selvaggini1, P.Tiberto3, F.Vinai3 1
DIFIS-DISPEA, Politecnico di Torino and INFM, Corso Duca degli Abruzzi 24, I-10129 Torino, Italy 2 IFM, Università di Torino and INFM, Via Pietro Giuria 7, I-10125 Torino, Italy 3 IEN Galileo Ferraris and INFM, Corso M. d'Azeglio 42, I-10125 Torino, Italy
ABSTRACT Rapidly solidified Au80Fe20 ribbons were prepared either by melt spinning or by solidstate quenching of a homogenised master alloy. The as-quenched sample displays a paramagnetic behavior indicating a perfect solid solution of Fe in the Au matrix. Subsequent anneals have been performed to induce the precipitation of Fe particles. X-ray diffraction technique have been exploited to determine the alloy microstructure. The structural stability have been studied by measuring electrical properties in isothermal and tempering condition. The variation of magnetisation and electrical resistance have been measured after submitting the samples to plastic deformation. A logarithmic relaxation of the electrical resistance is observed in all studied samples after deformation. Magnetic hysteresis loops have been measured in as-quenched and annealed samples at different temperatures. X-ray diffraction and magnetic measurements indicate that thermal treatments have been successful in inducing the precipitation of both bcc and fcc Fe clusters.
INTRODUCTION
The Au100-xFex magnetic system has been thoroughly studied since many decades owing to its notable magnetic properties at low and high temperature, including magnetic cluster formation, mictomagnetism, superparamagnetism, Kondo effect in various ranges of Fe concentration [1]. The AuFe alloy, usually consisting of very small Fe clusters (composed of a few adjacent Fe atoms) often associated with larger, superparamagnetic Fe particles, is known to be a spin glass [2]. These features make this alloy eligible as a system displaying giant magnetoresistance [3]. Metastable metallic alloys rapidly quenched from the melt are usually characterised by attractive physical properties [4]. Thermal treatments, acting to modify the structure and properties of Au-Fe metastable systems may lead to Fe precipitation and to a stabler configuration. The study of relaxation processes of magnetic and electrical properties, strictly connected to the intrinsic metastability of the alloy, becomes of particular relevance to gain a better knowledge of application-oriented properties. In particular, the electrical resistance in AuFe alloys has been shown to change with time after being submitted to mechanical deformation [5,6]. This peculiar behavior has been explained by offequilibrium displacement of defects/vacancies induced by plastic deformation, whose relaxation is connected to the time variation of the electrical resistance [5,6]. In this work, the microstructural and compositional stability of rapidly quenched Au80Fe20 have been studied and related to
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