Magnetic Properties of Nanostructured Fe/Ag Composite Metal Films
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MAGNETIC PROPERTIES OF NANOSTRUCTURED FE/AG COMPOSITE METAL FILMS
S.H. Liou, Y.X. Zhang, R.J. DeAngelis
Center for Materials Research and Analysis, University of Nebraska-Lincoln, Lincoln, NE 68588-0111
ABSTRACT We have synthesized a series of nanostructured Fe/Ag composite metal films. The much enhanced magnetic coercivity was found to scale with the particle size which is process controlled. At a low substrate temperature(< 2000C), the film consists of small clusters of Fe(< 100A) which behave superparamagnetically with a blocking temperature above 100K. INTRODUCTION The nanostructured composite material can be formed by the mixing of two immiscible constituents. The constituents can be a combination of metal and insulator, which is generally referred to as a granular metal, or metal and metal, which is generally referred to as a precipitated alloy. These two types of alloys are quite similar because both consist of small nanometer-size particles embedded in a matrix. The persistent interest in granular metal films is due primarily to their unusual transport, optical, superconducting and magnetic properties [1-5]. It has been shown that the magnetic properties of granular solids axe determined by the intrinsic properties and volume fraction of metal, as well as the granule size [6]. The main features of the magnetic behavior of granular films are the presence of ferromagnetic-superparamagnetic transition and high magnetic coercivity. We have demonstrated that these magnetic properties are mainly affected by the particle size distribution in the films [5,6]. In this paper, we investigate the magnetic properties of Fe/Ag composite materials. In particular, we report on the control of the particle size via a sputtering process* condition and on their magnetic properties which are functions of particle sizes. Experimental Procedure The Fe/Ag composite metal films were prepared by DC magnetron sputtering using a single composite metal target. The sputtering target was made by sintering a mixture of Fe and Ag powders with a atomic ratio of 55:45. The sputtering gas was 4 mtorr of Ar. The substrate temperature varied from 100'C to 500 0 C. The film thickness was about 2/Am. The structure of the films was investigated using a Regaku x-ray diffractometer with a Cu target. The magnetizatin and coercive force were measured by a Vibrating Sample Magnetometer(VSM). In our sputtering configuration, the substrates were 5 cm. above the magnetron sputtering gun, so they were experiencing a small magnetic field (about 100 G normal to the film surface). Mat. Res. Soc. Symp. Proc. Vol. 195. 01990 Materials Research Society
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We found that the composition of the thin-film deposit was not the same as the composition of the powder mixture in the sputtering target. Compositions were quantitatively determined by using energy dispersive x-ray analysis in a scanning electron microscope. However, the compositions of the films from each run were very consistent. The variation of iron concentration was within 3 atomic %. In this study
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