Universal mB/T Scaling of the Giant Magnetoresistance in Cu-Co Granular Ribbons Produced by Controlled Melt-Spinning
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INTRODUCTION Ever since the discovery of giant magnetoresistance, GMR, in granular solids containing transition metal elements in a non magnetic metallic matrix', there has been extensive efforts both from an experimental as well as theoretical point of view. The above phenomenon has also been observed in melt-spun ribbons made of similar constituents2 . GMR in granular solids appears to be concomitant with a superparamagnetic has been given by Parker et al. 6 in terms of behaviour3' 5 . An attempt for such a correlation Langevin function. It has also been shown"'8 that AR scales with BIT. GMR has also been 5 . Such correlation has been correlated with the square of the macroscopic magnetization"' explained in terms of a spin dependent scattering model 9. GMR in granular solids has also been explained by considering interfacial spin dependent scattering of conduction electrons, using a lognormal distribution function for the cluster size'°. Also, in some studies GMR has been shown to depend linearly, and not as the square of the magnetization, which is considered to arise from scattering of pairs of blocked and superparamagnetic particles". In the present work, we show a correlation between the magnetic nature of the samples and their GMR, taking into account their dependence on magnetic field and temperature, as well as the modifications which takes place with annealing treatments. The magnetization behaviour is described by a Langevin function. We analyse our data by considering a spin dependent scattering model, and the dependence of GMR to the square of the magnetization. From such an analyses we find that GMR scales with mB/T and thereby the role of number and size of magnetic clusters in describing the temperature dependence of GMR. EXPERIMENTAL Controlled inert atmosphere melt-spinning technique has been used to produce Cu 92Co 8 and Cu, 6Co,4 ribbons 30 gm thick and 2.5 mm wide. We have annealed in inert atmosphere samples in a commercial halogen lamps furnace as follow: 500 'C for 60 min., 600 'C for 30 min. and 700 cC for 30 min. X-ray diffraction using Cu-Ka radiation (Q=1.5423A) as well as 200 kV transmission electron microscopy (TEM) investigation have been carried out in commercial equipment's. Details of these analyses have been reported before8 . 541
Mat. Res. Soc. Symp. Proc. Vol. 384 01995 Materials Research Society
MR measurements in Cu 9 2Co 8 have been made using the four probe technique with 1 mA d.c. flowing along the ribbon. The field was applied parallel to the current. The voltage drop was measured over a length of 6.5 mm, from which the resistance can be obtained. The SQUID was used to provide the field and the low temperature capability. Cu 86Co 14 samples have been annealed in a conventional resistance furnace at 425 'C, 450 'C, 475°C, 500 'C and 600 °C for I h. in inert atmosphere. MR measurements have been made by means of an Automatic Resistance Bridge from A.S.L. model F26. 1 mA current was flowing along the ribbon 12 mm. long, 1 mm width, and the magne
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