Magnetoresistance Measurements on Boron-Doped and Undoped Ni 3 Al Thin Films
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Magnetoresistance Measurements on Boron-Doped and Undoped Ni3Al Thin Films Edward C. Patterson, Jr. and L. L. Henry* Department of Physics, Southern University and A. & M. College, Baton Rouge, LA 70813, U.S.A. *Corresponding author. ABSTRACT Magnetoresistance measurements were performed in magnetic fields up to 5 T, to examine the effects of boron doping on the electron transport properties of Ni3Al thin (500 Å, nominal, thickness) films. Both a doped (~200 ppm B) and undoped film were investigated. Four-probe magnetoresistance (magnetic field = 50 G and 5 T) measurements indicate that both samples undergo a phase transition in the 200 K – 300 K temperature range.
INTRODUCTION Nickel aluminide in the thin film form possesses superior qualities in regards to surface strength, corrosion and resistance to oxidation, compared to the bulk. Consequently, the thin film form provides possibilities for use in miniaturized systems such as microelectromechanical systems (MEMS) and devices [1-3]. For these applications the effect of an applied magnetic field on the electrical resistance should be beneficial. Electrical resistance properties have been investigated for the bulk form [4], but the thin film form has not been as thoroughly studied. This paper presents results of magnetoresistance measurements performed on thin films of Ni3Al, and also the effect that doping the material with boron atoms has on it.
EXPERIMENTAL DETAILS The samples were fabricated using an ion beam sputtering technique applied to: (i) a compound target containing Ni3Al with boron doping to a concentration of approximately 200 ppm. of boron, and (ii) a pure Ni3Al target. Two samples were fabricated, one of pure Ni3Al, and the other of boron doped Ni3Al (i.e., ~200 ppm B). Both samples, 500 QRPLQDO WKLFNQHVV each, were sputtered onto the polished sides of silicon substrates that had dimensions of approximately 1cm x 1 cm x 0.5 mm. Magnetoresistance (MR) measurements were performed at 50 G as the temperature was decreased by 5 K intervals from above 300 K to 5 K, then the temperature was raised to above 300 K again and the measurement repeated with the magnetic field set to 5 T. The MR measurements were made using a four-probe current-voltage method and “van der Pauw”[5] geometry, with the samples located in the sample space of the solenoid of a Quantum Design MPMS-5S magnetometer system. The applied magnetic field is oriented parallel to the plane of the film. The samples had to be cut to rectangular shape with dimensions of approximately 1 cm x 0.5 cm, to fit into the sample space. For the MR measurements the voltage and current leads were attached to the corners of the samples using indium and silver paint. The lead connections to the sample and the orientation of the sample with respect to the magnetic field were made as shown in Figure 1. P3.24.1
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(a) (b) Figure 1. The resistance measurement geometry, rela
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