NEW METHODS TO MEASURE THE CURRENT PERPENDICULAR TO THE PLANE MAGNETORESISTANCE OF MULTILAYERS

The experimental devices presented here enable us to measure variation s with magnetic field of electrical resistances in the range (0.1 n Om ega, 1 mu Omega), for applied magnetic fields up to 3 T, and for tempe ratures less than 9 K. The setups work with three measurement methods. Two provide direct access to R(H), one in constant current, the other in alternating current. Their absolute sensitivity is about 1 p Omega , and their relative resolution Delta R/R is limited to 0.3%. The thir d method is a sinusoidal field modulation technique giving the field d erivative of the resistance: dR/dH. It is sensitive to variations of t he resistance as small as 1 p Omega independent of the absolute resist ance of the sample, thus the resulting resolution Delta R/R is, for ex ample, 10(-6) for a 1 mu Omega sample. With these devices, the magneto resistance of multilayers can be studied with the current perpendicula r to the plane. (C) 1996 American Institute of Physics.