New methods to measure the current perpendicular to the plane magnetoresistance of multilayers

Abstract

The experimental devices presented here enable us to measure variations with magnetic field of electrical resistances in the range (0.1 nΩ, 1 μΩ), for applied magnetic fields up to 3 T, and for temperatures 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 pΩ, and their relative resolution ΔR/R is limited to 0.3%. The third method is a sinusoidal field modulation technique giving the field derivative of the resistance: dR/dH. It is sensitive to variations of the resistance as small as 1 pΩ independent of the absolute resistance of the sample, thus the resulting resolution ΔR/R is, for example, 10−6 for a 1 μΩ sample. With these devices, the magnetoresistance of multilayers can be studied with the current perpendicular to the plane.