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

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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.