Patent ID: 8027185

Claim:
A method for determining variables that characterize a tunnel junction film stack, comprising: estimating a plurality of variables defining theoretical data in order to fit the theoretical data to a plurality of measured data, the measured data comprising measured resistances determined from measuring resistances at a plurality of spacings of probes electrically coupled to a surface of a tunnel junction film stack; and adjusting the plurality of variables until the theoretical data fit the measured data within a predetermined error, wherein the theoretical and measured data are fit by using at least the following formula: R = R F || R P 2 ⁢ ⁢ π ⁢ { R F R P ⁡ [ K 0 ⁡ ( a λ ) + K 0 ⁡ ( d λ ) - K 0 ⁡ ( b λ ) - K 0 ⁡ ( c λ ) ] + ln ⁡ [ bc ad ] } , where a corresponds to spacing between an I + probe and an V + probe, b corresponds to spacing between the I + probe and a V − probe, c corresponds to spacing between the V + probe and an I − probe, d corresponds to spacing between the V − probe and the I − probe, R F is a resistance per square of a free layer in the tunnel junction film stack, R P is a resistance per square of a pinned layer in the tunnel junction film stack, R F ∥R P =R F R P /(R F +R P ), R is a resistance, λ is a length scale, and K 0 is a modified Bessel function of the second kind of order zero, wherein one or more of the estimating step or the adjusting step are performed by one or more hardware devices.