AVS 50th International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NS-TuM

Paper MI+NS-TuM6
A Practical Guide to the Interpretation of Point-contact Andreev Reflection Data

Tuesday, November 4, 2003, 10:00 am, Room 316

Session: Magnetic Imaging and Magnetic Spectroscopies
Presenter: R.J. Soulen, Naval Research Laboratory
Authors: R.J. Soulen, Naval Research Laboratory
G.W. Woods, Naval Research Laboratory
I. Mazin, Naval Research Laboratory
M. Osofsky, Naval Research Laboratory
Correspondent: Click to Email
Point-contact Andreev reflection (PCAR), has become a useful tool in determining the spin polarization, P, of magnetic materials. It consists of establishing a point contact between a sharpened superconductive point and a magnetic base (or, vice versa), and measuring the conductance G of the junction as a function of the applied voltage, V. The value of P can be extracted from the conductance data through use of a modified Blonder, Tinkham, Klapwijk (BTK) model of the supercurrent conversion at the superconductor-metal interface (Andreev reflection). This algorithm, however, does not take into account several factors which depend on properties of the point contact: whether it is in the ballistic or diffuse regime, ratio of the spreading resistance to the junction resistance, the value of the superconducting energy gap. These properties are often difficult to measure or estimate so that the practitioner is left without a means to assess the error in the value of P. We have systematically examined these effects (by theory and experiment) and can offer some new and practical guidance on how to correct for them and to estimate the error. We use data on several materials (CrO2, SrRuO, and LaSrMnO ) taken in our laboratory and in others to illustrate the process.