Surface properties of an itinerant paramagnet

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Abstract
We calculate within a simple model of an itinerant paramagnet the magnetization response to a uniform static field and, for an ad-spin near the surface, the second-order binding energy and Brownian-motion friction parameter. We use the random-phase approximation to treat the exchange enhancement of the paramagnet. Several approximation schemes are explored for solving the basic integral equation. The friction parameter is notably sensitive to the choice of approximation, but we can conclude that, for an exchange interaction of reasonable range and strength, it shows no special behavior in the surface region. We also apply our formulas to examine the friction parameter of an ion near a metal surface, finding significant modification of previous calculations.