MAGNETIC-COHERENCE-LENGTH SCALING IN METALLIC MULTILAYERS - COMMENT

In a recent paper [Phys. Rev. B 54, 515 (1996)], Koperdraad and Lodder compare calculations of the parallel critical field H-c2(\\), in supe rconductor-normal-metal multilayers with experimental data taken from the literature. The poor agreement leads them to introduce a scaling f actor alpha in the superconducting coherence length. The aim of this C omment is to point out the importance of the boundary conditions of th e problem. Free sample surfaces will yield different results than an i nfinite stack of layers. The effect of free surfaces on the temperatur e of the dimensional crossover in H-c2(\\) is shown to be similar to t he effect of alpha, making the need for the latter parameter questiona ble.