Comment on “Magnetic-coherence-length scaling in metallic multilayers”

In a recent paper [Phys. Rev. B 54, 515 (1996)], Koperdraad and Lodder compare calculations of the parallel critical field H_c2^‖ in superconductor–normal-metal multilayers with experimental data taken from the literature. The poor agreement leads them to introduce a scaling factor α in the superconducting coherence length. The aim of this Comment is to point out the importance of the boundary conditions of the problem. Free sample surfaces will yield different results than an infinite stack of layers. The effect of free surfaces on the temperature of the dimensional crossover in H_c2^‖ is shown to be similar to the effect of α, making the need for the latter parameter questionable.