Dimensional-crossover studies of magnetic susceptibility in diluted-magnetic-semiconductor superlattices

A planar dc SQUID with integrated pickup loops and field coils has allowed precise ac magnetic susceptibility measurements of ${\mathrm{Cd}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{x}}$Te-CdTe superlattices as a function of temperature and applied magnetic field. The spin-glass transition in 86-Å-thick magnetic layers broadens and disappears as the thickness is reduced to 18 Å, suggesting the inability of the 2D system to support long-range spin-glass order. Novel hysteretic effects are seen in the thinnest layers.