Critical behaviour of nanocrystalline gadolinium

For single crystalline gadolinium (Gd), Srinath, Kaul, and Kronmueller have demonstrated that Gd belongs to the uniaxial dipolar universality class with a Curie temperature Tc=292.77 K. For polycrystalline Gd, the critical behaviour seems to be strongly affected by the microstructure when the crystallite size D is reduced to the nanometer regime. The most striking feature in this context is the continuous reduction of Tc with decreasing D which yields Tc-shifts of 10 K and more for grain sizes below 30 nm. Here, we report on the critical behaviour of inert-gas condensed nanocrystalline Gd (with 8 nm<D< 21 nm) which has been studied by means of ac-susceptibility and small-angle neutron scattering.