The possibility of enhancing the resistivity while preserving magnetism is
investigated by growing metal/insulator trilayers and superlattices, where
the metal is Gd and the insulator is amorphous Si3N4 for the first time. A
large size effect on Curie temperature (T-C) is found in the susceptibility
in contrast with Gd epitaxially grown on metals. T-C decreases to 180 K, i
.e., 70% of the bulk T-C in 10 nm thick Gd film, which is attributed to an
electrical isolation and surface states. On the other hand, the susceptibil
ity chi at T-C is almost unchanged as in epitaxial Gd on metal. The resisti
vity R doubled as the Gd layer thickness decreases from 100 to 10 nm, and t
he T-C estimated from R agrees with that from chi. Additionally, a possible
interlayer coupling or an effect of surface layers adjacent to Si3N4 was d
etected in superlattices. (C) 2000 American Institute of Physics. [S0021-89
79(00)86808-5].