Size effect and temperature dependence of spin conduction in Gd/SiN ultrathin film

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 susceptibility χ at T_C is almost unchanged as in epitaxial Gd on metal. The resistivity R doubled as the Gd layer thickness decreases from 100 to 10 nm, and the T_C estimated from R agrees with that from χ. Additionally, a possible interlayer coupling or an effect of surface layers adjacent to Si₃N₄ was detected in superlattices.