Electrical transport in amorphous nanofilms embedded with crystalline grains at low temperatures

Amorphous and ferromagnetic Al-Ni nanofilms have been grown by the magnetron-sputtering method with some nanosized crystalline grains embedded therein. Resistivity is demonstrated to transit from a positive temperature coefficient to a negative temperature coefficient (NTC) with increasing the fraction of Ni atoms in the Al-Ni nanofilms. The lattice disorder is deduced to induce the Anderson localization of electrons and the formation of polarons so that the NTC of the resistivity is driven in the Al-Ni nanofilms, different from that in the elemental Al and Ni nanofilms. The electron transport in the Al-Ni nanofilms is dominated by polaron hopping while it is also determined by electron-magnon and electron-phonon scatterings. The electron-magnon scatterings are further revealed to have a more important contribution to the electron transport at low temperatures than electron-phonon scatterings in the amorphous Al-Ni nanofilms. A so-called polaron-metal physical model has thus been proposed to well explain the electron transport in disorder lattices with crystalline grains embedded therein. This study may help to optimize the design of nano-engineered devices.