The growth of metastable fcc Fe₇₈Ni₂₂ thin films on H-Si(100) substrates suitable for focused ion beam direct magnetic patterning

Abstract

We have studied the growth of metastable face-centered-cubic, non-magnetic Fe78Ni22 thin films on silicon substrates. These films undergo a magnetic (paramagnetic to ferromagnetic) and structural (fcc to bcc) phase transformation upon ion beam irradiation and thus can serve as a material for direct writing of magnetic nanostructures by the focused ion beam. So far, these films were prepared only on single-crystal Cu(1 0 0) substrates. We show that transformable Fe78Ni22 thin films can also be prepared on a hydrogen-terminated Si(1 0 0) with a 130-nm-thick Cu(1 0 0) buffer layer. The H-Si(1 0 0) substrates can be prepared by hydrofluoric acid etching or by annealing at 1200 °C followed by adsorption of atomic hydrogen. The Cu(1 0 0) buffer layer and Fe78Ni22 fcc metastable thin film were deposited by thermal evaporation in ultra-high vacuum. The films were consequently transformed in-situ by 4 keV Ar+ ion irradiation and ex-situ by a 30 keV Ga+ focused ion beam, and their magnetic properties were studied by magneto-optical Kerr effect magnetometry. The substitution of expensive copper single crystal substrate by standard silicon wafers dramatically expands application possibilities of metastable paramagnetic thin films for focused-ion-beam direct magnetic patterning.