Atomic-scale modification of hybrid FePt cluster-assembled films

Abstract

We present a study on the production of iron-platinum bimetallic clusters with a laser vaporization cluster source, and subsequent low-energy cluster beam deposition in ultrahigh-vacuum conditions. Time-of-flight mass spectrometry investigations of the clusters in the gas phase show that FePt is a stable alloy at the nanoscale. Magnetic and structural properties of the deposited $2.25\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ cluster-assembled films with different Fe:Pt ratios are investigated with vibrating sample and superconducting quantum interference device magnetometry, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction. The as-deposited cluster films are highly porous and magnetically soft. A systematic study of the influence of annealing on the sample properties revealed that the chemically disordered-ordered phase transition only occurs in the cluster films with Fe:Pt ratio close to 1:1, and at temperatures higher than $500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Combining magnetization and structural investigations we distinguish between the phase transition inside a single cluster and the coalescence of clusters, which starts to dominate at temperatures above $550\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, leading to complete cluster intermixing on the atomic level.