Phase transformation of (Ni66Fe22Co12)(x)C1-x nanocomposite films preparedby d.c. magnetron co-sputtering

(Ni66Fe22Co12)(x)C1-x nanocomposite films with x = 10-75 at.% were prepared by d.c. magnetron co-sputtering. Subsequent thermal annealing was performe d in a vacuum (<2X10(-3) Pa) furnace for 1 h at various temperatures. The m icrostructure evolution of the as-deposited and annealed films was characte rized by non-Rutherford backscattering spectroscopy, X-ray photoelectron sp ectroscopy, X-ray diffraction, Raman spectroscopy, and atomic force microsc opy. Results showed that the phase transition with the increase of annealin g temperature was closely dependent on the composition. Films with less tha n 20 at.% NiFeCo showed an amorphous structure in the as-deposited and up t o 400<degrees>C annealed samples. After annealing at 500 degreesC, a small amount of face-centered-cubic (fcc) crystalline NiFeCo precipitated while c arbon remained amorphous. For the films with NiFeCo concentration in the ra nge of 30-55 at.%, the as-deposited films were found to consist of very sma ll NiFeCo nanocrystals encapsulated in amorphous carbon. After annealing, t he crystal grain size of the alloys increased with the increase of annealin g temperature while carbon was graphitized. For the films with more than 62 at.% NiFeCo, the as-deposited films went through a meta-stable stage at wh ich a rhombohedral Ni3C phase and fee NiFeCo co-existed upon annealing to a temperature between approximately 300 and 400 degreesC (dependent on compo sition). Upon further annealing to a sufficiently high temperature between approximately 350 and 500 degreesC, the carbide phase decomposed and only t he fee NiFeCo nanocrystals encapsulated in graphite existed in the films. ( C) 2001 Elsevier Science B.V. All rights reserved.