Carbonization behavior of polyimide film containing iron complex in relation to magnetic properties

Abstract

A ferromagnetic film composed of carbon matrix and dispersed fine iron particles was prepared by heating a polyimide film containing iron complex at temperatures up to 1000 °C. The particles were formed and distributed homogeneously on the film surfaces by heat treatments at 600 °C and above, and inside the films at 700 °C and above. The particles were α–Fe, γ–Fe (or austenite), and Fe3C with fractions of about 7:2:1 in the films heated at 800 °C and above. The mean crystallite sizes of α–Fe and γ–Fe (or austenite) particles were evaluated to be 19 and 15 nm in the film heated at 800 °C, and 32 and 30 nm at 1000 °C, respectively. The films heated at 600 °C and below were superparamagnetic, while those at 700 °C and above were ferromagnetic, but both components existed in all films. The iron particles promoted the growth of carbon crystallites in the films; i.e., the interlayer spacing was about 0.341–0.343 nm and mean crystallite size 4.0–6.5 nm for the films heated in the range of 700 to 1000 °C. Pores were observed on the surfaces and cross sections of the carbonized films, and they seemed to be loopholes of the clusters. Iron oxides were scarcely formed in the films, even after being kept for a long duration at room temperature in atmosphere.