Mössbauer effect of dilute Fe in sputtered Co-Cr films

Abstract

Mössbauer effect measurements have been obtained on sputtered Co–Cr films containing a small amount of iron, with compositions Co76Cr20Fe4. Two features are observed: a single line (about 25% of the spectral area) and a broadened, magnetically split spectrum. From the isomer shift and lack of magnetic splitting in the former, the nonmagnetic phase in sputtered Co–Cr alloys is identified as being nearly pure Cr. In particular, the nonmagnetic phase can contain less than a few percent of the initial Co concentration. The magnetic phase has a decreased average magnetic hyperfine field relative to Fe in Co, and an isomer shift consistent with a Cr concentration about one-half that of the initial Cr concentration. A substantial perpendicular polarization of the Fe moments is seen, although magnetic data indicate an easy plane orientation. The phase segregation in Co–Cr films is shown to be similar to the ‘‘475 °C embrittlement’’ long known in Fe–Cr alloys, and to the segregation that occurs in ductile Fe–Co–Cr–Si permanent magnets.