Magnetic and structural properties of vapor-deposited Fe-Co alloy particles

Abstract

The structural and magnetic properties of two Fe-Co alloy particles with composition Fe100−xCox(x=45,65) were studied using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. The particles were nearly spherical in shape with an average particle size around 350 Å. Particles formed long chains and showed a core/shell particle morphology. X-ray diffraction and Mössbauer studies showed the presence of bcc α-Fe-Co and CoFe2O4 phases with the former as the majority phase in Fe55Co45 and the latter the majority phase in Fe35Co65. The room-temperature coercivities of both of these samples were much higher than those in Fe particles with values exceeding 2.2 kOe. The Fe35Co65 sample showed a drastic temperature dependence of coercivity from 1.5 kOe at 300 K to 15 kOe at 10 K. The structural and magnetic data suggest a core/shell morphology with the surface oxide layer having a very important impact on both the magnitude and temperature dependence of the coercivity of the whole particle.