Structure, stress, and magnetic properties of high saturation magnetization films of FeCo

Thin (∼2000 Å) films of Fe₆₀Co₄₀ have been prepared by sputtering on Si/SiO₂, Si/AlO_x, AlTiC/AlO_x, AlTiC/AlO_x/NiFe, and AlTiC/AlO_x/NiFeCr substrates using an alloy Fe₆₀Co₄₀ target. The structure of the films was characterized by means of X-ray diffraction and transmission electron microscopy (TEM). Surface roughness was characterized by atomic force microscopy (AFM). Stress, transport, and magnetic measurements were conducted. We observed correlation in the following pairs of properties: coercivity-stress, grain size-stress, and coercivity-grain size. Although individual films had a stress in the wide range of compressive 2.5×10¹⁰ Dyne/cm² to tensile 1.3×10¹⁰ Dyne/cm², which depended to some degree on the material of the substrate and underlayer, we found that biaxial stress and coercivity seem to be described by a general trend, with coercivity being as low as 19 Oe at intermediate tensile stress and as high as 225 Oe at high compressive stress. The unstrained lattice parameter and Young´s modulus of the alloy Fe₆₀Co₄₀ were also determined.