Study of exchange anisotropy for Ni80Fe20/Fe60Mn40 (111) epitaxial films

Abstract

Ni 80 Fe 20 / Fe 60 Mn 40 (111) epitaxial films grown on Si(110) buffered by Cu were studied systematically by varying the individual layer thicknesses with emphasis on the detailed structure evolution and its influence on the magnetic properties. The Cu buffer layer induced epitaxial face-centered-cubic (111) growth. Film crystallinity improved as the Cu buffer layer thickness t increased, evidenced from the full width of half maximum of 3.3° for t=1 nm and 1.1° for t=100 nm. Film surface roughness increased from 0.56 to 1.1 nm with increasing Cu buffer layer thickness. The exchange bias field was around 90 Oe when the Cu buffer layer film thickness was less than 10 nm, higher than the 70 Oe for films with thicker Cu buffer layers. Reversible measurements of the exchange coupling strength were ∼70 Oe larger than the loop shift for films with Cu buffer layer thickness greater than 10 nm. For these films the coercivity was larger than 30 Oe. A magnetic force microscope showed a magnetization ripple pattern with a characteristic length of ∼2 μm, indicating a strong stray field. The angular dependence of exchange bias field for epitaxial films was quite different from that of polycrystalline films.