Magnetic transport mechanism in double ferromagnetic tunnel junctions with two-dimensional ferromagnetic particles

Magnetic transport properties of Co₉₀Fe₁₀/AlO_x/Co₉₀Fe₁₀/AlO_x/Co₉₀Fe₁₀ ferromagnetic double tunnel junctions have been investigated with respect to the thermal fluctuation. A middle Co₉₀Fe₁₀ layer is discontinuous by forming Co₉₀Fe₁₀ particles two-dimensionally, which shows superparamagnetic behavior above 80 K. The average diameter of the Co₉₀Fe₁₀ particles is estimated to be 4.8-5.0 nm from both a magnetization curve at room temperature and temperature dependence of coercivities deduced from magnetoresistance curves. This finding agrees with the maximum diameter (5.2 nm) evaluated from cross-sectional transmission electron microscope images, revealing that the dominant electron transport process heavily depends on the largest particles.