Reduced magnetic coercivity and switching field in NiFeCuMo/Ru/NiFeCuMo synthetic-ferrimagnetic nanodots

The coercivity (Hc) and switching field (Hsw) of free layers increase remarkably with shrinking structural dimensions, reducing the sensitivity of nanosized magnetoresistive sensors. In this work, conetic-alloy (NiFeCuMo) synthetic ferrimagnetic (SyF) trilayers are proposed to reduce Hc and Hsw in magnetic nanostructures. SyF stacks of NiFeCuMo/Ru/NiFeCuMo were patterned into nanodot arrays with diameter of 60 nm by nanosphere lithography. The thickness of Ru layer was chosen so that high interlayer coupling energy existed in the continuous film. The linear dependence of Hc and Hsw of SyF nanodot on the amplification factor was revealed. Magnetic field annealing was conducted at various temperatures (Tan) ranging from 373 K to 673 K. Annealing at low temperature (Tan ≤ 473 K) relaxed the structural disorders, resulting in reduced surface roughness and decreased Hc and Hsw. Higher Tan changed the preferred orientations in the crystalline structures, leading to increased roughness and higher Hc and Hsw. This work shows that the Hc and Hsw of nanostructures can be reduced through engaging Conetic alloy in SyF stack. The Conetic-alloy-based SyF structures are a promising candidate as free layers in nanosized spintronic devices.