The precipitation behavior of nano‐scale Co particles formed in a Cu–Co alloy was studied by means of transmission electron microscopy and a Monte‐Carlo simulation. Small coherent Co particles were randomly formed at the early stage of the precipitation process. Two or more Co precipitates linked together were linearly arranged to the 〈100〉 orientation of the copper matrix, at the later stage of the coherent precipitation. Finally, the particles lost their coherency to the Cu matrix, and incoherent Co precipitates appeared. The Monte‐Carlo simulation, which took both chemical and magnetic interactions into account, strongly suggested that the coupling of coherent Co particles was realized as a result of the chemical and magnetic interactions between the Co particles, which are adjacent to each other.

We propose and demonstrate a novel biosensor based on a silicon-single-microring-resonator-loaded Mach-Zehnder interferometer (MRR-MZI), and discuss the design of the sensor theoretically. Owing to the combination of an MZI and the enhanced phase change in a microring resonator (MRR), high sensitivity is expected to be realized. The designed MRR-MZI sensor is fabricated using a CMOS-compatible process, and its sensing characteristics are measured using ethanol solutions with a concentration of less than 3 wt % and avidin solutions. The sensitivity of the MRR-MZI to changes in the environmental refractive index is increased by approximately 50 times compared with that of a simple MRR. In addition, avidin solution with a concentration as low as 20 pM was successfully detected.