The structural, magnetic and nanomechanical properties of hexagonal Co thin films

Ferromagnetic (FM) Co thin film can provide a free and/or pinned layer in the magnetic tunnel junction (MTJ). Because the mechanical and microstructure properties of Co are crucial to device performance in read head, gauge sensor, and magnetoresistance random access memory (MRAM) applications, it is worthwhile to study the strength and durability of the device. However, few researchers have studied these properties at room temperature (RT) and in heat-annealing environments. In this work, Co thin films were sputtered onto the glass substrates with the thickness (tf) varied from 100 Å to 500 Å under different conditions: (a) the substrate temperature (Ts) kept at RT and (b) Ts = RT and post-annealing heat treatments. The hardness and Young's modulus of the Co thin films were obtained from nanoindentation tests. To observe the grain distribution, we observed the plane-view microstructure with high-resolution transmission electron microscopy (HRTEM). From the electron diffraction pattern, we found that the Co thin film had a hexagonal (HCP) structure. Based on the nanoindentation results, the mechanical properties of Co thin films are an interesting issue in the magnetic industry applications.