Optical, structural, and magnetic properties of cobalt nanostructure thin films

We report on optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85° away from the substrate normal. Comparison is made between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation. Generalized spectroscopic ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the films in the spectral range from 400 to 1000 nm. The magnetic properties are analyzed with a superconducting quantum interference device magnetometer. Both nanostructure thin films show highly anisotropic optical properties such as strong form birefringence and large dichroism. In particular, Co slanted columnar thin films are found to possess monoclinic optical properties. Magnetic measurements at room temperature show hysteresis anisotropy with respect to a magnetic field either parallel or perpendicular to the nanostructures' long axis. We find extremely large coercive fields of approximately 3 kOe for our achiral columnar nanostructures.