A method of forming an inductor assembly includes depositing a magnetic core on a planar substrate lying in a core plane, forming an inductor coil that generates a magnetic field that passes through the magnetic core in a closed loop parallel to the core plane, and annealing the magnetic core while applying an external magnetic field that passes through the magnetic core in a radial direction to permanently fix the easy axis of magnetization parallel to the radial direction. As a result, the hard axis of magnetization of the magnetic core is permanently oriented in a generally circular closed path parallel to the closed loop of the inductor's magnetic field.