A method is disclosed for operating a computing device. The central portion occupies 80 to 99% of a distance from a center to an outermost surface of the particle and the surface portion occupies 20 to 1% of the distance. The writing method for the MRAM using the bipolar junction transistor writes data by applying current from the emitter to the collector, and changing a magnetization direction of a free ferromagnetic layer of the MTJ cell by a magnetic field generated due to the current. The insertion member keeps the optical assembly in contact with the first portion when the substrate is moved away from being disposed adjacent to the optical assembly.