Synthesis of Cobalt Nanoparticle and Fabrication of Magnetoresistance Devices by Ion-Assisted Aerosol Generation Method

The ionization chemical vapor deposition (ionization CVD) method, which is one of the ion-assisted aerosol generation methods, was used to synthesize Co nanoparticles and fabricate a magnetoresistance device using them. A cobalt tricarbonyl nitrosyl vapor is ionized by a high-pressure ionizer before being fed into the reactor. It reacts and forms nanoparticles by a thermal decomposition reaction in the furnace reactor. Particles deposit electrostatically on an insulator substrate that has two Au electrodes and fill the gap between the electrodes. This Co-nanoparticle device is then annealed under hydrogen gas to deoxidize the deposited particles. After annealing, two copper wires are attached to the two Au electrodes to connect with a DC voltage supplier and an ammeter. The magnetoresistance of the device was evaluated by measuring its electrical resistance using a superconducting quantum interference device (SQUID) magnetometer. The X-ray diffraction patterns of the nanoparticles before and after annealing revealed CoO and Co, respectively. Two fabricated devices with number densities of Co nanoparticles of 4.25 × 10¹⁰ and 1.16 × 10¹¹ cm^?2 showed magnetoresistance ratios of 73% and 1002%, respectively, at an applied voltage of 30 V, a measurement temperature of 5 K, and a magnetic field of ?1 ～ 1 T. It was found from the experimental results that the method developed in this article was useful to fabricate the Co-nanoparticle magnetoresistance device.