Magnetic Nanoparticle Detection Using Wheatstone Bridge Giant Magnetoresistance (GMR) Sensor with Double CoFeB Spin-Valve Thin Films

摘要

The Wheatstone bridge-giant magnetoresistance (GMR) sensor with single and double spin valve thin film was successfully developed for potential biomolecular detection. The GMR sensor with spin valves structure of [Ta (2nm)/IrMn (10nm)/CoFe (3nm)/Cu (2,2nm)/CoFeB (10nm)/Ta (5nm)] was fabricated using DC Magnetic Sputtering method. The Fe_3O_4 magnetic nanoparticles were synthesized by the co-precipitation method as a magnetic label. The magnetic properties of the Fe_3O_4 nanoparticles measured are the saturation magnetization (Ms) of 77.7 emu/g, remanence magnetization (Mr) of 7.7 emu/g, and coercivity (Hc) of 49 Oe. The X-ray diffraction pattern showed the inverse cubic spinel structure with an average crystal size of about 20.1 nm. Fe_3O_4 magnetic nanoparticles with various concentrations were used to be detected using a GMR sensor. The output voltage of the GMR sensor with the single and double spin-valve increased from 1.7 to 3.9 mV and 2.9 to 5.3 mV with the increase of the Fe_3O_4 concentration from 0 to 20 mg/mL, respectively.