Transport Properties in Sputtered CoFeB/MgAl2O4/CoFeB Magnetic Tunnel Junctions

CoFeB/MgAl₂O₄/CoFeB magnetic tunnel junctions (MTJs) with the barrier sputtered from sintered MgAl₂O₄ target have been successfully fabricated. Dependence of tunneling magnetoresistance (TMR) ratio on both MgAl₂O₄ deposition pressure and postannealing temperature has been studied. The TMR ratio of more than 50% at room temperature was obtained with an annealing temperature of 325 °C and MgAl₂O₄ deposition pressure of 1.3 Pa. Temperature dependence of resistance in both parallel and antiparallel configurations can be well fitted by the model based on direct elastic tunneling and magnon-assisted inelastic tunneling. Inelastic electron tunneling spectroscopy (IETS) at low temperature, exhibiting three peaks originating from zero-bias anomaly, interface magnons, and barrier phonons, were measured and compared with the results of AlO_x and MgO-based MTJs. The IETS for all three types of MTJs shows quite similar peak positions for all kinds of elementary excitations except barrier phonons.