Characterization of ion-beam-sputtered magnetic thin films for sensor applications.

摘要

Ion beam deposition processes were utilized to fabricate giant magnetoresistive (GMR) spin valves and hard magnetic films used in magnetic recording heads. Ion-beam-sputtered GMR spin valves showed stronger exchange coupling and higher thermal stability than those deposited by means of magnetron sputtering. Exchange coupling constants of 0.133 erg/cm2 and 0.182 erg/cm 2 were determined for NiFe/FeMn films and CoFe/IrMn films, respectively. A DeltaR/R value of 9% was measured for an IrMn-based spin valve. Synthetic spin valve structures were also fabricated, showing enhanced exchange coupling strength and thermal stability. A dual-energy process combining optimal crystal structure with minimized interlayer mixing and surface roughness was employed to improve GMR-performance. A coercivity of greater than 2100 Oe was obtained for a Cr-50A/CoCrPt-250A film. The collimation of ion-beam-sputtered target materials was exploited to achieve excellent lift-off profile for permanent magnet bias application.Increased interface mixing and surface roughness, related to deposition parameters such as process gas and beam energy, were found to be detrimental to both exchange coupling and GMR performance of the spin valves. Interlayer coupling between the free layer and the pinned layer was attributed to the interface roughness and explained successfully by Neel's "orange peel" model, as long as pinhole induced magnetostatic coupling could be ignored. Interfacial spin-dependent scattering and bulk spin-dependent scattering were both observed, while the contribution from the interface was found to be dominant. The dependence of blocking temperature on the antiferromagnetic layer thickness could be interpreted in terms of finite-size scaling effect. The channeling mechanism of energetic ions into the substrate was used to explain the correlation between the crystal orientation of the hard magnetic films and the assist beam energy.