Giant magnetoresistnace in magnetic multilayer Co/Cu system irradiated with 23 MeV proton

摘要

The magnetic multilayer Co/Cu system composed of alternate thin layers of Cu and Co is prepared on Si wafer by molecular beam epitaxy (MBE) technique. The layer thickness is varied from 100 A to 1000 A. The deposition parameters like the rate of deposition, substrate temperature and the level of vacuum are standardized in order to prepare high quality epitaxial films. The degree of epitaxy is studied by the reflection high energy electron diffraction (RHEED) patterns. The films are subsequently irradiated with high energy (28 Mev) proton beams having different fluences (10~(12)-10~(14) ions/cm~2) which lead to the development of lattice defects. The role of such defects in modulating the interlayer magnetic exchange interaction, magnetocrystalline anisotropy and the magnetoresistance in such multilayer system is studied. From the observed patterns of variation in the saturation magnetization M_s and the corresponding field H_s with the layer thickness we have calculated the magnetic hysteresis curve and M-axis we have calculated the magnetic anisotropy energy K_u. By plotting K_u(d_(Co)+d_(Cu))vs. d_(Co)(where 'd' is thickness of a layer) we could calculate the bulk and interface anisotropy K_v and K_s. The variation in these parameters with the radiation fluence is noted which helps in quantitatively estimating the extent of defects in the bulk and the interface region. Interestingly, even though the saturation magnetization M_s is dropped due to irradiation, the corresponding field and the coercive field have improved which are significant from the point of view of application of these multilayers as magnetic sensors. These observations highlight that it is possible to suitably modify the extent of radiation defects in order to improve the magnetoresistivity as well.