Designs of higher tunnelling giant magnetoresistance in granular films

Based on Inoue's model (Ref. [J. Inoue, S. Maekawa, Phys. Rev. B 53 (1996) R11927.]) and our modified model (Ref. [C.Z. Wang, Z.H.Guo, Y.H. Rong, T.Y. Hsu, Phys. Lett. A. 329(2004)236.]) on intrinsic factors of granular films influencing tunneling giant magnetoresistance (TMR), we designed various kinds of ferromagnetic metals–insulator granular films, including Fe–Al2O3, FeCo–Al2O3, CoNi–Al2O3 and FeCo–SiO2 with different ferromagnetic granules, matrices and the size distribution of ferromagnetic granules. The results indicated that the approaches obtained higher TMR are alloying, such as FeCo instead of Fe, and selection of matrix, such as Al2O3 instead of SiO2, as well as a proper size distribution of ferromagnetic granules where single domain granules should play a key role in TMR. Moreover, TMR (6.9%) of FeCo–Al2O3 granular film, so far the highest value reported at room temperature and under applied field of 12.5 K Oe, was obtained in this work.