In-situ magnetic deposition field effect on sheet resistance of Permalloy films

We have measured the real-time in-situ sheet resistance (R□) of a Permalloy (Py) film during the film-growth period in a vacuum under various magnetic deposition-field (H) conditions: a longitudinal direct-current (dc) field (H = Hx), a transverse dc field (H = Hy), and a rotating field (H = Hr) with the frequency (f) at 0.6, 1.4, 2.5, 10, and 100 Hz, respectively. The results show that R□(Hy) > R□(Hx) ≃ R□(H = 0) ≫ R□(H = Hr), when Py film is just before or near the coalescence stage of the film-growth process. The reason for these phenomena is that a dc field (H = 0, Hx, or Hy) tends to make the structure of the film more anisotropic, while a rotating field (H = Hr) tends to make the film more isotropic. Moreover, based on the quantum tunneling mechanism, the fact that there will be many more tunneling events through which an electron can be transported down a piece-by-piece connected film with an anisotropic than with an isotropic structure should naturally lead to the observed results above. Finally, we also explain why in the R□ versus f plot (under the condition of film thickness tf = 1 nm), there exists a minimum R□ at f = fmin = 2.5 Hz.