Planar Hall effect of Permalloy films on Si(111), Si(100), and glass substrates

Abstract

Different thicknesses, tf=7.5–100 nm, of Permalloy (Py) films were deposited on Si(111), Si(100), and glass substrates, respectively, at Ts=270 °C. The sensitivities (SH) of the planar Hall effect (PHE) and temperature coefficient of resistance (TCR) of the film samples were measured from room temperature to T=250 °C. When 10 nm≤tf≤100 nm, SH increases as tf decreases, in agreement with theory. However, when tf<10 nm, SH decreases instead due to the coalescence condition, as indicated by an abnormal increase in the sheet resistance R◻ of the film sample. Moreover, we have studied the nonlinear deviation of the PHE signal at field |H|=6 Oe, defined as ξ, and the temperature stability of PHE sensitivity as [△SH/△T]. In summary, we find (A) the Py(10 nm)/Si(111) sample has the highest SH(RT)=340 Ω/T because its surface is the smoothest with the lowest anisotropy field Hk; (B) the other properties, such as ξ, [△SH/△T], and TCR, of the Py(10 nm)/Si(111) sample are inferior to those of the Py(10 nm)/glass sample; (C) ξ remains almost the same, as RT≤T≤100 °C; (D) negative TCR values of the Py/Si(111) and Py/Si(100) samples are related to the substrate contributions, e.g., TCR, thermal expansion coefficient α, and thermoelectric power β of Si.