Thermal Annealing Effects on the Structural, Magnetic, and Magnetotransport Properties of NiFe/(Ni,Fe)O Bilayers

Abstract

In this study, the exchange bias and magnetoresistance of NiFe/(Ni,Fe)O bilayers were investigated. Transmission electron microscopy has shown that the (Ni,Fe)O single layer is a pure rock-salt solid solution (a = 4.24 angstrom). After annealing at 500 degrees C for 2 h, the (Ni,Fe)O film undergoes a phase transformation from the pure antiferromagnetic (Ni,Fe)O into ferromagnetic Ni (a = 3.53 angstrom) and ferrimagnetic NiFe(2)O(4) (a = 8.29 angstrom) phases. Furthermore, the NiFe/as-deposited (Ni,Fe)O bilayers exhibit a strong temperature dependence of exchange bias field [H(ex) (T)] that increases linearly with decreasing temperature (H(ex) = -30Oe at 150 K). Surprisingly, no H(ex) was observed in the NiFe/ annealed (Ni,Fe)O bilayers, even at 150 K. This indicates that the AF (Ni,Fe)O phase provides stronger exchange coupling than the ferrimagnetic NiFe(2)O(4). Magnetotransport measurements have shown that these NiFe/(Ni,Fe)O bilayers exhibit anisotropic magnetoresistance (AMR). The NiFe/as-deposited (Ni,Fe)O bilayers exhibit a higher MR ratio than the NiFe/annealed (Ni,Fe)O bilayers, which suggests stronger anisotropic electron scattering between the NiFe and (Ni,Fe)O interfaces in the annealed system. (C) 2009 The Japan Society of Applied Physic

Magnetometry and transport data complement polarized neutron reflectometry in magnetic depth profiling

“…The negative AMR value DR/R 0 ¼ À0.46% is quite typical for sputtered Permalloy films, 27 confirming the validity of our approach and thus confirming the Stoner-Wohlfarth-type uniform rotation of the top NiFe layer. Likewise R 0 ¼ ql= at ð Þ is consistent with the calculation from the resistivity value, 28,29 q ¼16 lXcm, and the sample geometry l ¼ 1 cm, a ¼ 0.5 cm, and the film thickness t ¼ 0.45 lm which yields R 0 ¼ 0:72 X within 3% accuracy of the fitting result.…”