The effect of NiFeCr seed layer composition on the giant magnetoresistance properties of [FeCoNi/Cu] multilayers

Abstract

We present a systematic study on the giant magnetoresistance (GMR) and interlayer exchange couplings (IEC) in polycrystalline [Fe16Co66Ni18/Cu]5/Fe16Co66Ni18 multilayer films deposited on NiFeCr seed layers with various compositions. We observed that the GMR ratio (ΔR/R) depends on bilinear and biquadratic IEC coefficients, J1 and J2, and varies linearly with their ratio, J1/J2. The maximum ΔR/R of 35 ± 2.5% and strong antiparallel IEC (J1/J2 > 1) were observed for the seed layers with a particular Ni:Fe ratio of (Ni0.55Cr0.45)100-yFey with 0 ≤ y ≤ 47 at. %. Structural studies confirm that the high ΔR/R and J1/J2 for these NiFeCr compositions are related to a strong fcc [111] crystallographic texture and a coarse grain size of the FeCoNi/Cu mutilayers. In addition, we observed that the film deposited on a Ni32Fe33Cr35 seed layer showed a stronger [111] texture, but a lower ΔR/R (17%) than those deposited on a Ni36Fe51Cr13 seed layer (ΔR/R = 28%). Detailed microstructural analysis indicated an increased arithmetic average roughness (Ra) of the interfaces between FeCoNi and Cu layers for the films with the Ni32Fe33Cr35 seed layer. We argue that the lower ΔR/R in the film despite the relatively strong [111] texture is due to its higher Ra which causes a reduction in antiparallel IEC. This indicates that two conditions of (i) a strong [111] crystallographic texture and (ii) small interface roughness must be satisfied in the FeCoNi/Cu multilayer to achieve a strong antiparallel IEC and thus large ΔR/R.