The effect of indium contamination and Nb contact layers on the structure of Ag/NiFe GMR spin valves

Ag/NiFe/Ag/NiFe/FeMn giant magnetoresistance (GMR) spin valves (SVs), sputtered either on to a Nb superconducting contact or directly on to a Si substrate, were examined using conventional transmission electron microscopy (CTEM), high-resolution transmission electron microscopy (HRTEM), and high-resolution energy dispersive X-ray spectroscopy (HREDS). When sputtered on a superconducting Nb contact, the SV displayed columnar, polycrystalline grains, which grew on the close packed planes (i.e. {110} planes for the bcc Nb contacts and {111} planes for the fcc Ag, NiFe and FeMn spin valve components). When grown directly on the Si substrate, two different SV morphologies were observed. In most cases, the spin valves appeared polycrystalline, similar to those grown on Nb. However, in one case, the first Ag layer grew as an epitaxial single crystal throughout the entire observed area of the cross-sectional sample. The subsequently deposited layers displayed polycrystalline columnar morphology of the equilibrium phases. Fast Fourier transform (FFT) analysis of HRTEM images indicated that this single crystal Ag layer existed in an unusual crystal structure. HREDS of the spin valve grown directly on the Si substrate showed little mixing of the expected spin valve layers. However, analysis of the single crystal Ag layer in this area revealed the presence of an indium contaminant, which may be responsible for the epitaxial growth of this layer.