Crystal structure effect of ferromagnetic electrode on tunneling magnetoresistance

We show experimentally the effect of the crystal structure of a ferromagnetic (FM) electrode on tunneling magnetoresistance (TMR) by changing only the crystal structure of the bottom FM electrode in a magnetic tunnel junction (MTJ) and observing a significant TMR difference. Co87Fe13 was selected as the bottom FM electrode because the difference in stability between its face-centered cubic (fcc) and body-centered cubic (bcc) structures is very small. This enables us to compare the TMR of MTJs comprising ferromagnetic layers at the same composition but with different crystal structures. We find a significant increase in the TMR when changing from an fcc-Co87Fe13 to bcc-Co87Fe13 bottom FM electrode. The structurally induced TMR enhancement is attributed to a higher s-electron spin polarization for the bcc structure, which was confirmed for bulk Co and Co87.5Fe12.5 by ab initio calculations. These results unambiguously demonstrate the role of crystal structure and the associated electronic structure of FM electrodes in spin-dependent tunneling.