Although current in-plane giant magnetoresistance (CIP-GMR) is widely used as various magnetic field sensors, a higher magnetoresistance (MR) ratio is still required to improve their sensitivity and detectivity for certain applications. Here, we report dramatic enhancement of the MR ratio up to 26.5% in a spin valve device and 40.5% in an antiferromagnetically coupled trilayer device using fully epitaxial Co50Fe50/Cu/Co50Fe50 structures with metastable bcc-Cu spacer layers. Transmission electron microscopy analysis indicated that the metastable bcc-Cu had a perfect lattice match at the bcc-Co50Fe50/bcc-Cu interfaces. First-principles calculations showed good electronic band matching that induces a large spin asymmetry of the electron transmittance in the in-plane direction. The combination of this substantial lattice match and electronic band match is attributed to the large MR ratio, suggesting that exploring the use of metastable structure in ferromagnetic/nonferromagnetic multilayers will lead to further enhancement of CIP-GMR.
