We present a systematic and detailed study of the magnetization reversal process and magnetotransport properties of ${\mathrm{Fe}}_3{\mathrm{O}}_4∕\mathrm{Cu}$ $\left(t_{\mathrm{Cu}}\right)∕{\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ spin valve structures. A drastic change was observed in both the magnetic and transport properties as the thickness of the Cu spacer layer $t_{\mathrm{Cu}}$ was varied in the range $2\mathrm{nm}⩽t_{\mathrm{Cu}}⩽30\mathrm{nm}$. For $t_{\mathrm{Cu}}=2\mathrm{nm}$, the transport properties are mainly due to anisotropic magnetoresistance effects because of strong exchange coupling between the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ and ${\mathrm{Fe}}_3{\mathrm{O}}_4$ layers. For $t_{\mathrm{Cu}}⩾5\mathrm{nm}$, however, the transport properties are dominated by positive giant magnetoresistance (GMR) effects due to separate magnetization switching of the two magnetic layers. The GMR ratio decreases with increasing spacer layer thickness due to enhanced current shunting and scattering effects. We also observed that the GMR ratio has strong temperature dependence and decreases with increasing temperature due to spin flip scattering and electron-magnon interactions.

• Received 20 June 2006

DOI:https://doi.org/10.1103/PhysRevB.75.012403