Experimental evidence of the spin dependence of electron reflections in magnetic ${\mathrm{CoFe}}_2{\mathrm{O}}_4∕\mathrm{Au}∕{\mathrm{Fe}}_3{\mathrm{O}}_4$ trilayers

An original epitaxial system consisting of two ferrimagnetic insulator layers (${\mathrm{CoFe}}_2{\mathrm{O}}_4$ and ${\mathrm{Fe}}_3{\mathrm{O}}_4$) separated by a nonmagnetic metallic layer (Au) has been grown. The transport properties in the current in plane geometry indicate that the conduction of the ${\mathrm{CoFe}}_2{\mathrm{O}}_4∕\mathrm{Au}∕{\mathrm{Fe}}_3{\mathrm{O}}_4$ trilayer takes place within the thin metallic layer. The giant magnetoresistance (GMR) observed (2.6% at $10\mathrm{K}$) is associated to the switching from a parallel to an antiparallel configuration of the magnetization of the two ferrite layers and corresponds to the spin dependence of electron reflection at the interfaces with a large contribution of specular reflections. The increase of the GMR (5% at $10\mathrm{K}$) in the symmetrical interface ${\mathrm{CoFe}}_2{\mathrm{O}}_4∕{\mathrm{Fe}}_3{\mathrm{O}}_4∕\mathrm{Au}∕{\mathrm{Fe}}_3{\mathrm{O}}_4$ system and the effect of the interface roughness on the GMR confirm the presence of this spin-dependent specular reflection.

Figure 1

Low magnification TEM micrograph (a) and HRTEM image (b) of a $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3\left(0001\right)∕{\mathrm{CoFe}}_2{\mathrm{O}}_4\left(150\mathrm{nm}\right)∕\mathrm{Au}\left(10.2\mathrm{nm}\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(120\mathrm{nm}\right)$ trilayer studied along the $\left[\overline{1}10\right]$ zone axis.

Figure 2

Resistivity measurements as a function of temperature for the ${\mathrm{CoFe}}_2{\mathrm{O}}_4\left(150\mathrm{nm}\right)∕\mathrm{Au}\left(t\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(120\mathrm{nm}\right)$ trilayers with $t=10.2$ and $13.4\mathrm{nm}$.

Figure 3

Magnetic hysteresis loops (a) and magnetoresistances (b) obtained at $10\mathrm{K}$ on the ${\mathrm{CoFe}}_2{\mathrm{O}}_4\left(150\mathrm{nm}\right)∕\mathrm{Au}\left(t\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(120\mathrm{nm}\right)$ trilayers with $t=10.2\mathrm{nm}$ and $13.4\mathrm{nm}$.

Figure 4

Magnetoresistance obtained at $10\mathrm{K}$ on the symmetrical ${\mathrm{CoFe}}_2{\mathrm{O}}_4\left(200\mathrm{nm}\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(6\mathrm{nm}\right)∕\mathrm{Au}\left(7.2\mathrm{nm}\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(192\mathrm{nm}\right)$ and resistivity curve as a function of temperature inset.

Figure 5

HRTEM micrographs of the ${\mathrm{CoFe}}_2{\mathrm{O}}_4\left(150\mathrm{nm}\right)∕\mathrm{Au}\left(6.7\mathrm{nm}\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(100\mathrm{nm}\right)$ trilayers implanted at a dose of (a) ${10}^{13}$ and (b) ${10}^{15}\mathrm{ions}∕{\mathrm{cm}}^2$.

Figure 6

Magnetoresistance variations as a function of the fluences in ${\mathrm{CoFe}}_2{\mathrm{O}}_4\left(150\mathrm{nm}\right)∕\mathrm{Au}\left(6.7\mathrm{nm}\right)∕{\mathrm{Fe}}_3{\mathrm{O}}_4\left(100\mathrm{nm}\right)$ trilayers irradiated with ${\mathrm{N}}^{+}$ ions at $150\mathrm{keV}$ (normalized to the MR measured on the as deposited sample).