MgO/Fe(001) and $\text{MgO}/\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ interfaces for magnetic tunnel junctions: A comparative study

The chemical, structural, and electronic properties of MgO/Fe(001) and $\text{MgO}/\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ interfaces for magnetic tunnel junctions (MTJs) have been widely investigated by means of electron spectroscopy. In particular, we present a detailed analysis of the spin-resolved electronic structure above the Fermi level, carried out by spin-polarized inverse photoemission and absorbed current spectroscopy. The MgO barrier presents good crystallinity and sharp interfaces when grown both onto Fe(001) and $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$. Moreover, we find that the exchange splitting of unoccupied bands is essentially the same for the two MgO/Fe interfaces, even though it is different for the two starting surfaces, being larger in $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ than in Fe(001). Our findings indicate that $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ is a good candidate for the realization of heterostructures for magnetic tunnel junctions because of its high chemical stability and reproducibility, as compared to clean Fe(001).

Figure 1

(Color online) LEED pattern taken on (a) 2 ML of MgO on Fe(001), (b) 2 ML of MgO on $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$, (c) 4 ML of MgO on $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ grown at RT, and (d) 4 ML of MgO on $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ after annealing A1 at 570 K.

Figure 2

(Color online) Fe2p XPS spectra taken at $60°$ of collection angle and at different MgO coverage on Fe(001) (upper panel) and $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ (lower panel). A1 and A2 indicate different annealing treatments (see text). The hatched area represents the contribution of Fe atoms interacting with O to the spectrum from $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$.

Figure 3

(Color online) SPIPE data for different MgO coverage on Fe(001). The position of the MgO gap is indicated on the energy scale with a thick green line. The blue curves are the result of a smoothing of the majority spectrum in the region of the image state(s), whose position is marked with a triangle.

Figure 4

(Color online) SPIPE data for different MgO coverage and annealing treatments on $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$. The position of the MgO gap is indicated on the energy scale with a thick green line. The blue curves are the result of a smoothing of the majority spectrum in the region of the image state(s), whose position is marked with a triangle.