Magnetization reversal and magnetic anisotropies in epitaxial Fe/MgO and Fe/MgO/Fe heterostructures grown on Si(001)

Abstract

Epitaxial Fe/MgO heterostructures have been grown on Si͑001͒ by a combination of sputtering and laser ablation deposition techniques. The growth of MgO on Si͑001͒ is mainly determined by the nature of the interface, with large lattice mismatch and the presence of an amorphous layer of unclear origin. Reflection high energy electron diffraction patterns of this MgO buffer layer are characteristic of an epitaxial, but disordered, structure. The structural quality of subsequent Fe and MgO layers continuously improves due to the better lattice match and the burial of defects. A weak uniaxial in-plane magnetic anisotropy is found superimposed on the expected cubic biaxial anisotropy. This additional anisotropy, of interfacial nature and often found in Fe/MgO and Fe/ MgO/GaAs͑001͒ systems, is less intense here due to the poorer MgO/Si interface quality compared with that of other systems. From the evolution of the anisotropy field with film thickness, magnetic anisotropy is also found to depend on the crystal quality. Kerr measurements of a Fe/MgO multilayered structure grown on Si show two different switching fields, suggesting magnetic coupling of two of the three Fe layers. Nevertheless, due to the little sensitivity to the bottom Fe film, independent switching of the three layers cannot be ruled out.

Magnetism of Amorphous and Nano-Crystallized Dc-Sputter-Deposited MgO Thin Films

“…Peaks related to MgO were not observed in the XRD patterns of the samples indicating that the films are mostly amorphous in the as-grown state. Large lattice mismatch (22.4%) between MgO (0.4213 nm) and Si (0.543 nm) and a large difference in thermal expansion coefficients (MgO: 13.5 × 10 −6 /°C, Si: 4.0 × 10 −6 /°C) hinder the possible epitaxial growth of MgO on Si substrates [ 23 , 24 ]. The film deposited with the P O2 of 10% shows a broad peak at about 42°.…”

Epitaxial growth of MgO and Fe∕MgO∕Fe magnetic tunnel junctions on (100)-Si by molecular beam epitaxy

“…[12][13][14] Methods such as laser ablation and magnetron sputtering are more commonly applied as the excess energy involved helps establishing epitaxial correlations. [15][16][17][18][19][20][21] On the other hand, epitaxial growth of MgO on GaAs with e-beam evaporation is well documented in literature [22][23][24] due to much better lattice matching ͑−0.7% ͒. In this letter, we demonstrate the epitaxial growth of thin ͑100͒-MgO films on top of ͑100͒-Si substrates.…”

Epitaxial Growth of Fe/MgO/Fe Heterostructures on SrTiO3(001) Substrates by Magnetron Sputtering

“…Several groups have reported on the epitaxy of Fe/MgO/Fe trilayers fabricated by molecularbeam epitaxy (MBE) on MgO(001) substrates, 12) or by sputtering in combination with laser-ablation deposition on GaAs(001) and Si(001) substrates. 13,14) Recently, TMR ratios as high as 180% at room temperature (RT) have been reported for epitaxially grown Fe/MgO/Fe MTJs fabricated by MBE. [15][16][17] From a practical point of view, however, a magnetron sputtering method for fabricating MTJs would be preferable because of the compatibility with existing LSI processes.…”