Abstract
A CoPt/MgO/CoPt tri-layer film is prepared on an Ru(0001) single-crystal underlayer at 300 °C by ultra-high vacuum magnetron sputtering. The growth behavior and the crystallographic properties are investigated by reflection high-energy electron diffraction, x-ray diffraction, and cross-sectional transmission electron microscopy. A fully epitaxial CoPt/MgO/CoPt film is formed on the Ru underlayer. The lower CoPt, the MgO, and the upper CoPt layers consist of two (111) variants whose atomic stacking sequences of close-packed plane along the perpendicular direction are ABCABC... and ACBACB... The lower and the upper CoPt layers involve metastable L11 structure, whereas the crystal structure of MgO layer is B1. Flat and atomically sharp interfaces are formed between the layers. The tri-layer film shows a strong perpendicular magnetic anisotropy reflecting the magnetocrystalline anisotropy of L11 crystal. The present study shows that an epitaxial L11-CoPt/MgO/L11-CoPt tri-layer film with perpendicular magnetic anisotropy can be formed by using a low substrate temperature of 300 °C.
Highlights
Magnetic tunnel junctions consist of tunnel barrier and ferromagnetic electrode layers and have been studied for applications like tunnel magnetoresistance (TMR) sensors and magnetoresistive random access memory (MRAM) devices
Flat and atomically sharp interfaces are formed between the layers
The present study shows that an epitaxial L11-CoPt/MgO/L11-CoPt tri-layer film with perpendicular magnetic anisotropy can be formed by using a low substrate temperature of 300 ◦C
Summary
Magnetic tunnel junctions consist of tunnel barrier and ferromagnetic electrode layers and have been studied for applications like tunnel magnetoresistance (TMR) sensors and magnetoresistive random access memory (MRAM) devices. In order to achieve high TMR ratios, highly-oriented polycrystalline[1] or epitaxial single-crystal[2] MgO layer is effective as the barrier layer. For MRAM device applications, magnetic materials with high uniaxial magnetocrystalline anisotropy (Ku) energies are required as the electrode material. L10 ordered FePt3 and CoPt4 alloys show Ku greater than 107 erg/cm[3] along [001]. CoPt crystal with metastable L11 phase shows Ku greater than 107 erg/cm[3] along [111]7,8 and the (111)-oriented films have been prepared by employing a lower temperature around 300 ◦C.7–14. A CoPt/MgO/CoPt tri-layer film is prepared on an Ru(0001) single-crystal underlayer. The growth behavior, the crystal structure, the microstructure, and the magnetic properties are investigated
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