MgO Underlayer Research Articles

Structure and magnetic properties of L1 CoPt(Ag/MgO,MgO) thin films

Disordered fcc (face-centered-cubic) [100] fiber-textured CoPt thin films with thicknesses of 20–40 nm were deposited on a nonmagnetic sputtered MgO seed layer with and without a Ag intermediate layer. These were subsequently annealed at 600–750 °C for 5–10 min using rapid thermal annealing (RTA). The structural variants were determined to coexist in the in-plane and normal to the plane directions after the RTA process. The MgO underlayer without the intermediate layer revealed strong in-plane anisotropy by magnetic hysteresis measurement. Selected area diffraction (SAD) by TEM and XRD measurements for these samples confirmed the preferential growth of in-plane variants of c axis compared to the perpendicular direction. High remanence and coercive squareness (S*) were obtained due to strong in-plane texture and especially due to exchange coupling among the grains. Evidence for this was provided by ΔM curves. Initial magnetization curves for samples annealed above 600 °C, showed the possibility of assembled single domain or domain pinning mechanism but with negligible free wall motion inside of the grains.

Magnetic properties of nanostructured CoPt and FePt thin films

Polycrystalline MgO underlayer films lead to different preferred orientations of L1/sub 0/ CoPt and FePt films after the annealing process, depending on the thickness of the L1/sub 0/ films. L1/sub 0/ films with a thickness greater than 20 nm revealed mostly L1/sub 0/ [100] fiber texture and consequently in-plane anisotropy as determined by magnetic hysteresis. Strong perpendicular anisotropy due to the L1/sub 0/ [001] fiber texture was obtained for thicknesses below 10 nm. The /spl delta/M curve showed strong intergranular exchange coupling. The angular variation of coercivity showed the possibility of both domain wall motion and a rotational mechanism of magnetization reversal.

Sectional structures and electrical properties of ultrathin NbN/MgO bilayers on Si(100)

NbN/MgO bilayers deposited on Si(100) substrates by rf-sputtering were studied using cross-sectional transmission electron microscopy (XTEM). The XTEM results reveal that the 10-nm-thick MgO layer forms two layers of different structures, i.e., an amorphous layer (∼4 nm) and a highly (100) oriented polycrystalline layer (∼6 nm). We also found that the structure of MgO underlayers exhibits a strong effect on Tc of on-deposited NbN layers.

NbN/MgO/NbN Josephson tunnel junctions fabricated on thin underlayers of MgO

Underlayers of MgO as thin as 8.0 nm have been used in the fabrication of NbN/MgO/NbN Josephson tunnel junctions. NbN/MgO/NbN trilayers with and without MgO underlayers were deposited on thermally oxidized Si substrates at 100 degrees C using RF magnetron sputtering in a semi-UHV (ultrahigh vacuum) load lock vacuum system. Sputtering parameters were first optimized to produce NbN with T/sub c/=14.7 K on SiO/sub 2//Si substrates, and then thin MgO underlayers were used to enhance the T/sub c/ of the trilayers to 15.7 K. X-ray diffraction of NbN films indicates that thin MgO underlayers of 8.0 nm are capable of almost completely removing the NbN [111] diffraction peak found in lower T/sub c/ films and enhancing the NbN [200] peak. MgO underlayers were found to be oriented in the [100] direction when sputtered in an atmosphere of Ar and N/sub 2/ and randomly oriented when sputtered in Ar alone. The authors present details for the preparation and analysis of NbN and MgO films as well as the fabrication and electrical performance of tunnel junctions with and without MgO underlayers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>