Magnetic Devices Using Rare-Earth Nitrides

This thesis uses (Gd,Sm)N as the ferromagnetic layers in a thin film tri-layer magnetic memory element. The relative alignment of the (Gd,Sm)N layers were written with an applied magnetic field. The non-magnetic metallic blocking layers between the (Gd,Sm)N layers of silver and aluminium were chosen for low-Impedance read-out, however both formed interface layers when (Gd,Sm)N was grown on top of the metal. The structural and magnetic properties of epitaxial and polycrystalline (GdxSm1−x)N were found to be suitable for the tri-layer structure. The switching layers were either epitaxial GdN or polycrystalline Gd-rich (Gd,Sm)N and the fixed layer as polycrystalline Sm-rich (Gd,Sm)N.

The tri-layers had contrasting aligned and anti-aligned state remanent moments, which can be altered by the chosen structure and switching fields. The states are re-writeable with moderate magnetic fields (in order 0.1 T) and stable in no applied field over 16.5 hours. The tri-layers were formed into islands using two methods. The post-growth milling method on an existing tri-layer film demonstrated the magnetic properties were retained for 30 μm islands. The pre-patterned photo-resist method showed characteristic tri-layer magnetic behaviour of 5 μm islands.

These measurements demonstrate that a (Gd,Sm)N based thin film tri- layer island could be used with fringe-field sensing device as a cryogenic memory element. Further optimisation of the chosen (Gd,Sm)N layers and writing methods is required for development into a fully functioning cryogenic memory.