Studies In Nanomagnetism: Co/Ni Multilayers In Magnetic Tunnel Junctions, Nanomagnets In Superconducting Microwave Cavities, And Magnetic Multilayer Nanowires

by Theodore Gudmundsen

Institution: Cornell University
Year: 2014
Keywords: Nanomagnetics ; MRAM ; Magnetism
Record ID: 2041845
Full text PDF: http://hdl.handle.net/1813/36034


Three experiments in nanomagnetism were performed. In the first, we reduced the switching current of a magnetic tunnel junction by incorporating Co/Ni films possessing perpendicular magnetic anisotropy (PMA). We characterized Co/Ni films with vibrating sample magnetometry and ferromagnetic resonance and measured a PMA of 0.22-0.26 mJ/m2 . By combining Co/Ni films with FeCoB in the electrodes, we reduced the demagnetization field of the free layer from 13000 Oe to 2000 Oe, while maintaining a low damping of only .015. These [Co/Ni]/FeCoB devices had 106% TMR at maximum, and 38% in a device with resistance below 10 Ω-um2 that was spin-torque switchable. We demonstrated spin-torque switching in magnetic tunnel junctions of this kind, and saw some reduction of the switching current compared to similar devices in the literature. In the second project, I endeavored to design a niobium superconducting microwave cavity that I could strongly couple to a nanomagnet for a variety of scientific and technological applications. Towards that end, I successfully designed, fabricated, and packaged a 50 ohm superconducting cavity in the coplanar waveguide geometry with an unprecedently thin center line of 476 nm. Under cryogenic conditions, the cavity showed a quality factor of 566 at 5.9 GHz. In the third project, I designed an electrically switchable three-terminal device for injecting spin currents into semiconductors. The device consists of a multilayer magnetic nanowire with a domain wall that can be moved by spin-torque transfer. I designed a fabrication recipe to make that device, and made significant progress towards fabricating a complete device, including the demonstration of the lithography for all four layers.