Three Dimensional Magnetic Memory
Yemliha Bilal Kalyoncu, Aisha Gokce Ozbay
in collaboration with HGST
Future limitations to the improvements in the data storage density with perpendicular recording act as a driving force for an intensive effort to investigate alternative schemes to reliably store and recall information with ultra-high density on magnetic media. There are several approaches for achieving this goal, such as thermally-assisted recording, microwave assisted recording and ultimately 3-d magnetic storage schemes. IBM has already demonstrated race track memory in which magnetic domains (bits) are moved along a 3D magnetic wire by applying spin-polarized current pulses . Here we will present our investigation of heat-assisted domain transfer in a magnetic multilayer nanowire stack with perpendicular anisotropy using locally applied fields. A recent study in continuous film [CoNi/Pd]/Pd/ [Co/Pd] multilayer stacks has unambiguously shown stray field induced domain replication using element-specific x-ray imaging techniques . For storage device applications it is crucial to understand and gain full control over the conditions that lead to reproducible stray field induced single domain transfer in patterned magnetic nanostructures. For this purpose we have fabricated single magnetic layer (CoNi/Pd) nanowires as well as devices that consist of a SiN-CoNi/Pd-SiN-CoNi/Pd-Ta stack with 50-100 nm constrictions in a cross-wire configuration to study domain transfer between magnetic layers. We use the localized stray field from a magnetic tip to write single-domains in the CoNi/Pd magnetic layer by modulating its coercivity via instantaneous and localized heating from a current pulse .We investigate resulting domain structure in nanowires with various widths as a function of the current pulse amplitude and width to vary the local temperature and the tip height to vary the local field. We also work on the nature of current-induced demagnetization limit and thermally-induced domain transfer between magnetic layers This study establishes the preliminary conditions for the use of 3-D integrated cross-wires of perpendicular anisotropy magnetic materials to boost the data storage capacity of future magnetic memory devices.
This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the Contract No. 112T205 & Bogazici University Research Fund under the Contract No. 13B03P6
 S.S.P. Parkin, M. Hayashi, L. Thomas, Science 320, 190(2008)
 T. Hauet, C. Günther, B. Pfau, M. Schabes, J.-U. Thiele, R. L. Rick, P. Fischer, S. Eisebitt, and O. Hellwig, Phys. Rev. B 77, 184421 (2008).
O.Ozatay and B. D. Terris Read / Write Structures for a Three Dimensional Memory US Patent# 8164940