Spintronic Devices For Memory and Sensor Applications
Abstract: Adding spin functionality to nano-electronic devices enables many important applications such as ultra-high density data storage, on-chip microwave generation, and spin logic. The surprisingly high diversity in spin configurations that emerge when bulk magnets are patterned into nano-dimensions created an attractive research area aimed at determining dynamic and static properties of such spin configurations. These studies are paving the way to energy efficient, low-cost and reliable memory, radio frequency oscillator and detector devices. Lately the dynamic behavior of such nanomagnetic devices have gained importance in the relatively unexplored temperature regime in the vicinity of the Curie point especially due to potential applications in thermally assisted recording schemes. A study of the elevated temperature nature of switching dynamics of magnetic bits requires a formalism that takes into account both longitudinal and transverse magnetization relaxation mechanisms in addition to temperature dependent damping parameters. All such effects are conventionally disregarded within the Landau-Lifshitz-Gilbert (LLG) framework.. The essential motivation of the current work is to develop a Stochastic-LLB based macrospin model, using experimentally measured temperature dependence of intrinsic parameters for CoNi/Pd multilayers as realistic material parameters. Such a model enables us to determine the temperature dependence of longitudinal susceptibility from single fit simulations of experimental switching data consistent with previous ab-initio calculations. A map of switching time as a function of magnetic field and heating pulses together with a visualization of the granular switching process is obtained.
Such high temperature dynamics is also potentially applicable to emerging three dimensional memory technologies as well. We have investigated heat-assisted domain transfer in a magnetic multilayer nanowire stack with perpendicular anisotropy using locally applied fields. 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 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.
Reminder: Tea and cookies will be in the seminar room before the seminar.