Invited Panelist: 51st Design Automation Conference

I will be serving as an invited panelist at the 51st Design Automation Conference CRAW/CDC Workshop May 31st-June 1st. See the link below for more details:

http://www2.dac.com/events/eventdetails.aspx?id=170-277

2013 MRS Fall Meeting Talk

I will be presenting our work:

 3:30 PM - U2.07 Topological Nature of Magnetic Vortices in Patterned Mesoscopic Disks

Functional magnetic materials have garnered interest due to the potential applications in the emerging field of spintronics. More specifically magnetic vortices have been widely studied due to the quasi-particle/topological nature and are described as having two degrees of freedom, polarity and chirality. While there has been several studies exploring the fascinating behavior of vortices under perturbations using electrical measurements, scanning probe microscopy, and synchrotron based x-ray techniques, transmission electron microscopy provides unparalleled high resolution magnetic and structural information. This allows for a detailed analysis on how the local structure of different materials affects the translation motion of a vortex core under perturbation. Here, we present a direct imaging study of magnetically soft and hard mesoscopic discs of Permalloy and Cobalt under external field perturbations from equilibrium through annihilation and nucleation. The high resolution magnetic imaging of sub 6nm in Lorentz mode affords detail below critical domain wall features of less than 20nm where the soliton-regime breaks down into transverse Bloch walls far from equilibrium. By holding the ferromagnetic system in an external field we can capture the magnetic configuration far from equilibrium states near annihilation and during the nucleation process. Integrating these experiment with micromagnetic simulations we will describe how differently magnetic vortices can behave under perturbations, which is important when attempting to use them in applications such as logic, memories, and antennas. Work supported by the DOE-BES-MSE,under Contract number DE-AC02-98CH10886 .

Invited Talk: Fundamental Magnetic Interactions in Patterned Nanostructures: Simulation, Fabrication and High-Resolution Microscopy

Thank you to the organizers of  the 2013 MXLS Workshop "New Opportunities for Magnetic Dynamics and Materials at NSLS-II and MAX-IV” for the invited talk.

Fundamental Magnetic Interactions in Patterned Nanostructures: Simulation, Fabrication and High-Resolution Microscopy

Through the use of complimentary multi-technique experimental approaches, investigations of fundamental magnetic interactions, such as magnetostatic, direct exchange, and indirect exchange, in nanomagnetic structures perturbed by static and high frequency excitation, are presented.

Suggestions of using dipolar coupled single domain patterned nanomagnets for applications such as logic, has demonstrated the potential for low-power room temperature operation. The fundamental evolution of reaching desired states can be described as an energy minimization process, where elements exhibit preferential magnetization axes due to engineered shape anisotropies, and local energy minima are reached utilizing external stimuli and strong magnetostatic interactions. Magnetic Force Microscopy (MFM) was implemented in conjunction with NIST’s micromagnetic framework OOMMF, in order to detail the energies associated with different local ground states of coupled nanomangets. The kink energy and magnetic frustrations in ferromagnetic and anti-ferromagnetic ordered elements in various directional applied fields will also be discussed.

Dipolar interactions produce long range force fields but stronger yet are the quantum mechanical short range exchange interactions of neighboring spins. The competing energies of exchange interactions in domain walls and magnetic flux due to surface charges at boundaries can lead to interesting topological charges in room temperature nanomagnetic systems. In a properly engineered nanodisk, magnetic vortices appear, with two degrees of freedom (chirality and polarity), four degenerate states, and exhibit radial symmetry at equilibrium. Utilizing ferromagnetic resonance, transmission electron microscopy, and x-ray transmission microscopy, details of competing direct exchange, demagnetization, indirect exchange energies in magnetic vortex systems are investigated through the observation of core deformation in static fields. The use of high frequency field excitations applied in-situ in TEM to dual vortex core indirect exchange coupled nanodisk heterostructues and the frequency response probed through the time averaged orbital amplitude are also presented. 

APS March Meeting 2013 Talk

I will be presenting our XTM and TEM microscopy work on interlayer exchange couple magnetic vortices under an applied field.

Element Specific Observation of Interlayer Exchange Coupled Dual Vortex Core Nano  Systems

Abstract:

We report on the magnetic evolution of magnetic vortices in nanoscale and multilayer disk structures. The tri-layer structure consists of Co and Permalloy (Py) layers, coupled across a thin (1nm) Cu spacer that provides strong coupling between the Co and Py layers. Element-resolved full-field XMCD microscopy is combined with ultra-high resolution Lorentz transmission electron microscopy, permitting measurement of both layer-resolved domain patterns and the vortex structure averaged across the tri-layer. We examine the evolution of the vortex structure while the nanostructure is cycled through the M-H hysteresis loop. In particular we will discuss the effects of strong interlayer exchanged coupling on a dual vortex core system, including analysis of the layer-resolved coercivity, and the evolution, deformation, annihilation, and nucleation of the vortices.

The figure above shows the domain wall phase diagram measured via Lorentz TEM under quasi-static applied fields.

APS March Meeting 2012 Talk

I will be presenting our work entitled:

 High Frequency Excitation of Nanometer-Scale, Strongly Coupled FM / NM / FM Disks 

Abstract:
There is great interest in the manipulation of magnetic domains in nanostructures from both a fundamental and applications perspective. In particular, the use of resonant frequency excitations permits a power reduction of the driving forces necessary to induce detectable motion in magnetic vortex structures. Here we present an experimental and numerical study of patterned tri-layered disk stacks which are composed of 25nm Permalloy | 1nm Copper | 15nm Permalloy, excited at resonance, ranging from 250-500nm in radii. In-situ Lorentz microscopy was used to acquire time averaged real space images of the vortices' gyrotropic motion and micromagnetic simulations were implemented to further understand the coupled dynamics between the ferromagnetic layers across the thin non-magnetic spacer layer. We discuss the effects of interlayer coupling on the vortex trajectories and resonant frequencies for the individual ferromagnetic layers.

The figure above shows the gyrotropic motion of a vortex core under a high frequency applied magnetic field.