Bridging Atomistic to Continuum Scales – Multiscale Investigation of Self-Assembling Magnetic Dots Katsuyo Thornton (University of Michigan Ann Arbor)

Bridging Atomistic to Continuum Scales – Multiscale Investigation of Self-Assembling Magnetic Dots

Katsuyo Thornton (University of Michigan Ann Arbor) DMR 0502737

Funded as a part of the NSF-EC Cooperative Activity in Computational Materials Research program, this grant aims to advance multiscale computational materials science through development of a suite of tools for modeling directed self-assembly of nanoscale magnetic dots. The grant is enabling extensive collaboration of researchers from the US and the EU, including M. Asta (UC Davis), J.S. Lowengrub (UC Irvine), P.W. Voorhees (Northwestern), A. Voigt (CAESAR, Germany), T. Ala-Nissilä (HUT, Finland), O. Fruchart (CNRS, France), M. Kotrla (ASCR, Czech Republic) and the PI, to achieve this goal. Shown on the right are examples of collaborative work supported by the grant, which spans from ab initio density functional theory to phase-field crystal modeling to continuum-level micromechanical calculations.

Top: Shear stress originating from one period of interfacial misfit dislocation, based on the quantum mechanical calculation result (left). The dislocation line lies at the origin out of the figure plane.

Left: Quantum mechanical calculation of Fe film on Mo(110). The spin-density difference is shown.

Bottom: Phase-field crystal simulation of heteroepitaxy shows dislocation formation (noted by a circle).



One of the notable phenomena observed in heteroepitaxial magnetic systems such as Fe/Mo or Fe/W is the existence of magic height or metastable film height observed during film growth. The discovery of the metastable height allows fabrication of thicker, self-organized nanowires, which could potentially yield more magnetically stable recording media.

We investigated the effect of misfit dislocation on the film morphology by combining the stacking fault energy calculated from first principles with a continuum Peierls-Nabarro model. We observed from equilibrium calculations a tendency to exhibit a preferential height at a particular misfit dislocation spacing. This non-monotonic behavior could potentially explain the origin of the metastable height.

Preferential Height

Total dislocation energy per film (Fe) atom at different film thickness and dislocation spacing with units of atomic layer (AL).

Total energy per film atom at dislocation spacing of 22 substrate interplanar spacings.

First principles calculation of a Fe film on Mo(100). (M. Asta)



Broader Impacts

- The grant supports undergraduate and graduate students and postdoctoral fellows to pursue education and training in interdisciplinary science in an international team.

- The PIs host a four-week course taught as a part of the California State Summer School for Mathematics and Science (COSMOS) that utilizes computational tools in teaching high school students about crystal growth. This year, thirteen female students as well as five male students participated in the course.

- Outreach activities are held to broaden interest in materials research. For example, the PI held workshops during Engineering Camp-In at the Ann Arbor Hands-On Museum, during which sixty boy scouts learned about about engineering and materials science.

Engineering Camp-In at Hands-On MuseumEngineering Camp-In at Hands-On Museum

COSMOS for high school students (with J. Lowengrub)

COSMOS for high school students (with J. Lowengrub)

Documents

Bridging Atomistic to Continuum Scales – Multiscale Investigation of Self-Assembling Magnetic Dots Katsuyo Thornton (University of Michigan Ann Arbor)