Researchers Study Behavior of Ferromagnetic Particles using Computer Simulations

This summer, Jennifer Coulter worked on modeling the behavior of ferromagnetic particles with Alfredo Alexander-Katz, the Walter Henry Gale Associate Professor of Materials Science and Engineering at MIT. The image on the computer background shows a map of the path traveled by individual active particles as they spin through a passive matrix, with colors denoting particle location at different times. (Photo: Denis Paiste/Materials Processing Center)

During the course of this year, MIT Associate Professor Alfredo Alexander-Katz’s team demonstrated experimentally that ferromagnetic particles spinning under a rotating magnetic field in a milky suspension are attracted to each other across comparatively long distances in a mass of non-magnetic particles.

Materials Processing Center (MPC)-Center for Materials Science and Engineering (CMSE) Summer Scholar Jennifer Coulter interned with Alexander-Katz, the Walter Henry Gale Associate Professor of Materials Science and Engineering at MIT on a project to create a more universal computer model for these active spinning particles in a passive colloidal mix.

We’re studying the interactions of the spinners with the passive particles through simulation.

Jennifer Coulter, Summer Scholar, MIT

Illustrating this theoretical environment, Coulter explains, “Only the spinners move.” During the simulation, the non-magnetic particles are in fixed pattern without moving.

The Power of Soft

This project is applicable to the Alexander-Katz lab’s research on a broad range of active soft-matter challenges, which include understanding the way neurotransmitters move from one neuron to another in the brain, and how single-celled organisms sense each other at a distance.

“The power of soft means [that] with very small stimuli we can actually have large or strong changes,” said Alexander-Katz, a member of the Physics of Living Systems group, during a presentation to Summer Scholars in June.

For Coulter, a rising senior at Rutgers University whose previous research deals with high-energy physics, biophysics is new territory.

The way I’ve been working with him on this project has been an experience in using what I know in terms of computing and general physics knowledge to develop and explore a new system. I’ve actually found that a lot of the work I did in high-energy physics has been really useful because that’s also computational, even though it’s very different. So I had some skills coming in, but I’ve definitely had some time to work on them here. I’m running larger-scale things, where I have to deal with huge numbers and lots of data, so I need to consider things in Unix command lines. I’m using different computers to run my code, because I can’t run it on my laptop. It would overheat or take days.

Jennifer Coulter, Summer Scholar, MIT

She is writing most of the code for this by herself using Python and an assortment of Unix tools including Shell and Bash scripts.

Graduate Level Skills

“I think that in terms of just general computing stuff, in Unix and other things, it’s been really good to spend more time working on that, because those are skills I hope to use in grad school. I’d like to go for computational physics, probably,” Coulter says.

With the aid of this computer model, Coulter tested how alterations in simulation specifications impact the end result. For instance, she could modify the rotational speed of the magnetic field, alter the torque from hydrodynamic interactions, and change the attractive or repulsive force between passive particles and spinners.

“The key thing that we’re going to vary is a parameter that’s going to help us describe the disorder of the way we’ve arranged the passive particles; so we want to study how disorder affects the transport of the spinners through the passive particles,” Coulter says. The simulations cover a range from a very ordered system through a range of varied distortions to the ordered system to observe how spinners react as disorder grows.

Video Credit: Massachusetts Institute of Technology (MIT)/

MIT scientists including Associate Professor Alfredo Alexander-Katz have found a new kind of long-range interaction between particles, in a liquid medium, that is based entirely on their motions. (Video: Melanie Gonick/MIT)

She is keen on learning what conditions cause spinners to move in a straight line versus a diffuse pattern (spread in various directions).

“I think it would be cool if we could see really diffusive transport in relation to adding disorder to our system,” Coulter says. “The end goal is to compare the active matter system to a system that’s currently very popular in terms of topological materials and 2D materials and transport in those materials. So we would like to try to create this system as an analogue to that more difficult to study system.”

think in terms of my personal growth, actually the best part of my experience here has been just working with Prof. Alexander-Katz. It’s really nice to be able to talk to him for an hour or more at a time, several times a week. He’s really supported me and gives really good feedback, and I think in terms of my development as a scientist, a lot of what I’ve gained from this has just been in my experience working with him. I really appreciate his role as a mentor.

Jennifer Coulter, Summer Scholar, MIT

Her project’s success would depend on being able to characterize the disorder of the arrangement of passive particles, and how it alters the nature of transport for the spinners, Coulter suggests. “It’s actually, I think, something we’re pretty close to attaining, but since it was a smaller project, we are now starting to do some more final runs of the code. I’m about to get some of the last results soon ... so hopefully they’re the good kind. They’ve looked really promising up to this point.”

‪‪MPC‬‬‬‬‬‪‬‬‬‬‬‬‬‬‬‬‬‬ and ‪CMSE‬‬‬‬‬‬ sponsor the nine-week National Science Foundation (NSF) Research Experience for Undergraduates internships with support from ‪NSF‬‬‬‬‬‬’s Materials Research Science and Engineering Centers program.‬ The program was conducted from June 7 to August. 6.‬‬‬‬


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