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https://www.nist.gov/itl/math/acmd-seminar-thermally-activated-transitions-between-micromagnetic-states

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# ACMD Seminar: Thermally Activated Transitions Between Micromagnetic States

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Gabriel D. Chaves-O’FlynnSenior Lecturer at the Institute of Molecular Physics at the Polish Academy of Sciences

Friday, October 14, 2022, 3:00-4:00 EDT (1:00-2:00 MDT)

**A video of this talk is available to NIST staff in the Math channel on NISTube, which is accessible from the NIST internal home page.**

**Abstract:**In this talk I will present methods to identify thermal activation barriers for a variety of micromagnetic systems. I start by summarizing the basics of Kramer’s theory of reaction rates as it applies to micromagnetic systems. According to this theory, the escape rate follows an Arrhenius type law and is strongly dependent on the height of the energy barrier separating metastable states. This barrier corresponds to the energy difference between the transition configuration and the local energy minimum from which the system is attempting to escape. The String Method for the Study of Rare Events is a numerical procedure to find the magnetization configurations that determine these thermally activated transitions. I will introduce this method and give several examples of its application to different ferromagnetic systems: nanorings with in-plane anisotropy, nanodisks with perpendicular anisotropy and different strengths of the Dzyaloshinskii-Moriya interaction. For completeness, I will also present approaches for the analysis of thermal stability in cases where Kramer’s theory is not applicable, which happens when the dynamics are not obtained from gradients of a potential, such as the effects of Spin Transfer Torque. If time permits, I will switch gears and discuss specially patterned ferrimagnetic systems in which regions of opposite effective magnetization can exist without a domain wall between them

**Bio:** Gabriel D. Chaves-O'Flynn received his bachelor's degree at the University of los Andes in Bogotá (Colombia). He taught middle school math for two years in the New York City public school system before enrolling in the graduate Physics program at New York University. His advisors were Andrew D. Kent and Daniel L. Stein. He had a postdoctoral fellowship in New Jersey Institute of Technology and another at New York University. He is currently a Senior Lecturer in the Institute of Molecular Physics at the Polish Academy of Sciences. The majority of his work is about the stability of micromagnetic states against thermal perturbations.

**Host:** Michael Donahue

**Note:**This talk will be recorded to provide access to NIST staff and associates who could not be present to the time of the seminar. The recording will be made available in the Math channel on NISTube, which is accessible only on the NIST internal network. This recording could be released to the public through a Freedom of Information Act (FOIA) request. Do not discuss or visually present any sensitive (CUI/PII/BII) material. Ensure that no inappropriate material or any minors are contained within the background of any recording. (To facilitate this, we request that cameras of attendees are muted except when asking questions.)

**Note:** Visitors from outside NIST must contact Lochi Orr (301) 975-3800; at least 24 hours in advance.

Mathematics and statistics

## Contacts

                -  Michael J. Donahue  michael.donahue@nist.gov      (301) 975-5424   
                -  Zachary Grey  zachary.grey@nist.gov      (303) 497-5920   
                -  Lochi Orr  lochi.orr@nist.gov      (410) 598-6986   

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