Atomistic approaches on 2D magnetic materials

  • Dina Abdulwahab

Student thesis: Doctoral ThesisDoctor of Philosophy


The discovery of magnetism in two dimensional materials, first found in CrI3 and Cr2Ge2Te6, has opened up many possibilities to explore, concerning novel phenomena and potential applications in spintronics. Prior to these discoveries, it was thought that magnetism in two dimensions was impossible due to the conditions of the Mermin-Wagner theorem. In this work, the ferromagnet CrI3 is examined in the monolayer to understand how its magnetism may be utilised, potentially in racetrack memory. Ab initio methods provides a way to study CrI3’s nature by calculating individual exchange values and using them to find an appropriate spin model. In the initial literature, CrI3 was identified as an Ising magnet based on experimental data. By using a Monte Carlo atomistic simulation approach, the Curie temperature (TC) of the material can be calculated. Thus, the suitability of the Ising model can be assessed. The atomistic spin model shows that the Ising model overestimates the TC, and we show that by using a modified Heisenberg model, a value of TC much closer to experiment can be calculated. Using this model and our calculated exchange parameters, the spin dynamics in monolayer CrI3 can be examined with the Landau-Lifshitz-Gilbert equation. Spins in monolayer CrI3 appear to fluctuate in zero-field cooling simulations, seemingly as a result of the system’s high anisotropy. Zero-field cooling simulations are also performed on bulk CrI3 revealing a multi-step transition in the material. To consider CrI3’s potential in domain wall motion based technology, simulations of a moving domain wall are carried out on a short section of nanowire to assess domain wall motion under applied field and with the use of a spin-transfer torque, applied current. High velocities of 1020 m/s are reached under applied current. At this point the material undergoes a Walker breakdown collapse of the domain wall, so the limits of CrI3 domain wall motion capabilities are shown.
Date of AwardDec 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorMyrta Grüning (Supervisor) & David Wilkins (Supervisor)

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