Questions

The purpose of a research School is to provide young scientists the basics in a working field. With this respect interactivity between students and lecturers should be promoted. Thus a key aspect of ESM is the possibility to raise questions during the course of the lectures, interrupting the lecturer. Questions can also be posted anonymously in 'question boxes'. Special sessions for answering these questions are organized, typically 1h every day or two days, during which the lecturers or voluntary students present in more detail issues raised by the students during the lectures or anonymously through a question-box. Questions raised and explained in 2023 are listed below. See also the questions raised in 2023, 2022, 2019, 2018, 2017, 2015, 2013.

• - Answered - [Aires] I was just wondering about the different SOC effects and If one can say clearly something like: Symmetry independent SOC leads to anisotropy and Rashba with broken inversion symmetry leads to DMI and Chiral Chiral interactions stems from (another effect xD) etc. . Or are all the SOC caused interactions induced by a combination of every present SOC effect of my material. I'm not super deep into different SOC effects, so I'm Just wondering :DDD

1. - Answered - [Aires] I'm in general not certain, what different "SOC effects" are. Like how its often done, if one treats SOC with a perturbative approach in DFT. Are the different effects result from crystal symmetry or do they stem from different perturbation hamiltonians or is the naming more phenomenological. I guess one can not say such a general statement, but dunno
2. - Answered - [R. Evans] How do we calculate magnetization when we measure on samples of irregular shape?
3. - Answered - [J. Staunton]
   • CONTEXT: Computationally, estimations of the J magnetic coupling between T and S states (2-spins involved) can be calculated using Noodleman’s and/or Yamaguchi’s solutions to the Heisenberg Hamiltonian (via UDFT calculations and broken-symmetry BS states). The main difference is that Yamaguchi’s solutions are generally more accurate, as they may correct the so-called spin-contamination error, particularly in BS-Sstates.
   • QUESTION: What is the exact definition of spin contamination? Is it related to the through-space spin interactions between overlapping electrons, specifically the overlap between
     a and b electrons involved in the H=−2Jab⋅Sa ⋅Sb operator? In which types of systems might this effect be significant enough to warrant choosing one solution over the other? Are there some generalized characteristics of the electronic structures that indicate a high level of spin contamination?
   • ANSWER:
4. Answered - [B. Hillebrands] From what I understand, spin wave can also be excited by DC spin polarized current, and with perpendicular magnetic anisotropy, spin wave is supposed to propagate in PMA thin film by STT without external field. However, nearly no paper demonstrates I would like to know the possible limitation.
5. Answered - [Kimel] For antiferromagnet, is it possible to induced determinstric switching for AFM (colinearly switching)? If it could be, what;s the promising way to detect it?
6. Answered - [Stuart Cavill] I measure angle dependent in-plane MOKE. Is there any way to make a statement on Mr/Ms, if it is impossible to saturate the sample in certain directions with the given setup? (Like EA saturates at like 10 mT, HA does not saturate until 200 mT [which is our max for in-plane]). Or: Does it maybe saturate, but faraday effect [which I correct for EA since i there can see saturation] is different dependant on sample angle? (film is flat Fe). its an optical MOKE, I measure longitudinal/transversal
7. Answered - [Stuart Cavill] The microwave field which excites the uniform Kittel mode is not homogeneous across the sample. How problematic is this? Will this increase the linewidth and act as T_2 decoherence?
8. Answered - [Stuart Cavill] Could we do SpinValve devices (TMJ) without isolant layer in it? Like, Ferro-magnet to Ferro-Magnet by mismatching the van der Waals layers? - in the sens h-Bn / Fe_x R R/ Fe_x R R / Substrate
9. - Answered - [R. Evans / B. Dupé] Preconditioning steps in the ultrafast dynamics, Can you explain a little bit more about this steps in the simulations?
10. - Answered - [P. Hasnip] We saw that papers are not neglected when evaluating a candidate for an academic position. Often "quality" is better than "quantity". Quality was defined yesterday as publishing in journals as Science/Nature... However, if one decides to dedicate himself to open science and to publish only through open access publishing platforms of the type free publish/free read (e.g. centre Mersenne in France) does it pose issues for employability? Shouldn't we quit this definition of "quality"?
11. [B. Dupé] CONTEXT: Magnetic models (Heisenberg-like + other terms) extracted from first principles calculations make sense only in the vicinity of the ground state i.e for "small" rotations of the spin. When using the Metropolis algorithm, every trial move involves the rotation of a spin by some angle. Then, the total energy is calculated.

• QUESTION: how can we be sure that the magnetic Hamiltonian still makes sense after so many spin rotations or after big rotations when using the Metropolis algorithm?