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 2022, 2019, 2018, 2017, 2015, 2013.

1. - Answered - [Ron Goldfarb] What is the unit for magnetic susceptibility in the cgs and SI systems? Are these quantities the same?
2. - Answered - [Juanjo de Miguel] Schrödinger equation: is the separation of variables an approximation or it is exact?
3. - Answered - [Juanjo de Miguel] Is the Zeeman energy a postulate, or can it be demonstrated from other fundamental laws?
4. - Answered - [Juanjo de Miguel] Why is Cu diamagnetism, whereas it has only 9 electrons to fill the 3d shell, thus the shell is not complete?
5. - Answered - [Juanjo de Miguel] Why Sm is non magnetic as an isolated atom and FM as a solid?
6. - Answered - [Olivier Fruchart] If I have a nanoparticle bigger than 100nm, what would be a good technique to determine effectivy whether a DW has formed? Maybe you have, as an example of nanoparticle with diameter lower than 100nm with a DW width determined by holography TEM or other?
7. - Answer during next lecture - [Juanjo de Miguel] In magnetic multilayers, how do you explain teh effect of induced magnetic moments (from Co for example) on some non-magnetic materials like W, while in other 5d materials it does not occur, like in the case of Au?
8. - Answered - [Oscar Iglesias] How to distinguish the different origins of anisotropy? For example, in a thin film how to distinguish between IP shape anisotropy and crystal anisotropy?
9. - Answered - [Oscar Iglesias] How can we relate the spin-orbit coupling to magnetostriction or to single-ion anisotropy?
10. - Answered - [Oscar Iglesias] It is known that FeO is an antiferromagnetic material, but it is also said that in practice is is often found as Fe_1-xO. What is then the order: AFM or ferrimagnetic?
11. - Answered - [Olivier Fruchart] Regarding exchange bias, given the fact that we have a system formed of an AFM and a FM, in the case of core-shell particles, does the definition of blocked regime remains? I feel that it is different from large systems, in which remanence is affect by the existence of domains.
12. - Answered - [Jan Vogel] On slide #62, you showed that the electron temperature increased roughly 10K. Is this a typical change? I always thought it was in the order of 100-1000 K. Or is that the order of magnitude for complete reversal?
13. - Answered - [Jan Vogel] What is a heat penetration depth? Is it the synonym for "diffusion length of the electron"?
14. - Answered - [Jan Vogel] So, the magnetization precession in the large time scale (up to ns) is caused by thermal effect, is that correct? Is it possible to understand solely from the kerr-effect signal that the oscillation are due to the thermal effect? Or one need to measure the reflectivity also?
15. - Answered - [Jan Vogel] You showed that transition of electrons due to the faraday / kerr effect. How does the electronic transition influence the polarization of the photon?
16. - Answered - [Jan Vogel] X-ray resonant magnetic scattering is useful for periodic magnetic materials, in what direction is the periodicity is it horizontal over the surface or can it be periodicity vertically along the depth of the sample?
17. - Answered - [Jan Vogel] In your lecture you showed how X-rays can be used to detect magnons. How can we use optical methods to probe magnon-magnon coupling?
18. - Answered - [Jan Vogel] From the techniques you mentioned, if think you mentioned at some point something related to biology. So, are these techniques applicable to power samples or something different from thin films and nanoparticles?
19. - Answered - [Jan Vogel] Could you please give a short introduction about diff.... (?) yield in XMCD and if we can apply sum rules. As far as I konw we cannot apply sum rules directly to fluorescence yield. Is there any other way to quantify it?
20. - Answered - [Oksana Chubykalo-Fesenko] Are there limitations other than light length when determining domain wall width using Kerr microscopy? Any differences in observing the wall of Nell and Bloch type?
21. - Answered - [Oksana Chubykalo-Fesenko] To which extent can we consider certain magnetization textures as quasiparticles: scattering, tunneling etc.
22. - Answered - [Oksana Chubykalo-Fesenko] Why the size of a skymrion changes uopn channging DMI? Is it better to change the skyrmion size with electric field or magnetic field? I mean, which of them is more convenient?
23. - Answered - [Oksana Chubykalo-Fesenko] Why is moving of skyrmions important, is there any connection between skyrmion stability and its motion? Why do we want stable skyrmions?
24. - Answered - [Claire Donnelly] What is the penetration depth for Kerr. How to observe a domain wall at the interface with a thicker film, say, 40nm?
25. - Answered - [Claire Donnelly] Can we measure experimentally the domain width when in the nm scale?
26. - Answered - [Claire Donnelly] A while ago, our group had the idea to visualize a flight of stairs structure made of glass/ other transparent material. If a laser pulse hits this structure, the pulse will be divided into multiple pulses with different time delays due to the fact that light travels slower through glass than through air. Because now these pulses are separated in time and space, they can be distinguished by the position of the detector. Until now, we have not been able to find someone who is willing/able to make this for us. If anyone has any suggestions, I would love to hear it!
27. - Answered - [Claire Donnelly] For all the imaging techniques, does the direction of magnetic moment matter? For instance, can I measure a sample with only in-plane magnetization with MFM?
28. - Answered - [Stuart Cavill / Olivier Fruchart] How can I calibrate Lakeshore 3600 again if I change the distance between two magnets (coils)? Is it realizable?
29. - Answered - [Olivier Fruchart / Jeff Childress / Bernard Diény] In the lecture, it has been mentioned that exchange bias induces a shift of hysteresis loop. Could you please also introduce the vertical shift which I read is about exchange spring? Is it also exchange bias?
30. - Answered - [Ron Goldfarb] About How to write a scientific paper. It is sad but true that most of the time the experiments that I perform does not give what I am looking for. So, before each what I was originally trying to, I used a lot of resources and time. I can pretend that nothing of that happened and publish as if I knew fro mthe beginning that that was the right way, but I feel, somehow, it is not completly fair for other people to miss the things that didn's work, and let them rediscover them externally since no one is reporting them. Do you think that there is space where those things that did not work but drove you to the right path can be reported. In order to prevent people from wasting their time and try new things.
31. - Answered - [Denys Makarov] What is the limitations of making more multiferroic materials like BiFeO3?
32. - Answered - [Denys Makarov] Why do we need ferromagnetic insulators? What are the fields of application of such materials?
33. - Answered - [Denys Makarov] Why magnetostriction is a bulk effect?
34. - Answered - [Denys Makarov] When we have a new material, how do we know the thermal activation energy at the surface?
35. - Answered - [Denys Makarov] Do you know whether in SPS system an external magnetic field can be applied during the synthesis process?
36. [Alberto Bollero] How seriously do scientists consider the ethics of the sorcing of the raw materials they use in their research? Co is the classic example. In magnetism, it is regularly used, but >70% comes from the democratic republic of Congo where there have been reports of horrendous working conditions including exploitation of child labour. While increased deman may lead to increased investment and better conditions, this seems naive. To what extent should we consider "unavailable" and "unavailable exploitation/modern slavery/child labour" as equivalent? Should we opt for more easily accessible materials at the cost of performance or rate of progress?
37. [Jacobo Santamaria] Say you have a disc of Type-II superconductor at an external external field above Hc1 so that flux has started to penetrate the bulk. What strength of demagnetising field would this experience? Looking at the larger sample, it seems to be a disc with H perpendicular to plane, so, a high N. Looking at only the flux-containing volumes, they are long cylinders with a low N. Does the fact that those are quanta of flux affect their demagnetising nature or the way they might couple together?
38. [Aurélien Manchon] When it comes to SOT switching in HM/AF bilayers, does the inverse spin galvanic effect play any role?