The Exchange Interaction

An introduction to the quantum mechanical exchange interaction. Using the example of the first excited state of the He atom, with one electron in the 1s orbital and one electron in the 2s orbital, we show that the energy is lower when the two electrons have their spins parallel to each other than when they are anti-parallel. The energy difference is given by a part of the electron-electron interaction that is called the exchange energy, and has no classical analogue.

[@ashcharya27]

My Prof. had suggested your book, and now accidentally I found your channel. Both are amazing and exciting.

[@augustineokekeoma1750]

Hello Ma. Thank you so much. Your book is amazingly lucid, as lucid as your teaching style. Some people are born teachers.

[@arghyadipojha5917]

thank God! I am so an admirer of your works! To be able to get a lecture from the person leading in the field of magnetic materials is an honour for me, and that to when I'm desperately searching for explanation just few days before semester exam!😅 earlier I had a thought on how impurities might affect these properties like magnetism. Maybe I have to read more, but thanks a lot Ma'am for such free services. This world needs teachers like you.

[@alekseiegorov9857]

Amazing explanation! Thank you, Prof. Spaldin!

[@sarsedacn]

very clear and straightforward lecture. Thanks

[@tongshuanghuang5479]

Thank you for your excellent video. It is a very clear explanation. Yet I still have a question. I want to ask about the total magnetic moment of parallel and anti-parallel spins. The explanation about the total magnetic moment is from 1:20 to 1:30 in the video. The electron circling the nucleus also brings a magnetic moment in the system, called the orbital magnetic moment. However, it seems like you did not take that into consideration. May I know the reason for ignoring it?

[@MrMembury]

This was very informative, thank you! I've been trying to learn more about magnetism and this principle seems fundamental to the modern understanding of it. I'm still worried it would be possible for J to be negative, leading to the antiparallel spins having the lower energy, so clearly I still have some work to do understanding the maths. Thanks again!

[@nicolaspaldin2446]

I'm glad you find it useful Richard. Easier than wading through the maths, you can make an analogy with the Coulomb repulsion between two electrons which always has positive sign...

[@yisehakg5039]

Really beautiful!! Thank you so much.

[@shaikmateen7282]

C2H4 , C2H2 , C3H4 , C2H6 : which of them will do exchange interaction and while will do addition interaction ? Please sir answer.

[@physicswithrasmiranjan9930]

Hi , I think you have written this book Fundamentals and Applications by Nicola A. Spaldin..It is really a nice book.. please upload more videos 🙌🙌

[@MrTroll-wr3kd]

Well done!

[@xcski123]

Where do the negative terms go when expanding from the second equation to the third, fully expanded equation?

[@haya4895]

brilliant

[@Yan_Alkovic]

Oh wow, this is a very recent video, didn't expect that. This is a really great video you've got here! It's nice to see a video on these advanced quantum mechanical topics that _isn't_ plagued by terrible accents. Are you making these videos for a class that you're teaching, or just cause you want to? Either way, I hope you'll keep it going!

[@nicolaspaldin2446]

Dear Yan, Thanks for your kind feedback. A bit of both -- the students in my current class are the first guinea pigs for the videos...

[@Yan_Alkovic]

@@nicolaspaldin2446 Cool! Well, I sure am glad that you didn't make the videos unlisted! Best wishes to you and your students!

[@kuldeepkargeti1916]

Exchange interaction J2 is -24 K. Can you tell me what is this unit K for exchange energy

[@nicolaspaldin2446]

Dear Kuldeep, It's kelvin. Here's a handy units converter if kelvins aren't your favourite: physics.nist.gov/cuu/Constants/energy.html

[@kuldeepkargeti1916]

@@nicolaspaldin2446is it not the exchange costant K. I am confused now. Because exchange energy is [K×n×(n-1)]÷2.

[@nicolaspaldin2446]

Oh, sorry I mis-read your question -- I thought you were asking about how "K" as in kelvin can be used as a unit of energy. In the derivation in this video, in fact K is used to label the Coulomb energy, it's not the exchange energy here.

[@kuldeepkargeti1916]

I was asking a random question, not related to this video. In a paper i saw exchange interaction between two Cr atoms is -24 K. So, this i wanted to know, is it -24 Kelvin or -24 times K. if it is kelvin so is it fine to say that exchange interaction between Cr atoms is minus twenty four Kelvin. Doesn't it seem odd, exchange in Kelvin.