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Antiferromagnetic spin waves 
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#1
Apr1110, 08:00 PM

P: 63

Hey,
can anyone point me to some useful reading material on the semiclassical treatment of spin waves for the antiferromagnetic case? Thanks. 


#2
Apr1210, 02:07 AM

Sci Advisor
P: 3,564

P W Anderson, Concepts in solids, World Scientific, Singapore, 1997



#3
Apr1810, 01:22 AM

P: 483

great book... though not quite sure whether it treats spin waves semiclassically.. edit: in fact I just checked it and the treatment is completely quantummechanical. 


#4
Apr1810, 01:51 AM

P: 981

Antiferromagnetic spin waves
Can you treat spinwaves in AF semiclassically? I seem to think that you don't get a reasonable limit as the spin S > infinity  it oscillates in behaviour on S being a halfinteger and S being integer. (And that's ignoring possible lattice frustration.)



#5
Apr1810, 09:51 PM

P: 483

Yes, you can.
Just like you can semiclassically treat, phonons, electrons, etc.. you can treat "magnons" semiclasically too. Semiclassical,in this context, means an input from quantum mechanics (like dispersion relations, density of states, or effective mass which more or less give equivalent information) accompanied with classical dynamics equations. 


#6
Apr1910, 01:48 AM

P: 981

No, I mean does it make for a good approximation (of course you *can* always just postulate a classical particle + corrections). Certainly in 1D spin1/2 AF do not have spin waves as an elementary particle, since the spinon and holons are deconfined; in this case, I would say that a semiclassical treatment of spinwaves is not appropriate. Usually, in the ferromagnetic case, things are justified because S>infinity is a well defined limit in which we really do get spin waves, and we can argue for a 1/S expansion, in which case the leading order corrections can be seen as interactions. In the AF case, this can not be done analogously.



#7
Apr1910, 01:56 AM

Sci Advisor
P: 3,564

sokrates, I had a look at my copy again. Methinks that Anderson uses in the last chapter "antiferromagnetism and broken symmetry" basically a semiclassical approximation, especially the decoupling of the equation of motion, where he replaces the cross product of spin operators by their mean values, neglecting quantum fluctuations is a semiclassical argumentation.



#8
Apr1910, 12:22 PM

P: 483

Just wondering, is Anderson, himself, saying it's a semiclassical treatment? 


#9
Apr1910, 12:24 PM

P: 483




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