Can Spins Flip in an EPR Experiment?

[Albex]

hello

I got al little bit confused about spins flipping in an EPR experiment. As far as I know, the idea of EPR is to measure the absorption of an electromagnetic wave induced by spin flips if the energy is conserved by
\hbar \omega = g_{spin} \mu_B B_0.
But now I heard several times that a spin cannot be flipped by an electromagnetic dipole field and only optical transitions that include
\Delta m_s = 0
are permitted if there is zeeman splitting.
So how do spins flip then?

Thank you for all answers!

 

[nbo10]

check out Stephen Bundell book, "Magnetism in condensed matter". It has a good discussing on ESR.