ÒSpins
interact in two main ways
Ø Exchange
Interactions
Ø And Dipolar
interactions
ÒShort range
exchange interactions are between nearest
neighbour spins.
ÒThe
Exchange Hamiltonian, Hex = -J Σ Si · Sj,
where
ÒJ
is the exchange coupling strength.
ÒSi and Sj are any nearby spins close to each other.