Question
Magnetic dipole-dipole interactions are too weak to explain certain magnetic phenomena, which are instead caused by electronic interactions. For 10 points each:
[10m] Electron-electron repulsion energies are reduced when spins are aligned due to this effect, as they avoid each other. This effect corresponds to the ‘Fock’ term in the Hartree-Fock method.
ANSWER: exchange [accept exchange interaction, accept exchange energy, prompt on Pauli Exclusion with ‘what is the name of the energy associated with that’]
[10h] Conductors have a spontaneous magnetic moment when this condition is satisfied and the susceptibility diverges. This effect depends on the density of states at the Fermi level multiplied by the exchange energy.
ANSWER: Stoner Criterion
[10e] The Stoner Criterion applies to the itinerant type of this phenomenon, where alignment of spins cause materials like iron to have a spontaneous magnetic moment.
ANSWER: ferromagnetism [prompt on magnetism; do not accept or prompt on antiferromagnetism]