Exchange interaction Ferromagnetism

when 2 nearby atoms have unpaired electrons, whether electron spins parallel or antiparallel affects whether electrons can share same orbit result of quantum mechanical effect called exchange interaction. in turn affects electron location , coulomb (electrostatic) interaction , energy difference between these states.

the exchange interaction related pauli exclusion principle, says 2 electrons same spin cannot in same spatial state (orbital). consequence of spin-statistics theorem , electrons fermions. therefore, under conditions, when orbitals of unpaired outer valence electrons adjacent atoms overlap, distributions of electric charge in space farther apart when electrons have parallel spins when have opposite spins. reduces electrostatic energy of electrons when spins parallel compared energy when spins anti-parallel, parallel-spin state more stable. in simple terms, electrons, repel 1 another, can move further apart aligning spins, spins of these electrons tend line up. difference in energy called exchange energy.

this energy difference can orders of magnitude larger energy differences associated magnetic dipole-dipole interaction due dipole orientation, tends align dipoles antiparallel. in doped semiconductor oxides rkky interactions have been shown bring periodic longer-range magnetic interactions, phenomenon of significance in study of spintronic materials.

the materials in exchange interaction stronger competing dipole-dipole interaction called magnetic materials. instance, in iron (fe) exchange force 1000 times stronger dipole interaction. therefore, below curie temperature virtually of dipoles in ferromagnetic material aligned. in addition ferromagnetism, exchange interaction responsible other types of spontaneous ordering of atomic magnetic moments occurring in magnetic solids, antiferromagnetism , ferrimagnetism.

there different exchange interaction mechanisms create magnetism in different ferromagnetic, ferrimagnetic, , antiferromagnetic substances. these mechanisms include direct exchange, rkky exchange, double exchange, , superexchange.