G o2 in so called invar alloys the magnetostriction

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Unformatted text preview: orbitals ⇒ magnetostriction: change in sample dimensions upon change in magnetization.** * There is also a so-called indirect exchange interaction between next-nearest neighbour magnetic ions that are coupled via a diamagnetic ion, e.g., O2-. ** In so-called invar alloys the magnetostriction effect is used to compensate thermal expantion in a certain temperature range since the magnetization at constant field decreases with increasing temperature. 7-20 A > 0 ⇒ parallel spin orientation in ground state, i.e. ferromagnetism. A<0⇒ antiferromagnetism. Collective exchange of conduction electrons Electrons cannot approach each other too closely (Pauli principle). ⇒ Screening of nuclei less effective. ⇒ Lowering of total energy due to increase in Coulombs interaction with nucley. (corresponds to A > 0 in Heinsenberg model). Spontaneous magnetization strongly temperature dependent ! T > TC : Spontaneous magnetization vanishes and crystal becomes paramagnetic. TC: ferromagnetic Curie temperature T >> TC ⇒ χ= C T ...
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This note was uploaded on 01/19/2010 for the course MATERIALS M504 taught by Professor Adelung during the Spring '02 term at Uni Kiel.

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