Cooperative Magnetism Flashcards
Where do collective magnetic properties in inorganic solids arise from?
Electron-electron interactions
What does the magnetic dipolar interaction depend on?
The magnitude of the magnetic moments, their relative orientation and their seperation.
The orbital overlap of two paramagnetic ions in a solid gives rise to which two different total spin states ?
How do you work out the exchange constant , Jex
It is the difference in energy between the triplet and singlet state
When is the triplet state energetically favourable?
When is the singlet state energetically favourable?
If two electrons in partially filled orbitals of a magnetic metal ion interact via the same intermediate non-magnetic anion orbital, what is the sign of Jex and what state will be observed?
If two electrons in partially filled orbitals of a magnetic metal ion interact via two orthogonal intermediate non magnetic anion orbitals, what is the sign of Jex and what state will be observed ?
What is a ferromagnet?
A material whose magnetic moments align parallel
What is an antiferromagnet?
A material whose magnetic moments align antiparallel
In ferromagnetic and antiferromagnetic materials, what is observed at high temperatures and why?
A paramagnetic state, as long range magnetic order is disrupted by random thermal fluctuations of magnetic moments. Needs to be cooled below its critical magnetic ordering transition state.
What is the Curie-Weiss law and what extra does it account for ?
What are the respective signs of Weiss constants for ferromagnets and antiferromagnets?
What is a ferrimagnet?
What determines the characteristic Curie temperature (where ordering occurs) of a ferromagnetic material ?
The energy scale of its exchange interactions, theta.
In mean field theory, the internal molecular field felt by an electron is proportional to what?
If we apply a magnetic field to a ferromagnetic material what equation tells us the total field experienced by a given moment?
How do you derive the Curie-Weiss law from mean field theory for a ferromagnet?
From M/H+(lambda)M=C/T
What is a ferromagnets magnetic hysteresis?
The ferromagnets behaviour after the magnetising field has been removed.
What is magnetoresistance?
The change in resistance of a material when a field is applied.
