LC Cooperative Magnetism in Solid State Flashcards
what are the 2 different total spin states
triplet and singet
what is Stot in the singlet state
0
what is Stot in the triplet state
1
what is the formula for Jex
Jex = (Es - Et) / 2
when is Es favoured
Jex > 0
when is Et favoured
Jex < 0
when is Et generally favoured
when 2 electrons are in the same atom
when is Es generally favoured
when 2 electrons are in different atoms
`what is super exchange
where 2p orbitals can transmit the exchange between unpaired electrons in 3d orbitals
when governs the energy of a super exchange interaction
degree of orbital overlap
what rules determine the sign of J
Goodenough- kanamori rules
what state forms from 180 degree interaction on the same orbital and what sign is J
singlet Jex < 0
what state forms from orthogonal overlap of 2 orbitals and what sign is Jex
triplet Jex > 0
what happens to magnetic moments in a ferromagnet
allign parellel
what happens to magnetic moments in a antiferromagnet
allign anti parellel
when does a material become ferromagnetic/antiferromagnetic
below a critical temperature - above this temp it is paramagnetic
what is the curie wiess law formula
Xm = C / (T- theta)
what does the wiess constant represent
reflects the energy scale of magnetic interactions in a material
what is the sign of the wiess constant in an antiferromagnet
-
what is the sign of the wiess constant in a
ferromagnet
+
what is a ferrimagnet
an antiferromagnet where the opposing moments dont cancel out do it acts like a weak ferromagnet
what is the value of Tc similar to
the weiss constant
whatis the basis of mean field theory
electron interactions are modelled by internal molecular field, Hm
what is Hm equal to
lamda M
what does mean field theory predict
magnetic susceptiblity will diverge at Tc
what is a ferromagnetic domain
an individual part of a material where moments are alligned together
what is magnetoresistance
when resistance changes
what effect does doping perovskites have on exchange
LaMnO3 doped with Sr2+ oxidised Mn3+ to Mn4+ - becomes ferromagnetic as e can move
what temperature does antiferromagnetic ordering occur
neel temperature (TN)
what is TN equal to
|wiess constant|
what sign is the molecular field of an antiferromagnet
-ve
how does sublattice a compare to sublattice b
equal in magntitude opposite in direction
what is the formula for braggs law
nlambda = 2dhkl sin(theta)
which superexchange is dominant in MnO
pi 180 superexchange shown by powder diffraction
what is the (anti)ferromagnetic state of manganite perovskites
contains layers of ferromagnetism by superexchange with an antiferromagnetic structure
what is a magnetisation curve like in a ferrimagnet
does not vary smoothly with T
has a compensation point
what is a compensation point
where the magnetisation on each sublattice exactly cancelled
give an example of an inorganic ferrimagnet and its structure
MFe2O4 M = divalent
cubic spinel
state the magnetic properties of a spinel structure
M is diamagnetic
overall compound is paramagnetic
dominant exchange is AFM
give details of inverse spinel magnetisation traits
AFM interactions cause Fe3+ ions cancel
magnetisation is determined by ordering of Mn2+
what is the natural ordering in magnetite
strong superexchange interactions between ions
neighbouring ions interact by double exchange
