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chem313 > LC Cooperative Magnetism in Solid State > Flashcards

LC Cooperative Magnetism in Solid State Flashcards

1
Q

what are the 2 different total spin states

A

triplet and singet

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2
Q

what is Stot in the singlet state

A

0

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3
Q

what is Stot in the triplet state

A

1

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4
Q

what is the formula for Jex

A

Jex = (Es - Et) / 2

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5
Q

when is Es favoured

A

Jex > 0

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6
Q

when is Et favoured

A

Jex < 0

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7
Q

when is Et generally favoured

A

when 2 electrons are in the same atom

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8
Q

when is Es generally favoured

A

when 2 electrons are in different atoms

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9
Q

`what is super exchange

A

where 2p orbitals can transmit the exchange between unpaired electrons in 3d orbitals

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10
Q

when governs the energy of a super exchange interaction

A

degree of orbital overlap

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11
Q

what rules determine the sign of J

A

Goodenough- kanamori rules

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12
Q

what state forms from 180 degree interaction on the same orbital and what sign is J

A

singlet Jex < 0

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13
Q

what state forms from orthogonal overlap of 2 orbitals and what sign is Jex

A

triplet Jex > 0

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14
Q

what happens to magnetic moments in a ferromagnet

A

allign parellel

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15
Q

what happens to magnetic moments in a antiferromagnet

A

allign anti parellel

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16
Q

when does a material become ferromagnetic/antiferromagnetic

A

below a critical temperature - above this temp it is paramagnetic

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17
Q

what is the curie wiess law formula

A

Xm = C / (T- theta)

18
Q

what does the wiess constant represent

A

reflects the energy scale of magnetic interactions in a material

19
Q

what is the sign of the wiess constant in an antiferromagnet

A

-

20
Q

what is the sign of the wiess constant in a

ferromagnet

A

+

21
Q

what is a ferrimagnet

A

an antiferromagnet where the opposing moments dont cancel out do it acts like a weak ferromagnet

22
Q

what is the value of Tc similar to

A

the weiss constant

23
Q

whatis the basis of mean field theory

A

electron interactions are modelled by internal molecular field, Hm

24
Q

what is Hm equal to

A

lamda M

25
Q

what does mean field theory predict

A

magnetic susceptiblity will diverge at Tc

26
Q

what is a ferromagnetic domain

A

an individual part of a material where moments are alligned together

27
Q

what is magnetoresistance

A

when resistance changes

28
Q

what effect does doping perovskites have on exchange

A

LaMnO3 doped with Sr2+ oxidised Mn3+ to Mn4+ - becomes ferromagnetic as e can move

29
Q

what temperature does antiferromagnetic ordering occur

A

neel temperature (TN)

30
Q

what is TN equal to

A

|wiess constant|

31
Q

what sign is the molecular field of an antiferromagnet

A

-ve

32
Q

how does sublattice a compare to sublattice b

A

equal in magntitude opposite in direction

33
Q

what is the formula for braggs law

A

nlambda = 2dhkl sin(theta)

34
Q

which superexchange is dominant in MnO

A

pi 180 superexchange shown by powder diffraction

35
Q

what is the (anti)ferromagnetic state of manganite perovskites

A

contains layers of ferromagnetism by superexchange with an antiferromagnetic structure

36
Q

what is a magnetisation curve like in a ferrimagnet

A

does not vary smoothly with T

has a compensation point

37
Q

what is a compensation point

A

where the magnetisation on each sublattice exactly cancelled

38
Q

give an example of an inorganic ferrimagnet and its structure

A

MFe2O4 M = divalent

cubic spinel

39
Q

state the magnetic properties of a spinel structure

A

M is diamagnetic
overall compound is paramagnetic
dominant exchange is AFM

40
Q

give details of inverse spinel magnetisation traits

A

AFM interactions cause Fe3+ ions cancel

magnetisation is determined by ordering of Mn2+

41
Q

what is the natural ordering in magnetite

A

strong superexchange interactions between ions

neighbouring ions interact by double exchange

chem313 (5 decks)

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