LC Cooperative Magnetism in Solid State

Question 1

what are the 2 different total spin states

Answer 1

triplet and singet

Question 2

what is Stot in the singlet state

Answer 2

0

Question 3

what is Stot in the triplet state

Answer 3

1

Question 4

what is the formula for Jex

Answer 4

Jex = (Es - Et) / 2

Question 5

when is Es favoured

Answer 5

Jex > 0

Question 6

when is Et favoured

Answer 6

Jex < 0

Question 7

when is Et generally favoured

Answer 7

when 2 electrons are in the same atom

Question 8

when is Es generally favoured

Answer 8

when 2 electrons are in different atoms

Question 9

`what is super exchange

Answer 9

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

Question 10

when governs the energy of a super exchange interaction

Answer 10

degree of orbital overlap

Question 11

what rules determine the sign of J

Answer 11

Goodenough- kanamori rules

Question 12

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

Answer 12

singlet Jex < 0

Question 13

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

Answer 13

triplet Jex > 0

Question 14

what happens to magnetic moments in a ferromagnet

Answer 14

allign parellel

Question 15

what happens to magnetic moments in a antiferromagnet

Answer 15

allign anti parellel

Question 16

when does a material become ferromagnetic/antiferromagnetic

Answer 16

below a critical temperature - above this temp it is paramagnetic

Question 17

what is the curie wiess law formula

Answer 17

Xm = C / (T- theta)

Question 18

what does the wiess constant represent

Answer 18

reflects the energy scale of magnetic interactions in a material

Question 19

what is the sign of the wiess constant in an antiferromagnet

Answer 19

-

Question 20

what is the sign of the wiess constant in a

ferromagnet

Answer 20

+

Question 21

what is a ferrimagnet

Answer 21

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

Question 22

what is the value of Tc similar to

Answer 22

the weiss constant

Question 23

whatis the basis of mean field theory

Answer 23

electron interactions are modelled by internal molecular field, Hm

Question 24

what is Hm equal to

Answer 24

lamda M

Question 25

what does mean field theory predict

Answer 25

magnetic susceptiblity will diverge at Tc

Question 26

what is a ferromagnetic domain

Answer 26

an individual part of a material where moments are alligned together

Question 27

what is magnetoresistance

Answer 27

when resistance changes

Question 28

what effect does doping perovskites have on exchange

Answer 28

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

Question 29

what temperature does antiferromagnetic ordering occur

Answer 29

neel temperature (TN)

Question 30

what is TN equal to

Answer 30

|wiess constant|

Question 31

what sign is the molecular field of an antiferromagnet

Answer 31

-ve

Question 32

how does sublattice a compare to sublattice b

Answer 32

equal in magntitude opposite in direction

Question 33

what is the formula for braggs law

Answer 33

nlambda = 2dhkl sin(theta)

Question 34

which superexchange is dominant in MnO

Answer 34

pi 180 superexchange shown by powder diffraction

Question 35

what is the (anti)ferromagnetic state of manganite perovskites

Answer 35

contains layers of ferromagnetism by superexchange with an antiferromagnetic structure

Question 36

what is a magnetisation curve like in a ferrimagnet

Answer 36

does not vary smoothly with T | has a compensation point

Question 37

what is a compensation point

Answer 37

where the magnetisation on each sublattice exactly cancelled

Question 38

give an example of an inorganic ferrimagnet and its structure

Answer 38

MFe2O4 M = divalent | cubic spinel

Question 39

state the magnetic properties of a spinel structure

Answer 39

M is diamagnetic overall compound is paramagnetic dominant exchange is AFM

Question 40

give details of inverse spinel magnetisation traits

Answer 40

AFM interactions cause Fe3+ ions cancel | magnetisation is determined by ordering of Mn2+

Question 41

what is the natural ordering in magnetite

Answer 41

strong superexchange interactions between ions | neighbouring ions interact by double exchange