Materials Chem Magnetism

Magnetism in solids originates from the magnetic properties of an…

electron

Why do electrons exhibit magnetic properties?

electrons have spin

ions where all electrons are paired

diamagnetic ions

why do diamagnetic ions have no net magnetic moment?

magnetic fields of the paired electrons cancel each other out

ions with unpaired electrons and therefore a net magnetic moment

paramagnetic ions

variable S

spin (sum of spin quantum numbers for all electrons in subshell)

variable L

orbital angular momentum (sum of magnetic quantum numbers for all electrons in subshell)

variable J

total momentum

J-value if subshell is less than half-filled

absolute value of L-S

J-value if subshell is more than half-filled

L+S

J-value if subshell is half-filled

S

What is the highest possible value of L in a d-orbital

3

Which value of magnetic moment is sufficient for first row transition metals?

spin-only value

How do you number the orbitals in a d-subshell when calculating L?

+2,+1,0,-1,-2

Where is full treatment of magnetic moment calculation most necessary?

lanthanides

Why do surrounding anions/ligands in transition metal compounds quench the orbital angular momentum?

atomic orbitals are used to make bonds and their spatial orientation is fixed

Spin-orbit coupling increases the magnetic moment for which electron configurations

d6, d7, d8, d9

Spin-orbit coupling decreases the magnetic moment for which electron configurations

d1, d2, d3, d4

variable B

magnetic induction (field strength within the sample region)

variable H

applied magnetic field (field coming from external source)

variable I

magnetization intensity (field originating from the sample)

diamagnetic samples in a magnetic field are…

repulsive (amount of field in the sample area is smaller than applied field)

value of variable I for diamagnetic samples

negative

what happens to variable B for diamagnetic samples

B is lowered

paramagnetic samples in a magnetic field are…

attractive (amount of field in the sample area is greater than applied field)

value of variable I for paramagnetic samples

positive

What happens to variable B for paramagnetic samples

B is raised

When does B=H

when a magnetic field is applied to no sample

What is given by B/H

permeability 

What is given by I/H

magnetic susceptibility

all magnetic moments are aligned

ferromagnetic

magnetic moments are alternating in alignment (cancel out)

antiferromagnetic

magnetic moments are alternating in alignment but there are two different ion types so the overall moment is not completely canceled

ferrimagnetic

When magnetic susceptibility is measured at different temperatures, paramagnetic substances with localized, weakly interacting electrons obey the…

Curie-Weiss law

what is the slope of a curie-weiss plot for a paramagnetic material

1/C where C is the Curie constant

What is the x-intercept of a Curie-Weiss plot for a paramagnetic material

theta (Weiss constant) (also equal to temperature in kelvin at this point)

What type of information is given by the sign of the Weiss constant?

short range magnetic interactions

material is completely paramagnetic (magnetic moments are independent of each other and do not interact)

when theta=0

magnetic moments have some ferromagnetic interactions with each other (no long range order)

when theta>0

magnetic moments have some antiferromagnetic interactions with each other (no long-range order)

when theta<0

temperature below which long-range magnetic order occurs

magnetic transition temperature

magnetic susceptibility measurements are performed by…

applying a constant magnetic field to the material while changing the temperature

lowering temperature has what effect on magnetic susceptibility for ferromagnetic materials?

increases magnetic susceptibility 

In a ferromagnet the Curie-Weiss law is only obeyed when

temperature is greater than or equal to 3x the magnetic transition temperature 

soft vs hard ferromagnetic materials are determined by

holding a constant temperature and changing the strength of the applied magnetic field

materials that can generate large magnetization when placed in an external magnetic field but the magnetizations readily goes back to zero upon removal of external magnetic field

soft ferromagnetic materials

materials that retain their strong magnetization even when the external magnetic field is removed

hard ferromagnetic materials

for antiferromagnetic materials, as temperature decreases there is a sudden _____ in susceptibility at the magnetic transition temperature

decrease

occur due to an overlap of wavefunctions (atoms are very close)

direct exchange magnetic interactions

occur through spin polarization in conduction electrons (atoms are relatively distant)

indirect exchange magnetic interactions

occur through semi-covalent interactions with orbitals of intermediate ion (atoms are too far apart)

superexchange magnetic interactions

what type of interactions occur between eg orbitals and the p orbital

sigma

what type of interactions occur between t2g orbitals and the p orbital

pi

what type of values do diamagnetic compounds have for magnetic susceptibility?

negative values