Lectures 7&8 (Expression for M(T) and Rhodes-Wohlfarth Plot)

Question 1

Why is only J conserved, not L and S?

Answer 1

Weak SOI between L and S can cause pertubation

Question 2

When do we use the equation for µ_eff?

Answer 2

In a many-electron atom

Question 3

Equation for µ_eff?

Answer 3

g µB √ J(J+1)

Question 4

Equation for Lande g-factor?

Answer 4

g = 3/2 + S(S+1)-L(L+1) / 2J(J+1)

Question 5

Why is g ~ 2 not = 2?

Answer 5

Electrons emit and reabsorb virtual photons - giving an extra orbital component

Question 6

Why does calculated µ_eff not match measured µ in 3d ions?

Answer 6

Orbital quenching due to Coulomb interaction with surrounding charges

(3d wavefunctions overlap - orbital moments do not move)

Question 7

What are paramagnetic salts?

Answer 7

3d ions

Question 8

How to fix the fact that µ_eff ≠ µ_measured in paramagnetic salts?

Answer 8

Assume L=0 so µ_eff = 2√S(S+1)

Question 9

In 3d ions, is J mostly due to S or L? Why?

Answer 9

S due to orbital quenching of L

Question 10

What is an application for paramagnetic salts?

Answer 10

Magnetic refrigeration

Question 11

How does magnetic refrigeration work in comparison to normal refrigeration?

Answer 11

Normal - compressed gas takes heat out food

Magnetic - aligns m. moments by applying field. Take heat out (e.g., by liquid nitrogen). Now heat absorbed when messes up µs, with heat being extracted

Question 12

Something about Rhodes-Wolhfarth plot