5.1 Magnetism - The Basics

Question 1

How can magnetism be thought of in a classical sense?

Answer 1

Arises due to magnetic moments from current loops

Question 2

What direction is the magnetic field when compared to the current loop?

Answer 2

Perpendicular - RH Rule

Question 3

How can we get the total magnetisation of a material?

Answer 3

Measure the total magnetic moment per unit volume over a large scale, so variations aren’t seen

Question 4

What is the magnetic susceptability?

Answer 4

A dimensionless quantity which is a measure of how much a material will become magnetised when a B field is applied

Question 5

What defines a paramagnet?

Answer 5

• χ > 0

- Magnetisation is in the same direction as the magnetic field

Question 6

What defines a diamagnet?

Answer 6

• χ < 0

- Magnetisation is in the opposite direction as the magnetic field

Question 7

What defines a ferromagnet?

Answer 7

Magnetisation can be non zero even when no external magnetic field is applied

Question 8

State Hund’s First Rule

Answer 8

Electrons will try and arrange themselves in such a way that they align their spins

Question 9

State Hund’s Second Rule

Answer 9

Electrons will try and maximise their orbital angular momentum L

Question 10

State Hund’s Third Rule

Answer 10

J = | L ± S |

Question 11

Describe the three terms for the new Hamiltonian for an atom in a B field

Answer 11

Have H_0

• Paramagnetic term which looks at the coupling of the B field to the orbital and spin momenta of the electron which align when the B field is applied
• Diamagnetic term which gives an increase in energy as B is increased (opposite to the paramagnetic term)