14 Questions
What is a key difference between domain walls in ferromagnets and ferroelectrics?
Domain walls are wider in ferromagnets.
What is the initial state of the magnetisation in a demagnetised sample?
M = 0 and H = 0
What is the direction of the magnetisation in the domains initially?
Aligned along easy axes of the material
What happens to the magnetisation domains when a small magnetic field is applied?
Domains aligned with the applied field grow.
What is the shape of the curve depicting the dependence of magnetisation on the applied magnetic field?
Hysteresis loop
What is the process by which the magnetisation increases with the applied field?
Domain wall motion
At what point in the hysteresis loop does the magnetisation undergo a rapid increase?
Point 2
What happens to the magnetisation when the magnetic field is removed?
It returns to its initial state.
Why is the second regime of magnetization irreversible?
Because the domain wall motion is pinned by defects in the material
What happens to the magnetization when the magnetic field strength is increased?
It increases
What is the direction of the magnetization at Point 3 in Fig. 2.13?
Parallel to the easy axis
What is the resulting magnetization called when the magnetic field strength is further increased?
Saturation magnetization
Why does the magnetization direction rotate away from an easy axis at high magnetic field strengths?
Because the magnetization points exactly parallel to the applied field
How does the magnetization of a ferromagnet differ from the polarisation of a ferroelectric?
The ferromagnet's magnetization is constrained along easy axes
Study Notes
Domain Walls
- Domain walls in ferromagnets are wider compared to those in ferroelectrics
- Domain walls in ferroelectrics are significantly narrower due to polarisation being strongly constrained to point along crystallographic polar axes
Hysteresis Loop
- A hysteresis loop appears when the magnetisation direction is reversed in real ferromagnetic materials
- The curve of magnetisation M vs applied magnetic field H resembles that of ferroelectrics, but with some differences
Magnetisation Reversal
- The reversal of magnetisation direction in ferromagnets can be characterised by the dependence of M on H
- The magnetisation starts at M = 0, H = 0, with domains pointing in different directions
- Upon applying a small magnetic field, magnetisation increases linearly, with domains aligned with the applied field growing at the expense of others
- This process is reversible if the field is removed
Domain Wall Motion
- With increasing magnetic field strength, aligned domains continue to grow, and magnetisation undergoes a rapid increase
- This process is irreversible due to domain wall motion being pinned by defects in the material
- Magnetisation largely points along easy axes, even if the applied field is not exactly parallel to an easy axis
Magnetisation Saturation
- Further increasing the magnetic field strength leads to a further increase in magnetisation, driven by the sweeping of aligned domains through the material
- Magnetisation eventually points exactly parallel with the applied field, resulting in the saturation magnetisation Msaturation
Learn about the importance of exchange interaction and magnetocrystalline anisotropy in materials and how they relate to domain walls in ferromagnets and ferroelectrics.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
