Lectures 13&14 (Shape Anisotropy, Domains and DWs) Flashcards
Equation for stray field energy (integral version)?
εm = -µ0/2 ∫H.MdV
Equation for stray field energy (component version)?
εm = -µ0V/2 (DxMx^2 + DyMy^2+DzMz^2)
What can stray field energy also be referred to as?
Magnetostatic energy, shape anisotropy energy
What happens if you have an out of plane H applied to a thin film?
Opposite charges build up on top and bottom of film and large Hd
Where does the 1/2 factor come from in the stray field energy?
Avoid double counting - each dipole contributes as field source and as moment
What is the only shape that can be uniformly magnetised by a uniform field?
Ellipsoids
Is shape anisotropy a real anisotropy?
No, but a demagnetising effect
Value of K for thin film out of plane?
K = 1/2 µ0 M^2 D
Which direction will M lie in a thin film? Why?
In plane as this is the lower energy state
How to derive saturation field?
Energy of SW particle - subs ø=90 (H direction)
∂E/∂theta = 0
Subs theta = 90
Equation for saturation field?
H = 2K / µ0M
Difference between Bloch and Neel walls?
Block walls rotate sideways, Neel forwards/backwards
Where do Bloch walls occur?
Bulk samples and thick films
Where to Neel walls occur?
Thin films
Features of Block vs Neel walls?
Bloch - poles associated with them and a corresponding stray field
Neel - shape anisotropy stronger where they occur, so in-plane rotation is favoured and there is no stray field outside the film
