# Magnetisation, How does sample size and time scale affect this?

I am curious about the how size of a sample influences magnetisation of a material. For example if I have a series of rods of increasing thickness in a magnetic field in air, the thicker rods will be less magnetised than the thinner rods due to there being more material in the sample in the same strength field?

How are magnetisation curves measured in regard to sample size? I am aware that the coercivity will move depending on the size of the material, is this also the case for magnetisation saturation?

I am also wondering about time scale for magnetisation. If I could create an oscillating magnetic field in the hundreds of megahertz, is there a limit to how quickly the magnetisation within the sample could be switched?

Thank you for any help. David

• The purity of the phase transition does depend on the speed with which you are going through the critical point. For a BEC, the characteristic speed is the speed of sound, I would suspect the speed for a magnet would be the speed of magnons - i.e. the collective excitations of spins. The slower you go through the phase transition, the longer the coherence will extend in your magnet. Basically the larger a single domain can become, instead of locally ordered domains that average out to $0$ in the whole sample size. – SuperCiocia Jan 30 '18 at 11:36
• Thank you for your comment SuperCiocia, your explanation is a bit beyond my current knowledge but I think I understand what you are saying. – Dave Feb 1 '18 at 10:42