Why do ferrofluids form peaks in a magnetic field?

[Oomph!]

Hello.

I read that nanoparticles of ferrofluid are ferromagnetic, but they do not retain magnetization, so better is superparamagnetic. So, what is true? Is the particles ferromagnetic or paramagnetic? Why they don't retain magnetization?

Thank you.

 

[Andy Resnick]

The stuff I have (Ferrotec) is a colloidal dispersion of magnetite and is macroscopically paramagnetic, even though the magnetitie particles are ferromagnetic (ferrimagnetic? I don't know enough to say). In any case, the ferrofluid loses it's response when I freeze it.

As best I can tell, the macroscopic paramagnetic behavior is a result of dispersing the ferro- or ferri-magnetic magnetite.

 

[Oomph!]

Thank you very much. And I have one more question. If I drop magnet on ferrofluid, the magnet will wrap to ferrofluid. Is any method how can I it unwrap from ferrofluid?

 

[UltrafastPED]

Thank you very much. And I have one more question. If I drop magnet on ferrofluid, the magnet will wrap to ferrofluid. Is any method how can I it unwrap from ferrofluid?

It's best to keep a surface between a magnet and any magnetic particles, such as a piece of clear plastic. It is often impossible to get everything cleaned up.

Following Andy's hint you could try freezing the magnet; this will not harm the magnet. Then let the magnet sit until it returns to room temperature, and clean it with your favorite solvent.

 

[Oomph!]

Ok, so better is not try drop magnet to ferrofluid, yeah? :D

Ferrofluid in magnetic field forms peaks. I read that it is the best variant to the lowest energy of magnetic energy and all system (but not for surface tension). So, it is nice, but I still don't understand to much. So, I think that you know about ferrofluid a lot, so I want to ask you: why the ferrofluid makes peaks? why the particles don't go near to magnet and stay there? it can be better for energy.

 

[UltrafastPED]

Ferrofluid in magnetic field forms peaks. I read that it is the best variant to the lowest energy of magnetic energy and all system (but not for surface tension). So, it is nice, but I still don't understand to much. So, I think that you know about ferrofluid a lot, so I want to ask you: why the ferrofluid makes peaks? why the particles don't go near to magnet and stay there? it can be better for energy.

I worked in a group that was using ferrofluids as part of a carbon nanotube growth process. I'm only knowledgeable to the extent that it was interesting. The work was primarily experimental, so the theory of the ferrofluids was not discussed when I was paying attention.

However, note that iron filings also form clumps with peaks ... so it is probably just the connection of one end to the next, with greater entropy and lower energy from the peaked distribution.

Somebody may have written a paper about this ... try Google Scholar with a few carefully selected search terms!

 

[Andy Resnick]

Ok, so better is not try drop magnet to ferrofluid, yeah? :D

Ferrofluid in magnetic field forms peaks. I read that it is the best variant to the lowest energy of magnetic energy and all system (but not for surface tension). So, it is nice, but I still don't understand to much. So, I think that you know about ferrofluid a lot, so I want to ask you: why the ferrofluid makes peaks? why the particles don't go near to magnet and stay there? it can be better for energy.

It's called the 'normal field instability":

http://pages.csam.montclair.edu/~ye..._Instability/EngelEtAl_1DRosensweigInstab.pdf
http://www.google.com/url?sa=t&rct=...OVCM23dvbeW4IMg&bvm=bv.71126742,d.aWw&cad=rja

http://www.sciencedirect.com/science/article/pii/0304885387900576