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05-15-2018, 05:48 PM
 bistander Gold Member Join Date: Apr 2015 Posts: 1,669
Ferrofluid

Quote:
 Originally Posted by dyetalon I think we should discuss the difference between ferromagnetism and ferrimagnetism. Maybe this will help understand whats going on in the cell. Here's the ordering in different materials and a link: https://en.wikipedia.org/wiki/Magnetic_structure ... What happens if you add these two together?

Hi dyetalon,

Glad to have you join the conversation.

Quote:
 Finally, ferrimagnetism as prototypically displayed by magnetite is in some sense an intermediate case: here the magnetization is globally uncompensated as in ferromagnetism, but the local magnetization points in different directions.

From what I've learned, for the purpose of ferrofluid, the ferrimagnetic and ferromagnetic materials behave very similarly when we're not concerned with Curie temperature, saturation magnetization, and permeability. I don't know about the optical properties.

Here's an interesting look at ferrofluid (I think).

From:
https://www.mnn.com/green-tech/resea...trate-magnetic

I liked this video from that site.

Quote:
 Originally Posted by dyetalon This is what I refer to when I speak of phase cancellation (N minus S) occurring in the cell. If we graph a magnetic field, we obtain a peak at positive maximum (North) and a peak at negative maximum (South). It actually resembles a sine-wave (as seen on an oscilloscope). If we break this down into math, we get +180 degrees and -180 degrees. What happens if you add these two together?
Those little arrows in the diagrams (which I posted from your post) represent magnetic moments of the particles, grains, or domains in the material. The gross magnetic field of a significant quantity of the material is the integral of all those moments. As shown in the diagram, ferrimagnetic material has a "favored" direction of magnetic moments aligned by the external magnetic field therefore, as you put it, the N & S phases, will not totally cancel.

So what happens when you "add these two together", you get what looks very much like ferromagnetism. So much so, ferrimagnetism is covered, and iron oxide on the chart, at the wiki article, which is a pretty good explanation.
https://en.m.wikipedia.org/wiki/Ferromagnetism

Regards,

bi
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