I want to make around 40-200 g of metal cylinders that would ideally have a length of around 1-100 μm in size (smaller preferred). The rods will be made of some ferromagnetic material such as Iron or Nickel.

The reason for this is to make a magnetic field display where the tiny metal rods are submersed in a viscous liquid which is trapped between two clear sheets of material (likely glass or acrylic).

Since these are rods and not balls, this should allow them to stick end to end without bunching up so much and better visualise the magnetic field lines.

Although i'd prefer The rods to be smooth, they don't necessarily have to be a cylinder shape, they just have to have a length to width ratio higher than 2:1 (although i'd prefer a bigger aspect ratio than that).

It is preferred, but not necessary that the rods are all the same length with minimal variation in size.

Last preference is for the metal to look shiny rather than black as this helps a lot with visualising the field lines. I'll take what I can get though.

Haven't found anything online like this but I also don't really know what to search for.

I thought of using thin iron/steel wire and cutting it up but this process would most likely be too difficult and tedious to carry out unless I could construct some machine or jig to do it for me. I also have struggled to find any sort of ferromagnetic wire smaller than 0.1mm which would still be too thick for what I want.

I also thought of long metal shavings but they tend to be twisted and irregular (and possibly too flat) to work well for this.

Perhaps I could use some sort of micro 'cheese grater' to grate pieces off of a metal block?

Could these rods be synthesized via electrolysis somehow?

I'm at a loss so any help or pointers on how to go about this would be greatly appreciated!

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    $\begingroup$ You're better off using a commercially available ferrofluid, rather than synthesizing your own. If you want to synthesize your own easily, try experimenting with plain old iron filings and see if the results are satisfactory. $\endgroup$ Commented Oct 5, 2020 at 11:50
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    $\begingroup$ I offer a weird suggestion: find the finest (flexible) iron or steel wire you can get; cut a piece half as long as the distance between the poles of the magnet. Bind a dozen or so pieces of this length of wire together; attach to one pole of the magnet; they should splay out like the mini-particles you are looking for, but without the mess of liquid etc. Attach another bunch to the other pole. $\endgroup$ Commented Oct 6, 2020 at 13:59

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Here is a relevant 2013 paper: Synthesis of pure iron magnetic nanoparticles in large quantity, to quote:

Free nanoparticles of iron (Fe) and their colloids with high saturation magnetization are in demand for medical and microfluidic applications. However, the oxide layer that forms during processing has made such synthesis a formidable challenge. Lowering the synthesis temperature decreases rate of oxidation and hence provides a new way of producing pure metallic nanoparticles prone to oxidation in bulk amount (large quantity). In this paper we have proposed a methodology that is designed with the knowledge of thermodynamic imperatives of oxidation to obtain almost oxygen-free iron nanoparticles, with or without any organic capping by controlled milling at low temperatures in a specially designed high-energy ball mill with the possibility of bulk production. The particles can be ultrasonicated to produce colloids and can be bio-capped to produce transparent solution. The magnetic properties of these nanoparticles confirm their superiority for possible biomedical and other applications.

So, to answer your question, it actually may be feasible based on more recent work. Note: the article appears in the applied physics section of Journal of Physics, reflecting the likely significance of this topic in this area.

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    $\begingroup$ Thanks for the reply! Ultrasonification + ball milling sounds like a really cool concept and I might play around with that idea myself! What exactly is bio-capping the particle? Is it the same as forming a micelle around an iron particle? A transparent liquid that is also magnetic would be really amazing to make and I can see it being used in a lot of different applications! $\endgroup$ Commented Dec 20, 2020 at 10:43

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