I was surprised to learn just now that laser toner can be magnetic. However, I suspect that there are non-magnetic or weakly magnetic toners. Did you try to put the dry toner powder into a magnetic field? If so, did it behave like iron filings?

Thank you Dr.Emmanouil Markoulakis, Prof.Joerg Fricke. Dear Prof.Joerg Fricke, I can see that toner powder is magnetic. They are strongly attracted to magnets as shown in figure.

Dear Nguyễn Thanh Lâm

Thank you for opening such an interesting discussion here.

The first attempt to establish and insight into the problem could be date back to NASA's experiments about "Magnetic Fluids" in 60s, and the phrase invented then. One of the main problems was the grinding technique to produce micro- or nano-sized powered of a ferromagnetic material.

As far as i know there are two distinct types of Magnetic Fluids: The Metallic Fluids and Ferro-Fluids.

The first category covers all liquid shape of metallic materials in any desired temperatures. Obviously it includes molten metals and metals such as Mercury. The members of this category show normal metallic behavior when facing a normal magnetic or electromagnetic field. But at higher magnetic intensity, their fluidity made then to interact physically by the introduced filed by shape deformation. you can not detect these interaction using conventional magnets, even using Neodymium one.

The other category, consists of a fluid of specific viscosity and micro- to nano- sized grind Ferromagnetic powder. Such an very small size for power particles is a requirement to ensure the uniformity of the resulted mixture and to reduce the multiple-crystal of Ferromagnetic matter. When the mixture exposed to a magnetic field, the nano-sized particle start to rotate to be oriented in parallel with magnetic Field lines. As these particles are ferromagnetic and are essentially tiny magnets, the final magnetic filed will be strengthen significantly. In resulted configuration, more aligned ferromagnetic particles, more string magnetic field.

but the are some contradicting parameters:

1) there are limited number of particles

2) the particles are not really single-crystal

3) the viscosity of carrying fluid is not zero

4) now configuration of particles in mixture results now physical formation of it

5) stronger internal magnetic Field required the particle to follow it.

To recapitulate, the surface will be deformed as long as the tendency of particle to be aligned become equal to internal viscosity of mixture.

i try to explain the nature as simple as i can and as far as i know about.There are numerous papers which you can obtain by Googling.

Thank you for your time

Dear Dr.Ahmad Esmaeilkhah.

Thank you for your very useful information.Technically, I realize that the problem here is that I have not yet found laser toner containing nanosized magnetic iron particles. I use some laser toner from Korea, Taiwan and Vietnam but they are not working.

Dear Nguyễn Thanh Lâm

please find and read the article:

Effect of Micro- and Nanomagnetite on Printing Toner Properties

by: Maryam Ataeefard, Ebrahim Ghasemi, and Mona Ebadi

Link: Article Effect of Micro- and Nanomagnetite on Printing Toner Properties

Here is the abstract:

Toner is a main component of electrophotographic printing and copying processes. One of the most important ingredients of toner is magnetite (Fe3O4) which provides the tribocharging property for toner particles. In this study, nano- and microparticles of Fe3O4 were synthesized using the coprecipitation method and different amounts of lauric acid as a surfactant. The synthesized nano and micro Fe3O4 was then used as the charge control agent to produce toner by emulsion aggregation. The Fe3O4 and toner were characterized by X-ray powder diffraction (XRD), atomic gradient force magnetometry (AGFM), dynamic laser scattering (DLS), particle size analysis, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The results show that the optimum amount of surfactant not only reduced particle size but also reduced the magnetite properties of Fe3O4. It was found that the magnetite behavior of the toner is not similar to the Fe3O4used to produce it. Although small-sized Fe3O4 created toner with a smaller size, toners made with micro Fe3O4 showed better magnetite properties than toner made with nano Fe3O4.

To display the magnetic field lines, the indicator particles have to fulfill 2 preconditions:

Thus any attempt to use nano- or micro-scale particles is not really applicable, the more when they are able to easily move towards one of the poles. Iron filings with limited capability to move are a reasonable indicator :)

P.S.: the usual way to feed the toner is a magnetized spindle; thus I expect all usual toners to be somewhat magnetic.

Thank you very much, Dr.Ahmad Esmaeilkhah and Dr.U. Dreher. I totally agree with you. However, I think that the problem may come from magnets. The magnets must be very strong to show the magnetic lines.

http://www2.mie.utoronto.ca/labs/MUSSL/Ferrofluids.htm

However, the experiments do not explicitly mention the parameters of the magnet.

I also found on Amazon that a magnetic liquid sold could be stimulated with a small magnet, perhaps because these magnetic liquid was synthesized from specific components and special methods.

https://www.amazon.com/dp/B01E60CLUG/ref=sspa_dk_detail_9?psc=1&pd_rd_i=B01E60CLUG

Thank you for your help, Dr.Emmanouil Markoulakis, Prof.Joerg Fricke, Dr.Ahmad Esmaeilkhah, Dr.U. Dreher. We see that the best recipe for ferrofluid is laser toner (contain iron nanoparticles) and motor oil. Spikes starts to appear in surface of ferrofluid but unclearly because of weak magnet.

https://drive.google.com/file/d/0B0yL-xLCx0YfU21xeFNfT2hnZzNRQzhWSGJDYjh3dFUtOGMw/view?usp=sharing

Dear Dr. Nguyễn Thanh Lâm

there is an important question. What is the man reason of doing such an experiment?

As you may know, the ferro-fluid was first stirred some investigation to control and maintain the fuel pressure in rocket porpulsion systems by NASA.

Also there are commercial materials which are ready to use. On the other hand there are better way to show and visually demonestrate the magnetic field in 2D and 3D coordination system.

Can you please clarify more about the reasons your are conduction such experiments. By this way, we may help or contribute better

thank you in advance.

Dear Dr.Ahmad Esmaeilkhah,

We need to prepare some impressive experiments to show our students.

Thank you very much.

If you have access to obsolete magnetic storage mediums (data, video or audio tapes/disks), you could try soaking the medium in acetone to free the ferromagnetic particles. A magnet could be used to isolate the the particles.

Thank you very much for your help, Dr. Søren Kyale