Saturation magnetization of magnetic powder form has unit in emu or emu/g , but in case of magnetic fluid [ ferro fluid ] the units are represented in Gauss or Tesla , what is the difference between the saturation magnetization in powder and fluid form ? Also ,10 nm nominal diameter particles exhibits saturation magnetization of 70 emu/g in the form of powder , but has 200-300 Gauss [ 20-30 mT] in the form of fluid, how and why these powder and fluid form were differentiated corresponding to their units.
The units do not depend on the shape of the particles and the state of aggregation. They can be converted into each other rigidly by certain rules.
Dear Sergey ,
Thanks for your answer , I was aware of this conversion , what is not clear for me is a company named ferrotec has displayed the information of their product [ magnetic nanoparticles - powder and fluid form ] , powder form is given in emu/g and fluid form is given in Gauss/Tesla , can you please explain why they have used two different form of unit [ please check the attachment ].
Dear Vikram,
A ferrofluid or a magnetic fluid is a stable colloidal dispersion of a large number of nano-sized magnetic particles. These particles are usually stabilized by a surfactant and the fluid behave as superparamagnetic material. Its magnetization is given by
M = nm L( mu x H/kT) where L is the Langevin function and m domain magnetization of the particles used to prepare the fluid such as magnetite etc. and n is the number concentration. The magnetite as you have mentioned has saturation magnetization ( you know that the nanomagnetic particles are single domain particles) 70 emu/gm . Using above formula the saturation magnetization (H tends to infiity) of the fluid will be in Gauss. Its actual value will be depend on n.
I hope the matter is clarified.
Dear Dr.Mehta,
Nice to get a reply from you after long time , i was aware that the single domain particle exhibit much higher magnetization in the range of 70-80 emu/g , you can check the attached file in my previous answer , the matter which i was not clarified is , the company has mentioned the magnetization units for powder in emu/g and in fluid form it was mentioned in Gauss , as per my understanding the magnetization is obtained as en effect form the applied magnetic field B [ Gauss ] , in such case why the unit of applied magnetic field is used to describe the saturation magnetization of the material , we can say that at a particular field this material is getting saturated and hat saturation can be given in emu/g . i can understand the conversion between emu/g > A/m which in turn can give the values in Oe [ https://www.researchgate.net/post/How_can_I_convert_emu_gm_into_A_m ] . But the point is for the same 10 nm sized particle why the units is represented as emu/g for powder and Gauss for fluid , is there any specific reason that nanoparticle dispersion in fluid form should be represented in Gauss [ applied magnetic field ] rather than emu/g , need your valuable comments , kindly help .
With due respects I do not want to second guess the reason for the two different values,perhaps they have a better handle on the mass of the magnetic powder while being less sure of the precise mass of magnetic component in the ferrofluid.Anyway, emu/g can be multiplied by the density to get the SI unit for M,ie, A/m Also T is not appropriate for M, it should be divided by the permeability of free space and will again yield M in A/m for a direct comparison but I am sure yo already know all this
Dear Vikram,
Yes, I see yourpoint. In fluid as you know each particle is coated. So its net magnetization will be less than single particle. Probably this may be the reason. You may get further explanation from Dr. Kuldeep Raj of Ferrotec.
Special thanks to Dr.Mehta for providing valuable information and Prof. S.M.Bhagat for the clarification.
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