I want to improve the remanence of magnetic nanoparticles. What are the parameters that influence remanence?
Read p. 300-301 of the book "Magnetism and magnetic materials", J.M.D. Coey, Cambridge 2009. You may get some idea there.
Before trying to give an answer, I will ask some questions first, as your question is somewhat vague. How large are the particles. What is the material and what is its magnetic anisotropy. Are the particles in solution or are they deposited onto a surface (maybe even in a solid matrix). Do you need bio-compatibility? If we know that, your chances in getting a proper answer definitively increase.
^The agglomerates of the Iron nanoparticles are around 100 micron in size. The individual particles are of ~40 nm in order. I don't have any information regarding anisotropy. The particles are in powder form. Bio-compatibility, if achieved is appreciated but not necessary as such. My question is a broad one to understand the parameters influencing the phenomenon.
Remanence is, in general a tricky thing, and as you might guess depends on several parameters. The most important one is probably the magnetic anisotropy, as it has influence on domains, domain walls, and thermal fluctuations (from your question I assume that the particles are not superparamagnetic). Your particles are small and are likely in a monodomain state, but maybe not entirely homogeneous. If you have BCC iron you have a cubic anisotropy and within your cluster a certain distribution of axes directions. This will be affected by Brownian motion of the particles, so low chances of increasing remanence by aligning the axes. Second point here are probably thermal fluctuations. Bulk BCC iron has an anisotropy constant of some 10^4 J/m^3, but that can be smaller or larger in your case. In general, you would try to increase anisotropy to decrease fluctuations and inhomogeneities. Hence, a proper surface decoration is required, maybe with an antiferromagnetic material? With respect to intra-cluster dipolar interactions: those are probably very small. Furthermore, they can stabilize or destabilize the order, depending on local geometrical arrangement. Nevertheless, large clusters will eventually be inhomogeneous and present some sort of flux closer mechanism, therefore, decreasing the remanence. On the other hand, decreasing the cluster size increases the motion/ rotational fluctuations of single particles. So, as mentioned before: it is a tricky thing.
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