Experimental Evidence of Zero Forward Scattering by Magnetic Spheres

Magnetically induced diffraction patterns by micron sized magnetic spheres dispersed in a ferrofluid disappear at a certain critical magnetic field. This critical field is found to depend on the concentration of the ferrofluid and on the volume of the magnetic spheres. We attribute this effect to the zero forward scattering by magnetic spheres as predicted by Kerker, Wang, and Giles [J. Opt. Soc. Am. 73, 765 (1983)]. We suggest that such a dispersion can be used to study the optical analogues of localization of electrons in condensed matter, the Hall effect, and the anisotropic diffusion, etc. The combination of the micron sized magnetic spheres and the ferrofluid will also be useful to design magnetically tunable photonic devices.

Figure 1

A typical microscope picture of $1.0\mu \mathrm{m}$.

Figure 2

Diffraction pattern for the electric vector parallel to the applied magnetic field in the case of $3\mu \mathrm{m}$ magnetic spheres dispersed in a ferrofluid (28% concentration); (a) $H=0\mathrm{G}$, (b) $H=30\mathrm{G}$, (c) $H=60\mathrm{G}$, (d) $H=100\mathrm{G}$, (e) $H=200\mathrm{G}$, (f) $H=500\mathrm{G}$.

Figure 3

Diffraction pattern for the electric vector perpendicular to the applied magnetic field in the case of $3\mu \mathrm{m}$ magnetic spheres dispersed in a ferrofluid (28% concentration); (b) $H=30\mathrm{G}$, (c) $H=60\mathrm{G}$, (d) $H=100\mathrm{G}$, (e) $H=200\mathrm{G}$, (f) $H=500\mathrm{G}$. Zero forward scattering is observed for $H=100\mathrm{G}$ (d).

Figure 4

Diffraction pattern for the electric vector perpendicular to the applied magnetic field in the case of $2–3\mu \mathrm{m}$ silica spheres dispersed in a ferrofluid (28% concentration) (a) $H=0\mathrm{G}$, (b) $H=30\mathrm{G}$, (c) $H=60\mathrm{G}$, (d) $H=100\mathrm{G}$, (e) $H=200\mathrm{G}$, (f) $H=500\mathrm{G}$.

Figure 5

Diffraction pattern for the electric vector perpendicular to the applied magnetic field in the case of $3\mu \mathrm{m}$ magnetic spheres dispersed in kerosene (a) $H=0\mathrm{G}$, (b) $H=30\mathrm{G}$, (c) $H=60\mathrm{G}$, (d) $H=100\mathrm{G}$, (e) $H=200\mathrm{G}$, (f) $H=500\mathrm{G}$.

Figure 6

Dependency of critical magnetic field ($H_c$) for zero forward scattering on concentration and on the size of the scatterers dispersed in a ferrofluid.