could someone tell me how can I find and add Polyaniline-BaFe12O19-CoFe2O4 optical constants (n,k) to fdtd solution material explorer?
You can import arbitrary material data in multiple ways:
a) Obtain material data from third party source or measure them if you have the equipment and import them from file: https://kb.lumerical.com/en/index.html?materials_creating_sampled_data_material.html
b) Use analytic function to describe your material properties:
c) Use one of the advanced material models that come with FDTD (requires you to obtain appropriate coefficients):
Unfortunately, all of the methods above will require you to obtain material data first. Considering that the material you are looking for is not as basic and common as lets say gold or silicon, your best bet might be to browse publications using this material or focusing on similar applications. There is a good chance that they include the refractive index as a figure plot or sampled data.
I’ve tried to find out the complex refractive indices of “Polyaniline-BaFe12O19-CoFe2O4” material. But I couldn’t obtain (n, k) for that composite material. Instead, I discovered the individual optical properties of BaFe12O19 and CoFe2O4 in the following images through the reference articles.
I hope this could be helpful for you.
 Bellad, S. S. & Bhosale, C. H. Substrate temperature dependent properties of sprayed CoFe2O4 ferrite thin films. Thin Solid Films 322, 93–97 (1998).
 Mičica, M. et al. Terahertz material characterization for nonreciprocal integrated optics. in (eds. Cheben, P., Čtyroký, J. & Molina-Fernández, I.) 951615 (2015). doi:10.1117/12.2179449