You should set ISPIN = 1 when you include SOC. Including SOC means that your spin direction is noncollinear. If you want to plot a spin-polarized band structure, you need to set ISPIN = 2 and turn off SOC.

I agree with prof.Jaing

Thank you so much for your kind reply

Dear Zeyneb Bordjiba

Regardless of the magnetic state of your system, you can (and in some cases you must) include spin-orbit (SOC) coupling. In case the system is magnetic the effect of SOC is that it it couples both spin-up and spin-down spinors with momentum. Accordingly you can now decompose all the the relevant parameters such as band structure and DOS in terms of magnetization components mx, my and mz. In other words your magnetic structure is now non-collinear (with is a more general term as compared to the collinear terms: spin-up and spin-down). If you use VASP with SOC being turned on, you can get all the information you need to plot spin-projected band structure and DOS in files PROCAR and DOSCAR. Please refer to the manual for more information:

https://www.vasp.at/wiki/wiki/index.php/PROCAR

https://www.vasp.at/wiki/index.php/DOSCAR

Dear Mohammad Saeed Bahramy

Thank you so much for the detailed explanation I have benefited a lot.

Best,

Zeyneb.