Hello Charanjeet Singh

You try find it in COD (Crystallography Open Database)?

The JCPDS number is 51-1879

But its more easy find the specific peaks (2theta) and associated planes in the papers.

Suggested papers for XRD of hexagonal ferrites:

Structural and magnetic behavior of cobalt doped Ba0.5Sr0.5Fe12O19

nanoparticles synthesized by chemical co-precipitation technique. Applied Mechanics and Materials Vol 274 (2013) pp 406-410

Magnetic properties of Ni–Co doped barium strontium hexaferrite

August 2012Journal of Materials Science: Materials in Electronics 23(8) DOI: 10.1007/s10854-012-0631-y

here Charanjeet Singh

Charanjeet Singh

In case you can't open a .cif here's a .pdf.