Do you know the crystal structure of your ferrite? If yes, you have to use the Bragg's law to calculate d (interplanar spacing) and using the hkl (for your crystal structure) you can find the lattice parameter. 

here are the links:

https://en.wikipedia.org/wiki/Bragg%27s_law

http://nptel.ac.in/courses/113106032/4%20-%20Crystal%20structure.pdf

http://bama.ua.edu/~mweaver/courses/MTE583/MTE%20583_Class_17.pdf

and you can use the calculators in the internet: http://www.calistry.org/solid-state

You need to plot the XRD patter using Origin software, index the peaks using JCPD card. Then calculating lattice parameters either using Brag law or using Rietveld method. One example can be found in the attached paper of my student.

Article Synthesis, characterization, and sintering behavior of Yb3Al...

thanks but how to get FWHM from origin ?

FWHM can be directly measured from a peak in XRD pattern plotted in origin.

Ashok KR Pradhan

In this video tutorial, I have explained in detail how and how to calculate lattice constants for cubic and orthorhombic structures from the XRD data using OriginLab software. In the case you want to further ask about it, please do comment on the specific video, I'll respond to it shortly. I have provided the practice as well as calculations files here. Thanks

https://youtu.be/Hr3S_f4lktw