With powder neutron diffraction you do not have the directional information of the scattering vector Q. You just get the magnitude of Q only. So to make (Q-x,Q_y) you need single crystal neutron/X-ray data.

It's very simple, no need for book here Q = 2*pi/d = 4*pi*sin(theta)/lambda, get any worksheet progam that can do that conversion on your 2theta column and you'll get your graph in Q units. Many Rietveld programs do it for you automatically (e. g. GSAS in liveplot window Options/X-units/Q).

The only posible controversial issue with converting CuKalpha data into Q or d units is that you have peaks originated in 2 different wavelengths in your pattern (Kalpha1=1.5406 Å an Kalpha2=1.5440 Å, unless you use a monochromator that strips Kalpha2) so when you convert to Q using just lambda average (1.5418 Å) neither your Kalpha1 nor your Kalpha2 peaks will be located in the correct Q values. It may be a good idea if you have a nice splitting (e.g very narrow peaks) to use Kalpha1 for the conversion and then ignore the Kalpha2 peak (since that will be off place). But for peaks at low angles this option will have them slightly off and using Kalpha average is better. In any case and just for comparison purposes you should be very clear in the selection of lambda for your equation and consider it when doing the comparison with other (neutron or X-ray) data.

Eventually it would be advisable to do a mathematical substraction of Kalpha2 component, but as said, just for display/comparision purposes, NEVER EVER use such data for a refinement!!!!

Best of luck!

Thank you very much. Its really clear and easy. I use GSAS for powder XRD and till now I never did NPD for magnetic structures. Sometimes for thin films (or single crystals) I see the map (Q_x,Q_y) to explain their magnetic structures or propagation vector which decides whether structure is G, A, C or some helical structure. (please correct me If I am wrong in framing the question). Can you please tell how this type of mapping done.

With powder neutron diffraction you do not have the directional information of the scattering vector Q. You just get the magnitude of Q only. So to make (Q-x,Q_y) you need single crystal neutron/X-ray data.

Thank you so much all of you. @Tapan Chatterji, Can you please tell how to get information from these type of maps and what type? Please suggest some reference/ book regarding these details.

If you have a single crystal then you can do a neutron diffraction experiment. First you have to orient the crystal. If say the [001] axis is vertical then you will have (hk0) scattering plane. You can go to a nuclear or structural reflection and then scan along h or k or the diagonal direction if you wish. The orientation matrix will enable you to scan along any reciprocal direction. You measure intensities for different reciprocal points. Now with e.g. MATLAB software you can make a color plot of the reciprocal plane you have scanned. If you are lucky you may see extra reflections not allowed by the structure. These are may be magnetic reflections. But you have to prove it by checking its temperature dependence. These reflections should disappear above T_N for an antiferromagnetic structure. You can determine the propagation vector k of the magnetic structure say k = (1/2,1/2,0) for example. This means that your magnetic unit cell is double the structural unit cell along both a and b axes. Now if you measure intensities of several magnetic and structural reflections and make a model of the magnetic structure then you can check whether the model is correct or not by calculating the intensities from model structure.

I do not wish to write book about the determination of magnetic structure in Research Gate. But you can consult: Magnetic neutron scattering, ed. T. Chatterji, Elsevier 2006.

There is another way of mapping the reciprocal plane. For that you have to have a multidetector covering a large 2theta range. You have orient the crystal with a crystallographic axis say [1,-1,0] vertical. In that case your scattering plane is (hhl) . Now you make a sample rotation (omega) scan. If yoyu turn omega by 360 deg then you will have a complete map of omega-2theta. Now by a standard software you can transform this map into the reciprocal map of (hhl). This reciprocal map will contain both structural and magnetic reflections if the radiation used is neutron. With x-ray it is difficult but not impossible to measure magnetic reflections (you have to use synchrotron X-ray) but you can easily get structural reflections. You can have a mapping of three dimensional reciprocal space if your detector is two-dimensional with a good coverage. If you look at the chapter 7 of the above mentioned book (p. 357 and 359) you will see some color plots of (hhl) plane. This method is very useful for studying structural and/or magnetic diffuse scattering.

Thank you so much for detail explanation. I got this book which is very nice but a bit difficult for me. I am interested to understand the difference in magnetic structure of isostructural compounds YCrO3 and HoCrO3 using NPD (though presently I dont have NPD data).We attempt a basic comparative study of these compounds (http://iopscience.iop.org/0953-8984/25/21/216004/) by XRD and dc magnetization measurements which indicates weak ferromagnetic nature. I ll try to get some understanding regarding antiferromagnetic structure determination by this book. Thank you again and I may ask more clarification in future.

Brajesh you will not go far ahead with just powder RCrO3. A lot of work has already been done on powder samples. If you have single crystal then make real break through. You should try to grow single crystals!

Thank you. I am submitting thesis this month. Single crystal not possible here but oriented thin films I can try on different substrates. I dont know how far these analysis can be done for thin films.