Why neutron diffraction is better than x-ray diffraction for studying magnetic material?
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X-ray and neutron diffraction are complimentary probes and should be used judiciously. One must know the basic principles of these two techniques. The main characteristic of X-ray diffraction is that since X-rays are scattered from electrons, the scattering power (form factor) is proportional to the number of electrons in the atom, it increases linearly as a function of Z, the atomic number. The neutrons are scattered from the nuclei of the atoms and their scattering power is not a smooth function of Z, there are many sudden variations specially for different isotopes of the same atoms. If you have H atoms in presence of heavy atoms like rare earth or actinides then the scattering from the H atoms is completely masked by the huge scattering from the heavy atoms in case of X-ray scattering whereas for neutron diffraction this is not so. Again scattering power of H and deuterium is not only different in magnitude but also different is sign. So if you have H atoms in your structure that participate in the order-disorder transition then you will see the transition much better in neutron diffraction. This is also so for O atoms. Also order-disorder transition is associated with dynamics and this can be much better studied by inelastic neutron scattering because the energy of thermal neutrons is of the same order of magnitude of the atomic dynamics. But again you should not underestimate the power of X-ray diffraction technique. Historically much of the physics of order-disorder transition has been successfully studied by X-ray diffraction in favorable cases.
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X-ray and neutron diffraction are complimentary probes and should be used judiciously. One must know the basic principles of these two techniques. The main characteristic of X-ray diffraction is that since X-rays are scattered from electrons, the scattering power (form factor) is proportional to the number of electrons in the atom, it increases linearly as a function of Z, the atomic number. The neutrons are scattered from the nuclei of the atoms and their scattering power is not a smooth function of Z, there are many sudden variations specially for different isotopes of the same atoms. If you have H atoms in presence of heavy atoms like rare earth or actinides then the scattering from the H atoms is completely masked by the huge scattering from the heavy atoms in case of X-ray scattering whereas for neutron diffraction this is not so. Again scattering power of H and deuterium is not only different in magnitude but also different is sign. So if you have H atoms in your structure that participate in the order-disorder transition then you will see the transition much better in neutron diffraction. This is also so for O atoms. Also order-disorder transition is associated with dynamics and this can be much better studied by inelastic neutron scattering because the energy of thermal neutrons is of the same order of magnitude of the atomic dynamics. But again you should not underestimate the power of X-ray diffraction technique. Historically much of the physics of order-disorder transition has been successfully studied by X-ray diffraction in favorable cases.
Hope it helps.
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