Study of nuclear (chemical) and magnetic structures using neutron scattering

Full text: Neutron is a nuclear particle with zero charge. Thermal neutrons have de Broglie wavelength of ∼ 1 A. These properties make the thermal neutrons suitable for probing the positional arrangements of atoms, ions or molecules in condensed matter. Neutron also processes a magnetic moment of -1.913 nuclear magnetrons, which makes the thermal neutrons an ideal probe to study the magnetic structure of materials. Neutron being a charge less particle it can penetrate high into matter and therefore, allows one to study bulk materials. Unlike x-ray scattering, neutron nuclear scattering cross section is governed by a short-range nuclear interaction and it does not vary monotonically. This allows one to locate lighter atoms in presence of heavier atoms. Nuclear scattering even allows one to detect various isotopes of an atom. Unlike x-ray magnetic scattering, the neutron magnetic scattering length is comparable to nuclear scattering length (∼10-12 cm) and it makes neutron magnetic scattering a very powerful tool for magnetic studies. Neutron scattering research has spread in physics, chemistry, metallurgy, biology and other fields. In my talk, the principle and application of thermal neutrons to study nuclear (chemical) and magnetic structures will be discussed. The talk will also cover the use of polarized neutron for magnetic studies in mesoscopic length scale. Recent results, on perovskites of Mn and Co showing CMR behaviour and Cr based perovskites showing rich structural and magnetic phase diagrams, hexacyanometallate-type molecular magnetic materials showing an ordering of high spin and low spin Fe ions, hydrogen storage materials with non-collinear magnetic ordering, uranium based intermetallic compounds showing exotic physical properties, obtained using neutron facilities at Dhruva reactor will be presented. (author)