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Investigation of hyperfine interactions on magnetic intermetallic compounds by perturbed angular gamma-gamma correlation technique


In the present project we intend to use the Perturbed gamma-gamma angular correlation (PAC) technique to investigate hyperfine interactions in intermetallic compounds that show magnetic ordering. The main goal is to systematically investigate the origin of typical phenomena of crystalline solid compounds, mainly the magnetism, as well as phase transitions, structural defects and electronic structure in families of compounds, in which at least one of the constituents is a rare earth element. Measurement of the hyperfine parameters like the magnetic hyperfine field (Bhf) and the electric field gradient (Vzz) along with the asymmetry parameter (eta) will be carried out in the temperature range of 1.5 K to 1300 K. As such measurements are well localized, we may use as many probe nuclei as possible to substitute different atom sites of the investigated compound. Then, we can measure the local behavior of the hyperfine parameters as well as correlate the results with the characteristic macroscopic properties of each compound with the objective to understand the microscopic mechanisms that give origin to such phenomena. Besides the tradional probe nuclei like 111In(111Cd) and 181Hf(181Ta), the 140La(140Ce) probe, which substitute for rare earth sites, will also be used. This particular nucleus is very useful in magnetic measurements because its nuclear quadrupole moment is very small and, consequently it does not feel quadrupolar interactions that can interfere in the measurements of the Bhf in compounds with no cubic symmetry. Besides PAC measurements we intend to use X-ray and neutron diffractometry to characterize the crystalline and magnetic structure of the samples. Other techniques like magnetometria, resistivity and Mössbauer effect can be used, if necessary, to obtain additional data on the samples... (AU)

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