Mössbauer spectroscopy at high pressure on magnetic neptunium compounds

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Abstract
The Mössbauer transition in127Np was used to study the volume dependence of magnetic parameters like the hyperfine field B and the ordering temperature Tc or TN in intermetallic compounds of Np. Typical examples are NpOs2, NpAl2, NpCo2Si2, NpAs and NpSn3-. The spectrometer employed a clamp device with a high pressure cell based on opposite boron-carbide anvils and allowed measurements up to 100 kbar at temperatures between 300 K and 2 K. The data were mainly used to gain information on the degree of delocalization of 5f-electrons, that is, whether the compound resembles in its magnetic properties more a typical rare earth (4f) or a 3d transition material. Most of the high pressure results can basically be understood in terms of accepted models of 5f-electron structure. A most surprising behavior, however, was seen for NpSn3-. Although this compound is considered on account of its bulk magnetic properties a prototype itinerant electron antiferromagnet, the pressure dependencies of Bhf and TNreveal rather localized f-electron behavior. For NpAl2 the electronic fluctuations connected with the delocalization process were studied and found analogous to those seen in rare earth compounds of intermediate valence. In NpAs a new high pressure magnetic phase could be detected.