Magnetic behaviour of NpAs2 from Mössbauer spectroscopy |
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Authors: | M Bogé J Chappert L Asch GM Kalvius A Blaise JM Fournier D Damien A Wojakowski |
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Institution: | Centre d''Etudes Nucléaires de Grenoble, Departement de Recherche Fondamentale, 85X, F-38041 Grenoble Cedex, France |
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Abstract: | The Mössbauer hyperfine spectra of the 60 keV resonance of 237Np in powder and single crystal absorbers of NpAs2 were measured between 4.2 and 60 K. Below 18 K a simple magnetic plus quadrupole pattern is seen in accordance with a ferromagnetic spin structure in tetragonal NpAs2. The isomer shift favors the 4+ charge state, the hyperfine field of 288 T implies a moment of 1.5μB at the Np ion. The large reduction compared to the free ion values points towards a strong mixing of the electronic ground state by crystalline field interactions. Above 18 K the spectrum changes into a complex hyperfine pattern indicating a sinusoidally modulated spin structure. Near 54 K a transition into the paramagnetic state is observed. Both magnetic transitions (18 and 54 K) exhibit a feature typical for a first-order character. |
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