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Title: Mössbauer spectroscopy, magnetization, magnetic susceptibility, and low temperature heat capacity of α-Na2NpO4
Authors: Smith, A.L
Hen, A
Magnani, N
Sanchez, J.-P
Colineau, E
Griveau, J.-C
Raison, P.E
Caciuffo, R
Konings, R.J.M
Cheetham, A.K 
Keywords: Antiferromagnetism
Ground state
Magnetic susceptibility
Antiferromagnetic orderings
Heat capacity measurements
Low temperature heat capacities
Physical and chemical properties
Quadrupolar transitions
Quadrupole coupling constants
Ssbauer spectroscopies
Structural environment
Specific heat
Issue Date: 2016
Publisher: Institute of Physics Publishing
Citation: Smith, A.L, Hen, A, Magnani, N, Sanchez, J.-P, Colineau, E, Griveau, J.-C, Raison, P.E, Caciuffo, R, Konings, R.J.M, Cheetham, A.K (2016). Mössbauer spectroscopy, magnetization, magnetic susceptibility, and low temperature heat capacity of α-Na2NpO4. Journal of Physics Condensed Matter 28 (8) : 86002. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
Abstract: The physical and chemical properties at low temperatures of hexavalent disodium neptunate α-Na2NpO4 are investigated for the first time in this work using Mössbauer spectroscopy, magnetization, magnetic susceptibility, and heat capacity measurements. The Np(VI) valence state is confirmed by the isomer shift value of the Mössbauer spectra, and the local structural environment around the neptunium cation is related to the fitted quadrupole coupling constant and asymmetry parameters. Moreover, magnetic hyperfine splitting is reported below 12.5 K, which could indicate magnetic ordering at this temperature. This interpretation is further substantiated by the existence of a λ-peak at 12.5 K in the heat capacity curve, which is shifted to lower temperatures with the application of a magnetic field, suggesting antiferromagnetic ordering. However, the absence of any anomaly in the magnetization and magnetic susceptibility data shows that the observed transition is more intricate. In addition, the heat capacity measurements suggest the existence of a Schottky-type anomaly above 15 K associated with a low-lying electronic doublet found about 60 cm-1 above the ground state doublet. The possibility of a quadrupolar transition associated with a ground state pseudoquartet is thereafter discussed. The present results finally bring new insights into the complex magnetic and electronic peculiarities of α-Na2NpO4. © 2016 IOP Publishing Ltd.
Source Title: Journal of Physics Condensed Matter
ISSN: 0953-8984
DOI: 10.1088/0953-8984/28/8/086002
Rights: Attribution 4.0 International
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