Neutron-diffraction, magnetic-susceptibility, specific-heat, and Mössbauer-effect studies of NaFeP2O7 reveal that it is a normal Heisenberg isotropic three-dimensional antiferromagnetic material with a Néel temperature of 29.0 K. NaFeP2O7 has the monoclinic P21/c magnetic space group, which is the same as the nuclear crystallographic space group. The easy axis of magnetization lies in the monoclinic ac plane at an angle of 21.0° from the c axis. The specific-heat measurements reveal a λ-type anomaly at 28.7(2) K. A molecular-field model analysis indicates that the intrasublattice magnetic exchange coupling Jaa=Jbb=-0.37 cm-1, whereas the intersublattice coupling Jab=-0.61 cm-1. No evidence for L-type ferrimagnetism is observed.
R. C. Mercader et al., "Mössbauer-Effect, Magnetic, and Neutron-Diffraction Study of NaFeP₂O₇," Physical Review B, vol. 42, no. 1, pp. 25-32, American Physical Society (APS), Jul 1990.
The definitive version is available at http://dx.doi.org/10.1103/PhysRevB.42.25
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