Magnetic ordering of monoclinic FeNaP₂O₇ studied by Mössbauer spectroscopy

Abstract

Mössbauer spectroscopy in zero applied field performed on powder samples of monoclinic FeNaP₂O₇ denote spontaneous magnetic ordering at temperatures below 29.2±0.2 K. Preliminar results from susceptibility and neutron diffraction measurements, currently in progress, establish the same P2₁/c space group as the crystalline structure and an equally sized magnetic cell for the array of spins. The hyperfine fields of the two antiferromagnetic sublattices obtained from Mössbauer spectra display coincident Brillouin-type temperature dependences with an extrapolated OK value of 55.0±0.3 T. Below the Néel temperature the spin orientation does not change relative to the crystalline axes. Mean field theory self-consistent calculations performed in order to estimate the relative magnitudes of the exchange interactions produced the values:J _AB=−0.61 cm⁻¹, andJ _AA=−0.37 cm⁻¹. The antiferromagnetism of the system is likely to originate in the different relative numbers of superexchange pathways between sublattices.