Low temperature heat capacity Study of Fe(PO3)3 and Fe2P2O7

► We report for the first time heat capacity measurements on Fe(PO3)3 and Fe2P2O7 in the temperature range from (2 to 300) K. ► Theoretical fits at low temperatures suggest that Fe2P2O7 has an anisotropic antiferromagnetic contribution. ► The linear term in Fe2P2O7 disappears by 15 K.