Hydrothermal syntheses and low temperature magnetic behaviors of ACo3(P2O7)2 (A=Ca, Sr, Ba, Pb)

ACo3(P2O7)2 (A=Ca, Sr, Ba, Pb) has been synthesized hydrothermally. Dc and ac magnetic susceptibilities are measured at various conditions. The magnetic interactions in all four compounds are dominantly ferromagnetic. All four compounds has a ferromagnetic-like long-range ordering at 8.0 K for CaCo, 6.4 K for SrCo, 7.6 K for PbCo, 8.0 K for BaCo. The ordering of PbCo at 7.6 K may contain a glassy component. Moreover, there is an additional phase transition for PbCo at 3.6 K. Once enhancing the external field to 3 kOe, the second phase transition is suppressed. Isothermal magnetizations of SrCo, PbCo and BaCo are quite similar, showing a field-induced metamagnetic transition at 2 K. For PbCo, the low-field ground state is weak ferromagnetic, and the critical filed is 10 kOe. Differently, CaCo is a typical soft weak ferromagnet.