A comparative study of magnetic properties of LiFePO4 and LiMnPO4

A detailed comparative study of the magnetic properties of LiFePO4 and LiMnPO4 samples is presented. Magnetic susceptibility, electron paramagnetic resonance and Li-7 NMR experiments were performed on samples as prepared for electrochemical studies. The ground state of LiFePO4 seems to be that of a collinear antiferromagnet and very robust against crystal imperfections. On the other hand, our LiMnPO4 samples possess a weak ferromagnetic ground state with a transition temperature T-N = 42 K. We suggest that solitons may be very important magnetic excitations in these systems and that pinning of solitons below T-N together with frustration plays a decisive role in the formation of the weak ferromagnetic state in LiMnPO4. The differences between the magnetic properties of these two samples reflect also the differences between their electronic structures and may thus be important for the electrochemistry of LiFePO4 and LiMnPO4.