| Abstract
| - Differences in the Néel temperatures and reorientation of magnetic moments of LiFeIIPO4 and FeIIIPO4 are explained by the strong anisotropy of Fe2+ in LiFePO4, whereas the isotropy of Fe3+ in FePO4 may explain why the structure is noncollinear. The relative stability regions of collinear magnetic structures for different values of the exchange interactions are determined.
- The magnetic structures of LiFePO4 and of its delithiated form FePO4 (triphylite, olivinegroup, space group Pnma) have been solved using neutron diffraction on polycrystallinesamples. Both compounds show antiferromagnetic behavior below 52 K for LiFePO4 (Fe2+)and below 125 K for FePO4 (Fe3+), characterized by the appearance of extra peaks in theneutron diffraction patterns below the Néel temperature. These magnetic reflections areindexed with a propagation vector k = (0,0,0). The magnetic moments of the four iron atomspresent in the unit cell are oriented along [010] for LiFePO4 and mostly along [100] (with asmall component along [010]) for FePO4. The magnetic structures and the differences in theNéel temperatures are discussed in terms of super and super-super exchange intractionsand of anisotropy of Fe2+. A comparison is made with other olivine compounds with similarcation distribution.
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