Metamagnetic transitions in the honeycomb lattice Er2Si2O7

We seek to further investigate the metamagnetic transitions in the honeycomb lattice Er2Si2O7. The 1/3-plateau seen in the H||a magnetisation process is rather unusual for a four-sublattice structure. The plateau stabilisation is accompanied by a significant increase of the magnetic unit cell. Non-integer magnetic peaks indexed (0,k+1/2,l+1/2), (0,k+1/4,l+1/4) (0,k+1/3,l) and (0,k+2/3,l), where k and l are integers, appear in a narrow range of an applied field associated with the magnetisation plateau, while the field regions above and below the plateau contain only (0kl) peaks. Some of the non-integer field-induced peaks are not resolution limited, suggesting shorter-range magnetic correlations on the plateau. However, while we have solved the magnetic structure in the H||a,unusual behaviour is seen in applied field H||c in which a magnetic transition at 3.3 kOe is accompanied by a sudden jump of magnetisation. A magnetisation of 2μB per Er3+ is reached after the transition diverging from the predicted Ising-like behaviour. Above this transition, the magnetisation steadily increases and it seems saturation is not reached even at a significantly higher applied field of 70kOe. Observation of the diffuse scattering of the single crystal with the applied field oriented parallel to the c direction of the crystal will verify the true nature of the magnetic structure and also shed light on the cause of unexpected high field behaviour of the magnetisation process along the c-axis.