Observation of field-induced anomaly in high-field magnetization on a complex spin-driven multiferroic compound, LiCu_2-z Zn _z O₂

We performed high-field magnetization measurements in the pulse magnetic fields up to 55 T at low temperatures on a doped LiCu_2-z Zn _z O₂ (z=0.07). When H // c-axis, one anomaly was clearly observed in dm/dH curves at ∼9 T. The anomaly broadens as temperature increases and disappears at ∼15 K, which is close to the critical temperature of spiral spin phase and the formation of isolated spin-dimer. Interestingly, an additional peak shows up at 4.2 K, indicating a possible boundary at ∼5 K. On the other hand, when H // a-axis, one broad anomaly can be distinguish which is centered around 11.8 T. However, this anomaly only appears at T≤5.5 K, which is much lower than 15 K, indicating the origin of this anomaly could be different with those in H // c-axis. It is probably comes from the broken one-dimensional chain and the complex inter-chain interactions.