On the 240 K anomaly in the magnetic properties of LiNiO2

In this work, results of X-band ESR spectroscopy, ac-magnetic susceptibilit y and X-ray powder diffraction measurements on Li1-xNi1+xOx (x = 0.02 and x = 0.07) are presented and discussed. While the susceptibility of the compo und with x = 0.02 is shown to follow a Curie-Weiss law, with a Weiss temper ature of the order of 30 K, the compound with x = 0.07 is found to order fe rromagnetically below similar to 80 K. However, an additional anomaly is ob served in the magnetic properties of this latter compound at around 240 K. We attribute this anomaly to the presence of macroscopic Ni-rich regions wh ich order ferrimagnetically below this temperature. This phenomenon is diff erent from the bulk ferromagnetism that occurs at much lower temperatures, and allows us to discard earlier suggestions proposed in the literature in which the 240 K anomaly has been considered as denoting an intrinsic phenom enon.