Chemical inhomogeneity, short-range order, and magnetism in the LiNiO2 -NiO solid solution.

NiO:Li is an early exemplar for which hole-doping of a correlated insulator gives rise to rich and varied magnetic behavior. It is also an important system from the viewpoint of p-type transparent conducting oxides, and is representative of a large class of materials that have been used in lithium ion batteries, since the end-member compound, LiNiO2 , belongs to the class of layered cathode materials. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. Here a comprehensive investigation of the solid solution Lix Ni2-x O2 , examining samples of precise stoichiometry using a combination of high-resolution synchrotron X-ray powder diffraction and SQUID magnetometry, is provided. The focus is on the interesting region between 0.40<x<1.00 in which the magnetic ordering temperature changes drastically with composition. The magnetism evolves from strong G-type antiferromagnetism of x=0.40 with TN =327 K to robust uncompensated magnetic order at TN =240 K when x is close to 0.7, and to glassy A-type antiferromagnetism of x=1.00 at TN =9 K. This study demonstrates this magnetic behavior is linked to the Li-Ni chemical order that develops from short- to long-range. The interfaces between ordered domains give rise to magnetic exchange bias, which manifests as a shift in the magnetization-field loop for samples with nanoscale coherence lengths (0.54<x<0.66).