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 LixNi2-xO2, 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 T-N=327 K to robust uncompensated magnetic order at T-N=240 K when x is close to 0.7, and to glassy A-type antiferromagnetism of x=1.00 at T-N=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).