Synthesis, Crystal Structure, and Cooperative 3-5 Magnetism in Rock Salt Type LiNiOsO and LiNiOsO.

Two new transition metal oxides with the nominal chemical compositions of LiNiOsO and LiNiOsO were successfully synthesized. Both compounds crystallize in an ordered rock salt structure type in the monoclinic 2/ space group. The crystal structures were determined using both synchrotron X-ray and time-of-flight neutron, powder diffraction data. In both phases, Ni ions are present while oxidation states of osmium are +6 and +5 in LiNiOsO and LiNiOsO, respectively. Ni ions in the hypothetical fully ordered phase form a honeycomb arrangement in the crystallographic plane and these hexagons are centered by osmium ions. The magnetic layers are separated along the axis by the octahedra, which are centered by Li (or Li/Ni, depending on the chemical compositions). Crystal structure refinements reveal that there is some degree of mixed occupancy in cationic positions. Temperature dependent magnetic susceptibility data for both phases show ferrimagnetic transitions with predominant antiferromagnetic (AFM) interactions among 3d electrons of nickel and 5d electrons of osmium. Iso-thermal magnetization loops as a function of the applied magnetic field below the transition temperatures confirm the ferrimagnetic nature in magnetic transitions. Temperature dependent heat capacity data, however, did not exhibit any anomaly in either phase, indicating the absence of long-range magnetic ordering. The lack of long-range order for both Os and Os-based compounds was also confirmed by low temperature neutron diffraction data down to 10 K. Temperature dependent AC magnetic susceptibility data in various frequencies for both samples indicate that LiNiOsO exhibits spin-glass-like behavior, while the transition temperature for LiNiOsO is nearly frequency independent.