Long range antiferromagnetic (AFM) ordering of Ni spins in Ni2NbBO6 has been studied with single crystal from spin susceptibility measurement and comparedwith the ab initio calculation results consistently. Below TN = 23.5 K, the S = 1 spins align al
ong the a direction for edge-shared NiO6 octahedra which form crystallographic armchair chains along the b direction. The isothermal magnetization M(H) below TN shows spin-flop transition for magnetic field above 36 kOe along the a axis,which indicates the spin anisotropy is along the a direction. The electronic and magnetic structures of Ni2NbBO6 have also been explored theoretically using density functional theory with generalized gradient approximation plus on-site Coulomb interaction (U). These calculations support the experimentally observed antiferromagnetism of Ni2NbBO6. In particular, the long range AFM ordering below TN can be dissected into armchair chains which consists of S = 1 dimers of J2 = 2.43 meV with ferromagnetic (FM) intrachain and interchain couplings of size half |J2|.
The structure, electronic, and magnetic properties of the Mo-doped perovskite La0.7Ca0.3Mn1-xMoxO3 (x < 0.1) have been studied. A significant increase in resistivity and lattice parameters were observed with Mo doping. A marginal decrease in the Curi
e temperature Tc and the associated metal-insulator transition Tp were observed. Magnetization data reveal that long-range ferromagnetic ordering persists in all samples studied and the saturation moment decreases linearly as x increases. Enhancement in magnetoresistance at near Tc in the Mo-doped compounds with an optimum doping value x = 0.05 was observed. The overall experimental results can be explained by considering the induced Mn2+ ions with Mo6+ in the Mo-doped systems, with the strong FM coupling between Mn4+/2+- O - Mn3+.
