Low energy magnetic excitation in lightly electron doped LaCo1-yNiyO$_{3}$

We investigated the magnetic excitations in lightly doped LaCo$_{1-y}$Ni$_{y}$O$_{3}$ (y=0.005, 0.01) via inelastic neutron scattering measurements (INS). The substitution of Ni$^{3+}$ (3d$^{7})$ for Co$^{3+}$ (3d$^{6})$ nominally introduces an electron in the system. At 4 K, a low energy magnetic excitation is present with a characteristic energy of 1.2 meV. On warming above 30 K, the excitation smears out due to the appearance of the more intense 0.6 meV excitation previously observed in pure LaCoO$_{3}$, the latter associated with single ionic transitions within the excited state manifold. The new excitation is associated with dynamic ferromagnetic correlations as measured from INS measurements on single crystals. The effective magnetic moment is estimated to be about 12 $\mu _{B}$/Ni for the y = 0.005 sample at 10 K. The magnetic field dependence of the 1.2 meV excitation yielded an estimate for the value of g to be about 10 for the y = 0.01 sample. The large magnetic moment and g value at low temperatures may be an indication of the existence of a magnetic ground state of the Co$^{3+}$ ions where the Ni$^{3+}$ and Co$^{3+}$ ions engage in ferromagnetic coupling.