Abstract:
La0.5Sr0.5CoO3−δ system displaying coexistence of metallicity and ferromagnetism, and the interplay between distinct spin states of Co ions has gained significant attention from the fundamental as well as the
applications point of view. In this regard, the effect of V
5+ doping on the dynamics of spin and oxidation
states of Co ions in the La0.5Sr0.5CoO3−δ system has been studied using structural, X-ray photoemission
spectroscopy, magnetic and transport measurements. The La0.5Sr0.5Co1−xVxO3−δ (x = 0, 0.01, 0.02 and
0.1) series was prepared by conventional solid-state reaction method and its chemical homogeneity was
established by inductively coupled plasma mass spectroscopy. The increase of lattice parameters/volum e
with increasing V
5+ content in rhombohedrally crystallized (R c) samples is attributed to the presence of
Co2+ ions (with higher ionic radii). The presence of Co2+ ions and the reduction of Co3+ ion concentration
with V substitution is verified from the results of core-level photoemission spectra of Co. Detailed magnetic
measurements show an increase in Curie temperature, soft magnetic nature and effective magnetic moment suggesting strengthening of underlying magnetic interactions. As a result of mu ltiple oxidation states
of Co ions and the delocalization of electrons, rise in the conductivity is noticed. Such enhancement in conductivity and ferromagnetic ordering temperature simu ltaneously with V doping implies a strong coupling
between spin and charge degrees of freedom. To understand the underlying mechanism more clearly, different possible scenarios have been discussed. The most appropriate scenario i.e., the conversion of Co3+
ions into Co2+ ions and admixture of Co4+ ion spin states with V
5+ doping was found to be consistent with
all the experimental observations.
