Magnetic and structural properties of La 1 − x Gd x CoO 3 compounds

Highlights: • Structural and magnetic properties of La${}_{1-x}$Gd${}_x$CoO${}_3$ compounds were studied. • Antiferromagnetic interaction between magnetic moments of Gd ions is revealed. • Co magnetic state excitation energy grows strongly in La${}_{1-x}$Gd${}_x$CoO${}_3$ with Gd content. • LS to IS transition of Co spin state with temperature is expected for low Gd content. • Criterion is proposed for spin crossover type of Co ions in La${}_{1-x}$R${}_x$CoO${}_3$ compounds. We present a study of magnetic and structural properties of La${}_{1-x}$Gd${}_x$CoO${}_3$ compounds with $x=0$, 0.2, 0.5 and 1. The Gd term in magnetic susceptibility obeys the Curie–Weiss law with antiferromagnetic interaction between the magnetic moments of Gd${}^{3+}$ ions. The value of the paramagnetic Curie temperature $\Theta$ is proportional to Gd content and for GdCoO${}_3$ it reaches $\Theta \simeq -5.5$ K. The Co contribution, ${\chi }_{\mathrm{Co}}\left(T\right)$, derived by subtracting the Gd term from the total susceptibility, shows a non-monotonous behavior which is originated by the temperature induced transition of Co${}^{3+}$ ions from the ground low spin state to a higher spin state separated by an energy $\Delta$. The revealed strong increase in $\Delta$ with increasing Gd content is presumably due to the manifestation of a chemical pressure upon replacing La with Gd having a smaller ionic size.