Anomalous magnetic and spin glass behavior in Nb-substituted LaCo1−xNbxO3


We report the structural, magnetic, transport, and electronic properties of Nb-substituted LaCo1-xNbxO3(x=0–0.2). The Rietveld refinement of x-ray diffraction data demonstrate structural phase transitions from rhombohedral to orthorhombic and further to monoclinic with increasing the Nb concentration up to x≥0.2. Interestingly, we observed dramatic changes in the magnetization (M) with increasing the Nb concentration, as the M sharply increases below 10 K even at 2.5% substitution. Furthermore, ac susceptibility data show the spin glass behavior in x=0.1 sample. We find that the density of states near the Fermi level decreases and the activation energy increases, which results in the decreasing conductivity with higher Nb concentration. A significant shift in the peak position of A2g phonon mode has been observed using Raman spectroscopy, which indicates the change in the coupling due to the structural distortion with Nb substitution. The core-level photoemission study confirms that the Nb is present in 5+ valence state. Our study reveals that the nonmagnetic Nb 5+(d0) substitution converts Co 3+ions to Co 2+ and stabilizes both in the high-spin state. Our results suggest that structural and spin-state transitions as well as the difference in the ionic radii between Nb 5+ and Co 3+ are playing an important role in tuning the physical properties.

Contact details: 

Prof. Rajendra S. Dhaka

Department of Physics