Spin dynamics and unconventional magnetism in insulating La${}_{(1-2x)}$Sr${}_{2x}$Co${}_{(1-x)}$Nb${}_x$O${}_3$

Abstract

We study the structural, magnetic, transport and electronic properties of LaCoO${}_3$ with Sr/Nb co-substitution, i.e., La${}_{(1-2x)}$Sr${}_{2x}$Co${}_{(1-x)}$Nb${}_x$O${}_3$ using x-ray and neutron diffraction, dc and ac-magnetization, neutron depolarization, dc-resistivity and photoemission measurements. The powder x-ray and neutron diffraction data were fitted well with the rhombohedral crystal symmetry (space group \textit{R$\bar{3}$c}) in Rietveld refinement analysis. The calculated effective magnetic moment ($\approx$3.85~${\mu }_B$) and average spin ($\approx$1.5) of Co ions from the analysis of magnetic susceptibility data are consistent with 3+ state of Co ions in intermediate-spin (IS) and high-spin (HS) states in the ratio of $\approx$50:50, i.e., spin-state of Co${}^{3+}$ is preserved at least up to $x=$ 0.1 sample. Interestingly, the magnetization values were significantly increased with respect to the $x=$ 0 sample, and the M-H curves show non-saturated behavior up to an applied maximum magnetic field of $\pm$70 kOe. The ac-susceptibility data show a shift in the freezing temperature with excitation frequency and the detailed analysis confirm the slower dynamics and a non-zero value of the Vogel-Fulcher temperature T${}_0$, which suggests for the cluster spin glass. The unusual magnetic behavior indicates the presence of complex magnetic interactions at low temperatures. The dc-resistivity measurements show the insulating nature in all the samples. However, relatively large density of states $\approx$10${}^{22}$ eV${}^{-1}$cm${}^{-3}$ and low activation energy $\approx$130~meV are found in $x=$ 0.05 sample. Using x-ray photoemission spectroscopy, we study the core-level spectra of La 3$d$, Co 2$p$, Sr 3$d$, and Nb 3$d$ to confirm the valence state.

arXiv commentsubmitted

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Cited by in corpus (6)

• Unraveling the magnetic interactions and spin state in insulating Sr${}_{2-x}$La${}_x$CoNbO${}_6$
• Evidence of discrete energy states and cluster-glass behavior in Sr${}_{2-x}$La${}_x$CoNbO${}_6$
• Structural, transport, optical and electronic properties of Sr${}_2$CoNbO${}_6$ thin films
• Evolution of complex magnetic phases and metal-insulator transition through Nb substitution in La${}_{0.5}$Sr${}_{0.5}$Co${}_{1-x}$Nb${}_x$O${}_3$
• Structural and transport properties of La${}_{1-x}$Sr${}_x$Co${}_{1-y}$Nb${}_y$O${}_3$ thin films
• X-ray Absorption Spectroscopy Study of La${}_{1-y}$Sr${}_y$Co${}_{1-x}$Nb${}_x$O${}_3$