Spin dynamics and unconventional magnetism in insulating La(1−2x)Sr2xCo(1−x)NbxO3

Rishabh Shukla, Anil Jain, M. Miryala, M. Murakami, K. Ueno, S. M. Yusuf, R. S. Dhaka

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We study the structural, magnetic, transport and electronic properties of LaCoO3 with Sr/Nb co-substitution, i.e., La(1−2x)Sr2xCo(1−x)NbxO3 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 R¯3c) in Rietveld refinement analysis. The calculated effective magnetic moment (≈3.85 µB) and average spin (≈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 ≈50:50, i.e., spin-state of Co3+ 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 ±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 T0, 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 ≈1022 eV1cm3 and low activation energy ≈130 meV are found in x = 0.05 sample. Using x-ray photoemission spectroscopy, we study the core-level spectra of La 3d, Co 2p, Sr 3d, and Nb 3d to confirm the valence state.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2019 Jun 9

ASJC Scopus subject areas

  • General

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