Evidence of discrete energy states and cluster-glass behavior in Sr${}_{2-x}$La${}_x$CoNbO${}_6$

Abstract

We report the detailed analysis of specific heat [C${}_{\mathrm{P}}$(T)] and ac-susceptibility for magnetically frustrated Sr${}_{2-x}$La${}_x$CoNbO${}_6$ ($x=$ 0--1) double perovskites to understand low temperature complex magnetic interactions and their evolution with $x$. Interestingly, the observed Schottky anomaly in the $x⩽$ 0.4 samples shifts gradually towards higher temperature with magnetic field as well as $x$, and the analysis reveal the persistence of the discrete energy states in these samples resulting from the spin-orbit coupling and octahedral distortion. Moreover, the extracted values of Landé g--factor indicate the existence of high-spin state Co${}^{3+}$ ions close to non-magnetic low-spin state. The specific heat data show the $\lambda$-type anomaly for the $x⩾$ 0.6 samples due to evolution of the long range antiferromagnetic ordering. Our analysis of low temperature C${}_{\mathrm{P}}$(T) data for the $x⩾$ 0.6 samples demonstrate the 3D isotropic Heisenberg antiferromagnetic (AFM) interactions and the temperature induced second order AFM--paramagnetic phase transition. More interestingly, we demonstrate the presence of the free Co${}^{2+}$ like Kramers doublet ground state in the $x=$1 sample. Further, the ac susceptibility and time evolution of the magnetization data reveal the low temperature cluster-glass like behavior in the $x=$ 0--0.4 samples, where spin-spin correlation strength decreases with $x$.

accepted for publication in PRB

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• Chemical tuning of a honeycomb magnet through a critical point
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• Non-trivial critical behavior at the magnetic transitions: A case study of Sm${}_7$Pd${}_3$
• X-ray Absorption Spectroscopy Study of La${}_{1-y}$Sr${}_y$Co${}_{1-x}$Nb${}_x$O${}_3$