Short-range correlations and persistent spin fluctuations in the undistorted kagome lattice Ising antiferromagnet Co${}_{3}$Mg(OH)${}_{6}$Cl${}_{2}$

Short-range correlations and persistent spin fluctuations in the undistorted kagome lattice Ising antiferromagnet Co $_{3}$ Mg(OH) $_{6}$ Cl $_{2}$

M. Fujihala, X. G. Zheng, Y. Oohara, H. Morodomi, T. Kawae, Akira Matsuo, and Koichi Kindo

Phys. Rev. B 85, 012402 – Published 10 January 2012

Abstract

Spin fluctuations and spin-liquid behaviors of frustrated kagome antiferromagnets have received intense recent attention. Although most severe frustration was predicted for an Ising kagome antiferromagnet, a real material system of undistorted kagome lattice has not been found so far. Here we report the frustrated magnetism of a new Ising kagome antiferromagnet, MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ , which can be viewed as a Co version of the intensively researched quantum kagome antiferromagnet of Herbertsmithite ZnCu $_{3}$ (OH) $_{6}$ Cl $_{2}$ . Experiments of magnetization, heat capacity, μSR, and neutron scattering demonstrated a partially frozen state with persistent spin fluctuations below around $T$ = 2.7 K. The present study has provided a real material system to study the Ising spin behaviors on undistorted kagome lattice.

Received 9 December 2011

DOI:https://doi.org/10.1103/PhysRevB.85.012402

Authors & Affiliations

M. Fujihala¹, X. G. Zheng^1,2,*, Y. Oohara³, H. Morodomi⁴, T. Kawae⁴, Akira Matsuo⁵, and Koichi Kindo⁵

¹Department of Physics, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan
²Department of Physics, Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan
³Neutron Science Laboratory, Institute for Solid State Physics, The University of Tokyo, Shirakata 106-1, Tokai 319-1106, Japan
⁴Department of Applied Quantum Physics, Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan
⁵International MegaGauss Science Laboratory, Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581, Japan

^*zheng@cc.saga-u.ac.jp

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Vol. 85, Iss. 1 — 1 January 2012

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Images

Figure 1
The observed synchrotron x-ray diffraction intensity pattern (filled red circles) for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ at room temperature and the result of the calculated Rietveld structure refinements shown by the grey solid line and the difference between the calculated and observed intensities (blue solid line below the XRD spectra). The green vertical bars indicate the position of Bragg reflection peaks. The inset shows a schematic view of the crystal structure for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ , where the triangular-lattice-plane ions are replaced by Mg $^{2 +}$ (white balls) and the Co $^{2 +}$ (black balls) form a perfect kagome lattice.Reuse & Permissions
Figure 2
(a) Temperature dependence of the dc susceptibilities χ (open red circles, left axis) and their inverse susceptibilities 1/χ (open green squares, right axis) per mole Co measured at 10 kOe for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ . The thick grey line obeys the Curie-Weiss law, χ $^{- 1}$ ( $T$ ) = ( $T - θ_{CW}$ )/ $C$ , with a Weiss temperature θ $_{CW}$ of approximately −3.77 K. The inset plot depicts a magnetic transition near 3 K and the divergence of the magnetization curves measured at 1 kOe under field-cooling and zero-field-cooling conditions. (b) Temperature dependence of the real and imaginary parts of the ac susceptibilities $χ_{ac}^{'}$ (open red circles, left axis) and $χ_{ac}^{''}$ (open green squares, right axis), measured at various frequencies for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ . The inset plot displays the fit to a conventional dynamical scaling analysis as described in the text.Reuse & Permissions
Figure 3
Characteristics of $C_{mag}$ ( $T$ )/ $T$ under external fields of 0, 1, and 3 T, respectively, for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ . The inset plot shows the total specific heat and the magnetic entropy drop.Reuse & Permissions
Figure 4
(a) High-field magnetization for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ at typical temperatures. (b) Differential plots for $d M / d H$ versus temperature.Reuse & Permissions
Figure 5
ZF-μSR asymmetries for MgCo $_{3}$ (OH) $_{6}$ Cl $_{2}$ at typical temperatures. The solid lines represent fitted curves. The inset plot shows the LF-μSR asymmetries at 1.9 K under zero field and external fields of 100, 1000, and 2400 G.Reuse & Permissions
Figure 6
(a) Neutron diffraction intensity patterns for MgCo $_{3}$ (OD) $_{6}$ Cl $_{2}$ obtained at 20 K and 1.36 K. The inset plot shows the difference between the two intensity patterns. The solid line represents a fit of the measured data to the equation $I$ ( $Q$ ) ∼ sin( $Q R$ )/ $Q R$ with $R$ = 5.0(2). (b) Inelastic neutron scattering spectra for MgCo $_{3}$ (OD) $_{6}$ Cl $_{2}$ ; constant- $Q$ ( $Q$ = 0.9 Å $^{- 1}$ ) scans at $T$ = 0.72, 5.0, and 50 K. The thick grey line was a fit to the Lorentzian function. The inset plot shows the temperature dependence of the inelastic intensity at $Q$ = 0.9 Å $^{- 1}$ and $E$ = 0.7 meV, and the solid line therein is a guide to the eyes. (c) Inelastic neutron scattering spectra for MgCo $_{3}$ (OD) $_{6}$ Cl $_{2}$ ; constant- $Q$ scans for $Q$ = 0.6, 0.9, 1.2, and 2.0, demonstrating the independence of the energy absorption on $Q$ .Reuse & Permissions

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