<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>q</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow></mml:math> long-range magnetic order in centennialite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CaCu</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi>OD</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Cl</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>·</mml:mo><mml:mn>0.6</mml:mn><mml:msub><mml:mi mathvariant="normal">D</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>: A spin-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac></mml:math> perfect kagome antiferromagnet with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>J</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo>−</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>−</mml:mo><mml:msub><mml:mi>J</mml:mi><mml:mi>d</mml:mi></mml:msub></mml:mrow></mml:math>
Kazuki Iida, Hiroyuki Yoshida, A. Nakao, Harald O. Jeschke, Yasir Iqbal, Kenji Nakajima, Seiko Ohira‐Kawamura, Koji Munakata, Yasuhiro Inamura, Naoki Murai, M. Ishikado, Reiji Kumai, Takuya Okada, M. Oda, Kazuhisa Kakurai, Masaaki Matsuda
Abstract
Crystal and magnetic structures of the mineral centennialite ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ are investigated by means of synchrotron x-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ crystallizes in the $P\overline{3}m1$ space group and ${\mathrm{Cu}}^{2+}$ ions form a geometrically perfect kagome network with antiferromagnetic ${J}_{1}$. No intersite disorder between ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Ca}}^{2+}$ ions is detected. ${\mathrm{CaCu}}_{3}{(\mathrm{OH})}_{6}{\mathrm{Cl}}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}0.6{\mathrm{H}}_{2}\mathrm{O}$ enters a magnetic long-range ordered state below ${T}_{\text{N}}=7.2$ K, and the $\mathbf{q}=\mathbf{0}$ magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3 K is suppressed to $0.58(2){\ensuremath{\mu}}_{\text{B}}$. Our DFT calculations indicate the presence of antiferromagnetic ${J}_{2}$ and ferromagnetic ${J}_{d}$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$\frac{1}{2}$ PFFRG analysis shows a dominance of $\mathbf{q}=\mathbf{0}$ type magnetic correlations, consistent with and indicating proximity to the observed $\mathbf{q}=\mathbf{0}$ spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a ${J}_{1}\ensuremath{-}{J}_{2}\ensuremath{-}{J}_{d}$ kagome antiferromagnet.