Doping-induced structural transformation in the spin-1/2 triangular-lattice antiferromagnet Na$_{2}$Ba$_{1-x}$Sr$_{x}$Co(PO$_{4}$)$_{2}$

Chuandi Zhang; Qianhui Xu; Xu-Tao Zeng; Chao Lyu; Zhengwang Lin; Jiazheng Hao; Sihao Deng; Lunhua He; Yinguo Xiao; Yu Ye; Ziyu Chen; Xian-Lei Sheng; Wentao Jin

doi:10.1016/j.jallcom.2022.164147

paper

Doping-induced structural transformation in the spin-1/2 triangular-lattice antiferromagnet Na $_{2}$ Ba $_{1 - x}$ Sr $_{x}$ Co(PO $_{4}$ ) $_{2}$

arXiv:2205.08444 · doi:10.1016/j.jallcom.2022.164147

Abstract

The effects of Sr doping on the structural properties of Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$ , a spin-1/2 triangular-lattice antiferromagnet as a quantum spin liquid candidate, are investigated by complementary x-ray and neutron powder diffraction measurements. It is found that in Na $_{2}$ Ba $_{1 - x}$ Sr $_{x}$ Co(PO $_{4}$ ) $_{2}$ (NBSCPO), the trigonal phase (space group $P$ $3 ˉ$ $m$ 1) with a perfect triangular lattice of Co $^{2 +}$ ions is structurally stable when the doping level of Sr is below 30% ( $x$ $\leq$ 0.3), while a pure monoclinic phase (space group $P$ 2 $_{1}$ / $a$ ) with slight rotations of CoO $_{6}$ octahedra and displacements of Ba $^{2 +}$ /Sr $^{2 +}$ ions will be established when the Sr doping level is above 60% ( $x$ $\geq$ 0.6). Such a doping-induced structural transformation in NBSCPO is supported by first-principles calculations and Raman spectroscopy. Na $_{2}$ SrCo(PO $_{4}$ ) $_{2}$ , a novel spin-1/2 triangular-lattice antiferromagnet with glaserite-type structure, although monoclinically distorted, exhibits no long-range magnetic order down to 2 K and a similar negative Curie-Weiss temperature as Na $_{2}$ BaCo(PO $_{4}$ ) $_{2}$ with a perfect triangular lattice, suggesting the robustness of magnetic exchange interaction against the Ba/Sr substitutions.

26 pages, 7 figures

Doping-induced structural transformation in the spin-1/2 triangular-lattice antiferromagnet Na2​Ba1−x​Srx​Co(PO4​)2​

Abstract

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Doping-induced structural transformation in the spin-1/2 triangular-lattice antiferromagnet Na $_{2}$ Ba $_{1 - x}$ Sr $_{x}$ Co(PO $_{4}$ ) $_{2}$