Emergent antiferromagnetic transition in hyperkagome manganese ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$

We have successfully synthesized a hyperkagome antiferromagnet ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$ by a topochemical method, where ${\mathrm{Mn}}^{4+}$ ions with $S=3/2$ spins form a three-dimensional (3D) corner-sharing triangle network. Magnetic susceptibility and heat capacity measurements revealed an antiferromagnetic transition at $T_{\mathrm{N}}=5.8\mathrm{K}$. Although no evidence was found for any structural distortion accompanying the transition, the low-temperature magnetic heat capacity showed a nearly $T^2$ dependence, suggesting the realization of a 2D magnonlike excitation in the 3D hyperkagome lattice.

Figure 1

Crystal structure of (a) ${\mathrm{Li}}_2\mathrm{Zn}{\mathrm{Mn}}_3{\mathrm{O}}_8$ and (b) ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$ with the space group $P{4}_{3}32$, illustrated by vesta [22]. Purple and green octahedra represent $\mathrm{Mn}{\mathrm{O}}_6$ and $\mathrm{Li}{\mathrm{O}}_6$, and gray tetrahedra represent $\left(\mathrm{Li}/\mathrm{Zn}\right){\mathrm{O}}_4$ or $\mathrm{Zn}{\mathrm{O}}_4$. Network of ions in octahedral sites in (c) ${\mathrm{Li}}_2\mathrm{Zn}{\mathrm{Mn}}_3{\mathrm{O}}_8$ and (d) ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$. From ${\mathrm{Li}}_2\mathrm{Zn}{\mathrm{Mn}}_3{\mathrm{O}}_8$ to ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$, Li ions at the octahedral sites are replaced by vacancies, and the tetrahedral sites are occupied only by Zn ions. Accordingly, a corner-sharing tetrahedral network of Li and Mn ions in ${\mathrm{Li}}_2\mathrm{Zn}{\mathrm{Mn}}_3{\mathrm{O}}_8$ changes to a corner-sharing triangular network, that is, a hyperkagome lattice in ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$.

Figure 2

Powder x-ray diffraction pattern of (a) ${\mathrm{Li}}_2\mathrm{Zn}{\mathrm{Mn}}_3{\mathrm{O}}_8$ and (b) ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$ at room temperature. Red dots are experimental data, and green vertical bars indicate the positions of Bragg reflections. The green line on the data shows a calculated pattern with the space group $P{4}_{3}32$, and the bottom blue line shows the difference between the experimental and calculated intensities.

Figure 3

(a) Temperature dependence of the magnetic susceptibility χ under fields of 0.01, 0.1, and 1 T. The χ curves measured at 0.01 and 0.1 T are shifted for clarity. (b) Temperature dependence of the inverse magnetic susceptibility ${\chi }^{-1}$ under 0.01 T, where the solid line indicates a Curie-Weiss fit. (c) Magnetization vs applied magnetic field for ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$ measured at 4.2 K.

Figure 4

(a) Magnetic heat capacity $C_m$ of ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$, estimated by subtracting the lattice heat capacity calculated by scaling $C_p$ of ${\mathrm{Zn}}_2{\mathrm{Ge}}_3{\mathrm{O}}_8$ from the $C_p$. The inset displays the power-law behavior of $C_m$. (b) Magnetic entropy of ${\mathrm{Zn}}_2{\mathrm{Mn}}_3{\mathrm{O}}_8$. The horizontal broken line corresponds to $S_m=3R\ln 4$, which is expected for a fully ordered $S=3/2$ system.

Figure 5

(a) Temperature evolution of the low-temperature powder x-ray diffraction pattern at the high angle side, ranging from 10 to 4 K in 1-K increments. (b) Temperature dependences of full width at half maximum (FWHM) for selected diffraction peaks.