Crystal structure and magnetic properties of 6H-SrMnO3

Abstract

The 6$H$-SrMnO${}_{3}$ polymorph was prepared using a high-pressure and high-temperature technique at 6 GPa and 1773 K. Its crystal structure was refined using synchrotron x-ray powder diffraction data (space group $P$6${}_{3}$/mmc (no. 194), $Z$ $=$ 6, $a$ $=$ 5.42892(1) \AA{}, $c$ $=$ 13.40252(3) \AA{}). Magnetic and transport properties of 6$H$-SrMnO${}_{3}$ were investigated using direct current magnetization, specific heat, and resistivity measurements. The antiferromagnetic N\'eel temperature ${T}_{\mathrm{N}}$ of 6$H$-SrMnO${}_{3}$ is 235 K; this value is close to that of cubic-SrMnO${}_{3}$ (${T}_{\mathrm{N}}$ $=$ 240 K) and 4$H$-SrMnO${}_{3}$ (${T}_{\mathrm{N}}$ $=$ 280 K). 6$H$-SrMnO${}_{3}$ and 4$H$-SrMnO${}_{3}$ have the same building blocks of face-sharing MnO${}_{6}$ octahedra. Magnetic susceptibility of 6$H$-SrMnO${}_{3}$ exhibits behavior typical for classical three-dimensional antiferromagnets with a maximum near ${T}_{\mathrm{N}}$---in contrast to those of cubic-SrMnO${}_{3}$ and 4$H$-SrMnO${}_{3}$, where broad maxima are observed far above ${T}_{\mathrm{N}}$. Isothermal magnetization curves of 6$H$-SrMnO${}_{3}$ (at 2 K) show an upturn deviation from the linear behavior above 10 kOe, indicating a possible spin--flop magnetic phase transition.