Pomjakushina Ekaterina, Pomjakushin Vladimir, Rolfs Katharina, Karpinski Janusz, Conder Kazimierz
Laboratory for Developments and Methods, Paul Scherrer Institut (PSI) , 5232 Villigen, Switzerland.
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut (PSI) , 5232 Villigen, Switzerland.
Inorg Chem. 2015 Sep 21;54(18):9092-7. doi: 10.1021/acs.inorgchem.5b01498. Epub 2015 Sep 2.
In this work, we present a new chemical route to synthesize Tm2Mn2O7 pyrochlore, which a compound that is thermodynamically unstable at ambient pressure. Differently from the reported in the past high-pressure synthesis of the same compound applying oxides as starting materials, we have obtained a pure Tm2Mn2O7 phase by a converting TmMnO3 at 1100 °C and an oxygen pressure of 1300 bar. The studies of Tm2Mn2O7 performed by a high-resolution neutron powder diffraction have shown that a pure pyrochlore cubic phase Tm2Mn2O7 (space group Fd3¯m) have been obtained. Upon cooling below 25 K, there is a transition to a ferromagnetically (FM) ordered phase observed with an additional antiferromagnetic (AFM) canting, suggesting a lowering of the initial cubic crystal symmetry. The magnetic transition is accompanied by a small but very visible magnetostriction effect. Using symmetry analysis, we have found a solution for the AFM structure in the maximal Shubnikov subgroup I41/am'd'.
在这项工作中，我们提出了一种合成Tm2Mn2O7烧绿石的新化学路线，该化合物在常压下是热力学不稳定的。与过去报道的以氧化物为起始原料高压合成该化合物不同，我们通过在1100°C和1300巴氧气压力下将TmMnO3转化，获得了纯的Tm2Mn2O7相。通过高分辨率中子粉末衍射对Tm2Mn2O7进行的研究表明，已获得纯的烧绿石立方相Tm2Mn2O7（空间群Fd3¯m）。冷却至25 K以下时，观察到向铁磁（FM）有序相的转变，并伴有额外的反铁磁（AFM）倾斜，这表明初始立方晶体对称性降低。磁转变伴随着一个小但非常明显的磁致伸缩效应。通过对称性分析，我们在最大舒布尼科夫子群I41/am'd'中找到了AFM结构的解决方案。
