Institut Laue Langevin, Diffraction Group BP 156, 6 rue Jules Horowitz, F-38042 Grenoble Cedex 9, France.
Inorg Chem. 2013 Aug 19;52(16):9627-35. doi: 10.1021/ic401408f. Epub 2013 Aug 1.
The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW-type material have been studied by temperature-dependent neutron powder diffraction, low-temperature magnetometry, and heat capacity measurements. RbMnPO4 represents a rare example of a weak ferromagnetic polar material, containing Mn(2+) ions with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K shows that the compound crystallizes in the chiral and polar monoclinic space group P2(1) (No. 4) with the unit cell parameters: a = 8.94635(9), b = 5.43415(5), and c = 9.10250(8) Å and β = 90.4209(6)°. A close inspection of the crystal structure of RbMnPO4 shows that this material presents two different types of zigzag chains running along the b axis. This is a unique feature among the zeolite-ABW-type materials exhibiting the P2(1) symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic structure characterized by the propagation vector k1 = 0, resulting in the magnetic symmetry P2(1)'. The magnetic moments lie mostly along the b axis with the ferromagnetic component being in the ac plane. Due to the geometrical frustration present in this system, an intermediate phase appears within the temperature range 4.7-5.1 K characterized by the propagation vector k2 = (kx, 0, kz) with kx/kz ≈ 2. This ratio is reminiscent of the multiferroic phase of the orthorhombic RMnO3 phases (R = rare earth), suggesting that RbMnPO4 could present some multiferroic properties at low temperature. Our density functional calculations confirm the presence of magnetic frustration, which explains this intermediate incommensurate phase. Taking into account the strongest magnetic interactions, we are able to reproduce the magnetic structure observed experimentally at low temperature.
通过温度依赖的中子粉末衍射、低温磁强计和热容测量研究了 RbMnPO4 沸石-ABW 型材料的晶体结构和磁性。RbMnPO4 代表了一种罕见的弱铁磁极性材料，其中含有 TN = 4.7 K 的 Mn(2+)离子。在 T = 10 K 下记录的中子粉末衍射图谱表明，该化合物在手性和极性单斜空间群 P2(1)（No. 4）中结晶，具有单位晶胞参数：a = 8.94635(9)，b = 5.43415(5)，c = 9.10250(8)Å 和 β = 90.4209(6)°。仔细观察 RbMnPO4 的晶体结构表明，该材料呈现出两种不同类型的沿 b 轴运行的锯齿链。这是在具有 P2(1)对称性的沸石-ABW 型材料中一个独特的特征。在低温下，RbMnPO4 表现出由传播矢量 k1 = 0 确定的倾斜反铁磁结构，导致磁对称 P2(1)’。磁矩主要沿着 b 轴，铁磁分量在 ac 平面内。由于该系统中存在几何上的挫败感，在 4.7-5.1 K 的温度范围内出现了一个中间相，其传播矢量为 k2 = (kx,0,kz)，其中 kx/kz ≈ 2。这个比值让人想起正交 RMnO3 相（R = 稀土）的多铁相，表明 RbMnPO4 在低温下可能具有一些多铁性能。我们的密度泛函计算证实了磁挫败感的存在，这解释了这种中间失谐相。考虑到最强的磁相互作用，我们能够再现低温下实验观察到的磁结构。
