National Institute for Materials Science, Tsukuba, Ibaraki, Japan.
Phys Rev Lett. 2012 Aug 31;109(9):097203. doi: 10.1103/PhysRevLett.109.097203. Epub 2012 Aug 27.
We have performed dielectric measurements and neutron diffraction experiments on the delafossite AgFeO2. A ferroelectric polarization P is approximately equal to 300 μC/m2 was observed in a powder sample, below 9 K. The neutron diffraction experiment demonstrated successive magnetostructural phase transitions at T(N1)=15 K and T(N2)=9 K. The magnetic structure for 9 K≤T≤15 K is a spin-density wave with a temperature dependent incommensurate modulation k=(-1, q, 1/2), q is approximately equal to 0.384. Below 9 K, the magnetic structure turns into elliptical cycloid with the incommensurate propagation vector k=(-1/2,q,1/2), q is approximately equal to 0.2026 Based on the deduced magnetic point-group symmetry m1' of the low-temperature polar phase, we conclude that the ferroelectric polarization in AgFeO2 is perpendicular to the monoclinic b axis and is driven by the inverse Dzyaloshinskii-Moriya effect with two orthogonal components p1 is proportional to r(ij)×(S(i)×S(j)) and p2 is proportional to S(i)×S(j).
我们对德拜石型的 AgFeO2 进行了介电测量和中子衍射实验。在粉末样品中，在 9 K 以下观察到约等于 300 μC/m2 的铁电极化 P。中子衍射实验证明在 T(N1)=15 K 和 T(N2)=9 K 处存在连续的磁结构相变。9 K≤T≤15 K 时的磁结构是温度相关的非共线调制的自旋密度波，q 约等于 0.384。在 9 K 以下，磁结构转变为具有非共线传播矢量 k=(-1/2,q,1/2)的椭圆旋进，q 约等于 0.2026。基于低温极相的推导磁点群对称性 m1'，我们得出 AgFeO2 中的铁电极化垂直于单斜 b 轴，由两个正交分量驱动，p1 与 r(ij)×(S(i)×S(j))成正比，p2 与 S(i)×S(j)成正比。
