Prokhnenko O, Feyerherm R, Mostovoy M, Aliouane N, Dudzik E, Wolter A U B, Maljuk A, Argyriou D N
Hahn-Meitner-Institute, Glienicker Str. 100, D-14109 Berlin, Germany.
Phys Rev Lett. 2007 Oct 26;99(17):177206. doi: 10.1103/PhysRevLett.99.177206. Epub 2007 Oct 23.
We report on diffraction measurements on multiferroic TbMnO(3) which demonstrate that the Tb- and Mn-magnetic orders are coupled below the ferroelectric transition T(FE) = 28 K. For T<T(FE) the magnetic propagation vectors (tau) for Tb and Mn are locked so that tau(Tb) = tau(Mn), while below T(N)(Tb) = 7 K we find that tau(Tb) and tau(Mn) lock-in to rational values of 3/7b* and 2/7b*, respectively, and obey the relation 3tau(Tb)-tau(Mn)=1. We explain this novel matching of wave vectors within the frustrated anisotropic next-nearest-neighbor Ising model coupled to a periodic external field produced by the Mn-spin order. The tau(Tb)=tau(Mn) behavior is recovered when Tb magnetization is small, while the tau(Tb) = 3/7 regime is stabilized at low temperatures by a peculiar arrangement of domain walls in the ordered state of Ising-like Tb spins.
我们报道了对多铁性TbMnO₃的衍射测量结果，这些结果表明，在铁电转变温度T(FE)=28K以下，Tb和Mn的磁序是耦合的。对于T<T(FE)，Tb和Mn的磁传播矢量(tau)被锁定，使得tau(Tb)=tau(Mn)，而在T(N)(Tb)=7K以下，我们发现tau(Tb)和tau(Mn)分别锁定到3/7b和2/7b的有理数值，并满足关系3tau(Tb)-tau(Mn)=1。我们在与由Mn自旋序产生的周期性外场耦合的受挫各向异性次近邻伊辛模型中解释了这种波矢的新颖匹配。当Tb磁化强度较小时，tau(Tb)=tau(Mn)的行为得以恢复，而在类伊辛Tb自旋的有序状态下，畴壁的特殊排列在低温下稳定了tau(Tb)=3/7的状态。
