Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr 2 O 4
Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr 2 O 4
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近海森堡烧绿石反铁磁体 MgCr 2 O 4 中磁有序态流形和激发
DOI：
10.1103/physrevb.97.134430
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发表时间：
2018
影响因子：
3.7
通讯作者：
Gao S
中科院分区：
文献类型：
--
作者：
Gao S
在尖晶石中，经典的烧绿石海森堡反铁磁体模型的实现是复杂的强自旋-晶格耦合：广泛的基态简并解除了磁结构转变atK。我们研究了低温低对称性的晶体结构的同步辐射x射线衍射。用Escherberget的四元模型解释了低温X射线图象的一致性特征。[啪。Diff. 17，230（2002）PODIE 20885 -715610.1154/1.1479738]，而其它特征取决于样品或冷却方案。本文用中子衍射和球中子极化法研究了复杂的半有序磁态。传播矢量的位形臂出现多个磁畴。当两相数量相等时，有序矩分别为1.94（3）和2.08（3）.磁排列具有沿着[110]和对角线的主导分量和较小的分量。我们使用非弹性中子散射调查的自旋激发，其中包括一个混合物的分散自旋波传播的磁布拉格峰和共振模式为中心，在相等的能量步骤为4.5毫电子伏。我们解释这些作为声学和光学自旋波分支，但表明，中子散射截面内的两个角共享四面体的单元内的过渡匹配所观察到的强度分布的共振。在光学自旋波分支中的团簇状激发的独特指纹表明，传播激发是由复杂的晶体结构和磁序局域化的。
In spinels, realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition atK. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberget al.[Pow. Diff. 17, 230 (2002)PODIE20885-715610.1154/1.1479738], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectorsappear. The ordered moment reaches 1.94(3)forand 2.08(3)for, if equal amount of theandphases is assumed. The magnetic arrangements have the dominant components along the [110] anddiagonals and a smallercomponent. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. The distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.