Magnetostructural Coupling at the Néel point in YNiO3 Single Crystals
Dariusz J. Gawryluk, Y. Maximilian Klein, Rebecca Scatena, Tian Shang, Romain Sibille, Denis Sheptyakov, Nicola Casati, Anthony Linden, Dmitry Chernyshov, Miros… 展开作者
Dariusz J. Gawryluk, Y. Maximilian Klein, Rebecca Scatena, Tian Shang, Romain Sibille, Denis Sheptyakov, Nicola Casati, Anthony Linden, Dmitry Chernyshov, Mirosław Kozłowski, Piotr Dłużewski, Marta D. Rossell, Piero Macchi, Marisa Medarde
The recent discovery of superconductivity in infinite layer thin films and bulk Ruddlesden-Popper nickelates has stimulated the investigation of other predicted properties of these materials. Among them, the existence of magnetism-driven ferroelectricity in the parent compounds RNiO3 (R = 4f lanthanide and Y) at the onset of the Néel order, TN, has remained particularly elusive. Using diffraction techniques, we reveal here the existence of magnetostriction at TN in bulk YNiO3 single crystals. Interestingly, the associated lattice anomalies are much more pronounced along the b crystal axis, which coincides with the electric polarization direction expected from symmetry arguments. This axis undergoes an abrupt contraction below TN that reaches deltab/b ~ - 0.01 %, a value comparable to those found in some magnetoresistive manganites and much larger than those reported for magnetism-driven multiferroics. This observation suggests a strong spin-lattice coupling in these materials, consistent with theoretical predictions. Using the symmetry-adapted distortion mode formalism we identify the main ionic displacements contributing to the lattice anomalies and discuss the most likely polar displacements below TN. Furthermore, our data support symmetric superexchange as the most likely mechanism responsible for the magnetoelastic coupling. These results, that may be common to the full RNiO3 family, provide new experimental evidence supporting the predicted existence of magnetism-driven ferroelectricity in RNiO3 perovskites
Effects of magnetic field and twin domains on magnetostructural phase mixture in Mn3O4: Raman scattering studies of untwinned crystals
亚铁磁性尖晶石Mn 3 O 4在外加磁场的作用下，其电子和结构性质发生了各向异性的变化。这些变化被认为是由于磁场依赖的调谐-通过强自旋晶格耦合-两个近简并的磁结构相之间。最近的可变磁场的Mn 3 O 4的研究已经进行了熔融生长的晶体，它可以表现出双晶域由于Jahn-Teller结构转变低于熔化温度。然而，由于磁结构相的近简并性，与孪晶畴相关的应变可能会影响Mn 3 O 4的磁响应。在这份报告中，我们提出了一个可变的磁场拉曼散射研究的非孪晶Mn 3 O 4晶体生长出的流量低于Jahn-Teller结构转变。我们测量不同的q = 0的磁性和振动激发光谱为每个孤立的非孪晶Mn 3 O 4晶体的磁结构相，并确定所观察到的激发的对称性。我们确定如何磁结构相混合物的变化响应于磁场施加在磁易平面。最后，通过比较结果通量和熔体生长的Mn 3 O 4晶体，我们表明，两个磁结构相的固有混合物确实强烈影响的存在下的孪晶域。
Field driven magnetostructural transitions in GeCo$_2$O$_4$
在尖晶石化合物GeCo $_2$ O $_4$中，Co $^{2+}$烧绿石亚晶格表现出显著的磁场诱导行为，我们通过中子和X射线单晶衍射揭示了这一点。Néel有序磁相是通过立方对称性的结构降低而进入的。在该阶段，当沿2重立方方向施加磁场时，四分之一的磁矩的自旋翻转转变释放磁阻挫并触发磁结构效应。在高磁场下，这些最终导致与结构变化相关的不寻常的自旋重定向。
Acoustic study for dynamical molecular-spin state without undergoing magnetic phase transition in spin-frustrated ZnFe$_2$O$_4$
在300 K至2 K温度范围内对自旋受抑铁氧体尖晶石ZnFe $_2$ O $_4$单晶进行了超声声速测量。在这种立方晶体中，所有的与结晶无关的弹性模量都表现出软化，并且随着温度的降低而具有特征最小值，低于$\sim$ 100 K。这种弹性异常表明动态晶格变形和分子自旋激发之间的耦合。与此相反，弹性异常，通常由磁结构相变及其前体驱动，是不存在的ZnFe $_2$ O $_4$，这表明自旋-晶格耦合不能发挥作用，在此化合物内缓解挫折。本研究推断，对于ZnFe $_2$ O $_4$，动态分子自旋态的演变在低温下没有经历前体自旋晶格涨落和自旋晶格有序。ZnFe $_2$ O $_4$提供了独特的动态自旋-晶格类液体系统，其中不仅自旋分子而且立方晶格在空间和时间上都发生了波动。
Violation of the Curie law in Na2V3O7 as the crystal-field and spin-orbit coupling effect
我们已经表明，在Na 2 V3 O 7中观察到的Curie-Weiss定律的严重违反，在Phys. Rev. Lett. 90（2003）167202，是由常规的晶体场相互作用和V4+离子的原子内自旋轨道耦合引起的。精细离散的电子结构的3d 1配置，与大量的轨道时刻，是异常的低温性能的Na 2 V3 O 7的原因。根据量子原子固态理论（QUASST），Na 2 V3 O 7在低温下会表现出明显的重费米子现象。这一研究证实了我们早先的主张，即在描述3d原子化合物时，轨道矩必须是非猝灭的。PACS：71.70.E，75.10.D关键词：晶场相互作用，自旋轨道耦合，轨道矩，Na 2 V3 O 7
