Metamagnetic texture in a polar antiferromagnet
Metamagnetic texture in a polar antiferromagnet
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DOI：
10.1038/s41567-019-0501-0
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发表时间：
2018-10
期刊：
影响因子：
19.6
通讯作者：
D. Sokolov;Naoki Kikugawa;Toni Helm;H. Borrmann;Ulrich Burkhardt;R. Cubitt;Jonathan S. White;E. Ressouche;M. Bleuel;M. Bleuel;K. Kummer;A. P. Mackenzie;A. P. Mackenzie;U. Rößler
中科院分区：
文献类型：
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作者：
D. Sokolov;Naoki Kikugawa;Toni Helm;H. Borrmann;Ulrich Burkhardt;R. Cubitt;Jonathan S. White;E. Ressouche;M. Bleuel;M. Bleuel;K. Kummer;A. P. Mackenzie;A. P. Mackenzie;U. Rößler
简单有序状态的概念意味着同质性。如果序是由破缺对称建立的，则相变的基本朗道理论表明，只有一种对称模式描述这种状态。在相共存的精确点，由不同相的大区域组成的域态可以通过远程相互作用来稳定。在单轴反铁磁体中，所谓的超磁性是这种行为的一个例子，其中反铁磁和场诱导的，自旋极化的顺磁/铁磁状态在磁相图中的跳变中共存。本文通过实验与理论分析相结合，证明了在某些非中心对称材料中可以产生一种不同类型的反铁磁性和铁磁性混合态。在小角中子散射实验中，我们观察到层状反铁磁体Ca3Ru2O7的场驱动自旋态，该自旋态在8 ~ 20 nm范围内调制，同时具有反铁磁和铁磁部分。我们称这种状态为超磁织构，并将其出现归因于不对称Dzyaloshinskii-Moriya交换的手性扭转效应。这一观察结果可以理解为一种非同寻常的共存——在一种热力学状态下，属于不同对称的自旋顺序。通过对电子输运异常的测量证明了这种超磁状态的复杂性，这些异常反映了超磁织构中的自旋极化；磁轨道矩的确定，支持了强自旋轨道效应的存在，是研究这种材料中扭曲磁态机制的先决条件。我们的发现提供了一个丰富的、很大程度上未被探索的纹理状态类别的例子。这种织构在接近相共存的不同有序模式之间进行调解，产生极为丰富的相图。
The notion of a simple ordered state implies homogeneity. If the order is established by a broken symmetry, the elementary Landau theory of phase transitions shows that only one symmetry mode describes this state. At the exact points of phase coexistence, domain states composed of large regions of different phases can be stabilized by long-range interactions. In uniaxial antiferromagnets, so-called metamagnetism is an example of such behaviour where antiferromagnetic and field-induced, spin-polarized paramagnetic/ferromagnetic states coexist at a jump-like transition in the magnetic phase diagram. Here, by combining experiments with theoretical analysis, we show that a different type of mixed state between antiferromagnetism and ferromagnetism can be created in certain non-centrosymmetric materials. In small-angle neutron scattering experiments, we observe a field-driven spin state in the layered antiferromagnet Ca3Ru2O7, which is modulated on a scale between 8 and 20 nm and has both antiferromagnetic and ferromagnetic parts. We call this state a metamagnetic texture and attribute its appearance to the chiral twisting effects of the asymmetric Dzyaloshinskii–Moriya exchange. The observation can be understood as an extraordinary coexistence—in one thermodynamic state—of spin orders that belong to different symmetries. The complex nature of this metamagnetic state is demonstrated experimentally by measurements of anomalies in electronic transport that reflect the spin polarization in the metamagnetic texture; determination of the magnetic orbital moments, which support the existence of strong spin–orbit effects, is a pre-requisite for the mechanism of twisted magnetic states in this material. Our findings provide an example of a rich and largely unexplored class of textured states. Such textures mediate between different ordering modes near phase coexistence, and produce extremely rich phase diagrams.