Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field.
Magnetic Fluctuations, Precursor Phenomena, and Phase Transition in MnSi under a Magnetic Field.
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磁场下 MnSi 的磁涨落、前驱体现象和相变。
DOI：
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发表时间：
2016
影响因子：
8.6
通讯作者：
P. Falus
中科院分区：
文献类型：
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作者：
C. Pappas;L. Bannenberg;E. Lelièvre;F. Qian;C. Dewhurst;R. Dalgliesh;D. Schlagel;T. Lograsso;P. Falus
参考手性螺旋磁体 MnSi 是第一个报道斯格明子晶格关联的系统。在零磁场下，T_{C} 到螺旋磁态的转变是一阶的。在 T_{C} 以上，在前兆现象占主导地位的区域中，中子散射显示出在半径为 2π/ℓ 的球体表面上形成了强手性涨落相关性，其中 ℓ 是螺旋的螺距。有人认为，按照布拉佐夫斯基提出的液晶方案，这些波动的相关性会驱动螺旋过渡到一阶。我们提出了磁场下的全面中子散射研究，证明事实并非如此。对于高达 0.4 T 的磁场，急剧的一阶跃迁持续存在，而脉动相关性减弱并开始沿着已经高于 0.2 T 的磁场方向集中。因此，我们的结果将跃迁的一阶性质与前体脉动相关性脱节。它们也没有显示出三临界点的迹象，即随着磁场的增加，一阶跃迁跨越到二阶。有鉴于此，与手性磁性普遍相关的一阶螺旋跃迁的性质和 T_{C} 以上的前兆现象仍然是一个悬而未决的问题。
The reference chiral helimagnet MnSi is the first system where Skyrmion lattice correlations have been reported. At a zero magnetic field the transition at T_{C} to the helimagnetic state is of first order. Above T_{C}, in a region dominated by precursor phenomena, neutron scattering shows the buildup of strong chiral fluctuating correlations over the surface of a sphere with radius 2π/ℓ, where ℓ is the pitch of the helix. It has been suggested that these fluctuating correlations drive the helical transition to first order following a scenario proposed by Brazovskii for liquid crystals. We present a comprehensive neutron scattering study under magnetic fields, which provides evidence that this is not the case. The sharp first order transition persists for magnetic fields up to 0.4 T whereas the fluctuating correlations weaken and start to concentrate along the field direction already above 0.2 T. Our results thus disconnect the first order nature of the transition from the precursor fluctuating correlations. They also show no indication for a tricritical point, where the first order transition crosses over to second order with increasing magnetic field. In this light, the nature of the first order helical transition and the precursor phenomena above T_{C}, both of general relevance to chiral magnetism, remain an open question.