Abstract

Polarized small-angle neutron scattering was used for studying of critical fluctuations in the Dzyaloshinskii–Moriya helimagnets Mn_{1 – x}Fe_xSi with x = 0.10, 0.15, 0.20. The Mn_{1 – x}Fe_xSi compounds are helically ordered below T_c and show a helical fluctuation regime above T_c in a wide range up to T_DM. The critical temperatures T_c and T_DM decrease with x and tend to 0 at x = 0.11 and 0.17, respectively. It was shown experimentally that three samples reveal properties of fluctuations in different regimes. The sample with x = 0.10 provides sharp narrow peak in polarized SANS maps for temperatures near T_c and in the ordered phase, whereas in the one with x = 0.15 critical fluctuations are suppressed by the disorder which destroys long-range magnetic order, corresponding scattering peaks being substantially wider than for x = 0.10. For the sample with x = 0.20 even at lowest temperatures only traces of the half-moon scattering patterns are visible. The degree of the scattering polarization is close to 1 for all three samples meaning that the corresponding helical fluctuations are chiral. The Mn_{1 – x}Fe_xSi compounds represent an example of the system where ferromagnetic exchange approaches zero but Dzyaloshinskii–Moriya interaction is finite and provides chiral rotation of spins in magnetic fluctuations. We argue at the qualitative level that observed peculiarities can be attributed to defect antiferromagnetic bonds which are added to the system by Fe ions and lead to finite correlation length of the spiral at small temperatures for x > x_c.

中文翻译：

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Dzyaloshinskii-Moriya Helimagnets Mn1 中超越量子相变的临界波动 – xFexSi

摘要

偏振小角中子散射用于研究 Dzyaloshinskii-Moriya 螺旋磁体 Mn _{1 – x} Fe _x Si的临界涨落，其中x = 0.10、0.15、0.20 。Mn的_{1 - X}的Fe _X Si类化合物被螺旋有序下面Ť _Ç，并显示上述的螺旋波动制度Ť _Ç在宽范围内达到Ť _DM。临界温度T _c和T _DM随x降低，并在x处趋于 0= 0.11 和 0.17，分别。实验表明，三个样品揭示了不同状态下的波动特性。x = 0.10的样品在T _c附近的温度和有序相的极化 SANS 图中提供了尖锐的窄峰，而在x = 0.15的样品中，临界波动被破坏远程磁序的无序抑制，相应的散射峰明显宽于x = 0.10。对于带有x的样本= 0.20 即使在最低温度下，也只能看到半月形散射图案的痕迹。所有三个样品的散射偏振度都接近于 1，这意味着相应的螺旋波动是手性的。Mn _{1 – x} Fe _x Si 化合物代表了系统的一个例子，其中铁磁交换接近于零，但 Dzyaloshinskii-Moriya 相互作用是有限的，并在磁波动中提供自旋的手性旋转。我们在定性水平上认为，观察到的特性可归因于缺陷反铁磁键，Fe 离子将其添加到系统中，并导致x > x _c在小温度下螺旋的有限相关长度。