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arXiv 2402.00558cond-mat.mes-hall
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纳米颗粒中Dzyaloshinskii-Moriya相互作用的中子散射特征

Neutron-scattering signature of the Dzyaloshinskii-Moriya interaction in nanoparticles

Evelyn Pratami Sinaga, Michael P. Adams, Eddwi H. Hasdeo, Andreas Michels

AI总结:

本研究通过微磁模拟探究FeGe纳米颗粒中Dzyaloshinskii-Moriya相互作用(DMI)的中子散射特征,发现手性函数仅在纳入DMI时非零,并给出小磁场下DMI诱导自旋调制的解析关联函数。

摘要:

反对称的Dzyaloshinskii-Moriya相互作用(DMI,Dzyaloshinskii-Moriya相互作用)存在于具有破缺反演对称性和强自旋轨道耦合的体系中。与各向同性对称交换相互作用、磁各向异性、偶极相互作用以及外加磁场共同作用时,DMI可支持并稳定多种复杂的介观磁结构的形成,例如螺旋磁结构、自旋螺旋、斯格明子或霍普夫子。在此背景下,一个重要的问题是DMI的中子散射特征,尤其是在纳米颗粒组装体中,相关的磁散射信号具有漫散射性质,而非例如在B20化合物中观测到的单晶衍射峰类型。我们利用微磁模拟研究了球形FeGe纳米颗粒中的DMI对随机平均磁中子散射可观测量的影响,具体而言是对自旋翻转小角中子散射截面、相关的手性函数以及对距离分布函数的影响。在我们研究的粒径($60 \mathrm{nm} \leq L \leq 200 \mathrm{nm}$)和外加磁场($-1 \mathrm{T} \leq μ_0 H_0 \leq 1 \mathrm{T}$)参数空间内,我们发现仅当模拟中纳入DMI时,手性函数才不为零。我们结合磁化强度傅里叶分量的对称性以及空间反演下相关能量的性质对这一结果进行了讨论。最后,针对小外加磁场的情况,我们提出了一种易于实现的解析关联函数,用于描述DMI诱导的自旋调制(波矢为$k_{\mathrm{d}}$)。对应的随机平均自旋翻转SANS截面重现了数值模拟中发现的主要特征。

英文摘要:

The antisymmetric Dzyaloshinkii-Moriya interaction (DMI) arises in systems with broken inversion symmetry and strong spin-orbit coupling. In conjunction with the isotropic and symmetric exchange interaction, magnetic anisotropy, the dipolar interaction, and an externally applied magnetic field, the DMI supports and stabilizes the formation of various kinds of complex mesoscale magnetization configurations, such as helices, spin spirals, skyrmions, or hopfions. A question of importance in this context addresses the neutron-scattering signature of the DMI, in particular in nanoparticle assemblies, where the related magnetic scattering signal is diffuse in character and not of the single-crystal diffraction-peak-type, as it is e.g.\ seen in the B20 compounds. Using micromagnetic simulations we study the effect of the DMI in spherical FeGe nanoparticles on the randomly-averaged magnetic neutron scattering observables, more specifically on the spin-flip small-angle neutron scattering cross section, the related chiral function, and the pair-distance distribution function. Within the studied parameter space for the particle size ($60 \, \mathrm{nm} \leq L \leq 200 \, \mathrm{nm}$) and the applied magnetic field ($-1 \, \mathrm{T} \leq μ_0 H_0 \leq 1 \, \mathrm{T}$), we find that the chiral function is only nonzero when the DMI is taken into account in the simulations. This result is discussed within the context of the symmetry properties of the magnetization Fourier components and of the involved energies under space inversion. Finally, for small applied magnetic fields, we provide an easy-to-implement analytical correlation function for the DMI-induced spin modulations (with wave vector $k_{\mathrm{d}}$). The corresponding randomly-averaged spin-flip SANS cross section reproduces the main features found in the numerical simulations.

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