块体Mn $_{1.4}$ PtSn的各向异性分形磁畴图案
Anisotropic fractal magnetic domain pattern in bulk Mn$_{1.4}$PtSn
摘要：
具有$D_{2d}$对称性的四元化合物Mn $_{1.4}$ PtSn最近作为第一种已知的具有磁性反斯基尔米恩的材料引起了人们的注意，反斯基尔米恩的内部结构不同于迄今为止已知的斯基尔米恩。后者已经在许多具有手性晶体结构的磁体中发现。在之前的工作中，通过洛伦兹透射电子显微镜对薄板样品（$\sim$ 100~nm厚）进行观察，在真实空间中明确地证明了Mn $_{1.4}$ PtSn中反螺旋离子的存在。在本研究中，我们使用小角中子散射和磁力显微镜进行倒易和实空间成像的大块Mn $_{1.4}$ PtSn单晶在不同的温度和在施加的磁场的磁织构。我们发现，在散装的磁性织构显着不同的薄板样品。而不是自旋螺旋或antistkyrmion晶格，我们观察到一个各向异性的分形磁图案的封闭域在零场以上的自旋重取向转变温度，这转化为一组气泡域在高场。在自旋重取向转变温度以下，零场下强的面内各向异性和分形自亲和性逐渐丧失，而高场下气泡畴的形成仍然稳健。我们的研究结果强调了薄板样品中偶极-偶极相互作用对于稳定反skyrmion的重要性，并确定了指导寻找潜在（反）skyrmion宿主材料的标准。此外，他们提供了一致的解释，以前报道的大块晶体的磁输运异常。
英文摘要：
The tetragonal compound Mn$_{1.4}$PtSn with the $D_{2d}$ symmetry recently attracted attention as the first known material that hosts magnetic antiskyrmions, which differ from the so far known skyrmions by their internal structure. The latter have been found in a number of magnets with the chiral crystal structure. In previous works, the existence of antiskyrmions in Mn$_{1.4}$PtSn was unambiguously demonstrated in real space by means of Lorentz transmission electron microscopy on thin-plate samples ($\sim$100~nm thick). In the present study, we used small-angle neutron scattering and magnetic force microscopy to perform reciprocal- and real-space imaging of the magnetic texture of bulk Mn$_{1.4}$PtSn single-crystals at different temperatures and in applied magnetic field. We found that the magnetic texture in the bulk differs significantly from that of thin-plate samples. Instead of spin helices or an antiskyrmion lattice, we observe an anisotropic fractal magnetic pattern of closure domains in zero field above the spin-reorientation transition temperature, which transforms into a set of bubble domains in high field. Below the spin-reorientation transition temperature the strong in-plane anisotropy as well as the fractal self-affinity in zero field is gradually lost, while the formation of bubble domains in high field remains robust. The results of our study highlight the importance of dipole-dipole interactions in thin-plate samples for the stabilization of antiskyrmions and identify criteria which should guide the search for potential (anti)skyrmion host materials. Moreover, they provide consistent interpretations of the previously reported magnetotransport anomalies of the bulk crystals.
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