J. Stefan Institute, SI-1000 Ljubljana, Slovenia.
J. Stefan Institute, SI-1000 Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Slovenia.
Soft Matter. 2019 Jul 10;15(27):5412-5420. doi: 10.1039/c9sm00949c.
Suspensions of magnetic nanoplatelets in isotropic solvents are very interesting examples of ferrofluids. It has been shown that above a certain concentration ΦNI such suspensions form a ferromagnetic nematic phase, which makes this system a unique example of a dipolar fluid. The formation of a nematic phase is driven by anisotropic electrostatic and long-range dipolar magnetic interactions. Here, we present studies of the evolution of short range positional and orientational magnetic order in suspensions with volume fractions below and above ΦNI, using small angle neutron scattering (SANS). The results show that in the absence of an external magnetic field, short range positional and orientational order already exist at relatively low volume fractions. Polarized SANS revealed that the contribution of ferromagnetic ordering to the formation of the nematic phase is significant. The ferromagnetic correlations can be qualitatively explained by a simple model, which takes into account anisotropic screened electrostatic and dipolar magnetic interactions.
各向同性溶剂中磁性纳米板的悬浮液是铁磁流体非常有趣的例子。已经表明，高于一定浓度 ΦNI，这种悬浮液形成铁磁向列相，这使得该系统成为偶极流体的独特示例。向列相的形成是由各向异性静电和长程偶极磁相互作用驱动的。在这里，我们使用小角中子散射 (SANS) 研究了体积分数低于和高于 ΦNI 的悬浮液中短程位置和取向磁序的演变。结果表明，在没有外磁场的情况下，短程位置和取向序在相对较低的体积分数下就已经存在。偏振 SANS 表明，铁磁有序对向列相形成的贡献是显著的。铁磁相关性可以通过一个简单的模型定性解释，该模型考虑了各向异性屏蔽静电和偶极磁相互作用。
