PROBLEM TO BE SOLVED: To provide a ferrofluid 1 with low in cost and high in safety, having viscosity characteristics that do not change over a long term even when an environment-friendly material is used, excellent in dispersion stability, and capable of maintaining stable magnetic characteristics.SOLUTION: A ferrofluid 1 is the ferrofluid containing magnetic particles 11 and fine plural oxidized cellulose 12. The fine plural oxidized cellulose 12 are obtained by being oxidized with at least an N-oxyl compound. The number average short axis diameter of short axes of the fine plural oxidized cellulose 12 is 1 nm or more and 200 nm or less, and the number average long axis diameter of long axes of the fine plural oxidized cellulose 12 is 0.05 μm or more and 50 μm or less.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2017,JPO&INPIT【課題】低コストで、安全性が高く、環境調和型材料を用いても長期間にわたり粘度特性が変化せず、分散性安定性に優れ、安定した磁気特性を維持できる磁性流体1を提供すること。【解決手段】磁性粒子11と微細酸化セルロース12とを含む磁性流体であり、前記微細酸化セルロース12が少なくともN-オキシル化合物を用いて酸化されて得られたことを特徴とする磁性流体。微細酸化セルロース12の短軸の数平均短軸径は、1nm以上200nm以下、微細酸化セルロース12の長軸の数平均長軸径は0.05μm以上50μm以下とした磁性流体1。【選択図】図1
