铁磁流体（ferrofluid, ferrum 拉丁语 “铁” 与 fluid “流体” 两词的混成词）是一种在磁场存在时强烈极化的液体。铁磁流体由悬浮于载流体当中纳米数量级的铁磁微粒组成；其载流体通常为有机溶液或水。铁磁微粒由表面活性剂包裹以防止其因范德华力和磁力作用而发生凝聚。尽管被称为铁磁流体，但它们本身并不表现铁磁性。这是因为在外部磁场不存在的情况下，铁磁流体无法保持磁性。事实上，铁磁流体表现顺磁性，并且由于它们的高磁化率，通常被认为具有“超顺磁性”。产生铁磁流体在实际当中很难，一般要求高温及电磁浮置等条件。

A ferrofluid (portmanteau of ferromagnetic and fluid) is a liquid that becomes strongly magnetized in the presence of a magnetic field. Ferrofluid was invented in 1963 by NASA's Steve Papell as a liquid rocket fuel that could be drawn toward a pump inlet in a weightless environment by applying a magnetic field.