Barnett effect in ferrofluids

埋田 真樹 ; 中堂 博之 ; 今井 正樹  ; 松尾 衛; 佐藤 奈々   ; 前川 禎通*; 齊藤 英治

Umeda, Maki; Chudo, Hiroyuki; Imai, Masaki; Matsuo, Mamoru; Sato, Nana; Maekawa, Sadamichi*; Saito, Eiji

Gyromagnetic effects can relate motions including rotation and vibration with the magnetic moment and currently gain renewed attention due to the potential applications in micro-electromechanical systems (MEMS). The Barnett effect is one of the gyromagnetic phenomena in which an object is magnetized when it is rotated. Precise measurement of the inertial field acting on an electron, i.e. Barnett field , allows us to obtain not only the gyromagnetic properties of electron spin but also the angular velocity of the rotated samples in solid and liquid states. Here we present the first observation of the Barnett effect in ferrofluids. Ferrofluid is a novel kind of functional material with a stable colloidal suspension of fine particles in a liquid solvent that exhibits both magnetic and fluid properties. Magnetic measurement shows contained FeO fine particles are super-paramagnetic and have large magnetic susceptibility, whose property is suitable for the measurement of the Barnett effect. By rotating the ferrofluid at high speed up to 1.8 kHz we found that arises with almost twice larger the magnitude than that in a solid state as shown in Figure 1. The result at low temperatures suggests that the enhancement of is due to the Brownian motion of the fine particles. We discuss the details of this enhancement in relation to fluid dynamics and an inertial force with additional results.