Magnetic-Fluid Casimir Forces as a Probe of Low-Frequency Metal Optical Response.

We propose a magnetic-fluid-based approach that enables a decisive test of the long-standing Drude-plasma contention in Casimir physics. We investigate the interaction between a polystyrene plate and a metallic sphere, both immersed in a magnetic fluid. The plasma model predicts a reversal of the force sign over a broad range of separations for different types of magnetic fluids, in contrast to the Drude model. This qualitative effect offers a reliable and experimentally testable approach to resolving the optical-model dispute. In addition, it opens a new avenue for tuning stability in both nanoelectromechanical systems and microelectromechanical systems.