Observations of rotating ferrofluid drop in a time-varying magnetic field

We report the stretch-shrink-rotation motion of a ferrofluid drop in a time-varying magnetic field along the x direction. The drop performs stretch and shrink motion at low magnetic field due to the balance of magnetic force and surface tension as observed in previous investigations, but it exhibits rotating motion at high magnetic field. The growth rate of rotating angle for the drop stretched to the maximum length is characterized. We find that the size of elongated drop shows transitions at Rayleigh frequency of drop and at the frequency with maximum growth rate. The phase diagram of growth rate to the frequency and the strength of applied magnetic field reveals the threshold for drop to rotate. It is suspected that the induced transverse magnetization for the magnetic torque is associated with the phase lag between the time-varying magnetic field and the deformation of drop which leads to the rotation of drop. Drop rotating along the y and z axis shows the evidence of transverse magnetization induced by the magnetic field in the x axis.

Automated summary

This study reports the stretch-shrink-rotation motion of a ferrofluid drop in a time-varying magnetic field along the x direction. The drop undergoes stretch and shrink motion at low magnetic field and rotating motion at high magnetic field. The growth rate of rotating angle for the stretched drop is characterized and the transitions of the size of the elongated drop are observed at specific frequencies. The phase diagram reveals the threshold for drop rotation and suggests the association of induced transverse magnetization with the phase lag between the magnetic field and drop deformation.