R1l3s2p

The microelectode cell was illuminated in transmitted light configuration using an light-emitting diode light source (MCWHLP1, Thorlabs), a collimator (COP4-A, Thorlabs), and a diffuser. Imaging was done with a 10× finite-conjugate objective lens (Nikon 10×/0.25 160/−WD5.6) or a 4× finite-conjugate objective lens (Nikon 4×/0.25 160/−WD25) connected to a five-megapixel gray scale camera (MC050MG-SY, Ximea). Image length scale was calibrated using a calibration target (R1L3S2P, Thorlabs). Images were acquired using software provided by the camera manufacturer (xiCamTool 4.28, Ximea). In most experiments, images were acquired at 100 frames per second (fps) with averaging of five consecutive frames to reduce noise, resulting in final acquisition rate of 20 fps. The Rosensweig-like instabilities (Fig. 4, B and C) were imaged at 5 fps with averaging five consecutive images, leading to 1 fps, and the control experiments in polar solvent (fig. S3) at 30 fps with no image averaging. Images used for the voltage-controlled magnetism analysis (Fig. 2G) were acquired after 20 s stabilization at each voltage without averaging.

A block-matching program was implemented in MATLAB to obtain micropillar deflection by recording the time series of the selected ROI within the specified measurement period. Before tracking started, the centers of the correlation window were manually selected on a snapshot (reference frame for the correlation) of the entire wellplate. Typically, features with high contrast such as the notches on the cap of the µTUGs were selected to maximize imaging quality. 96 correlation windows were generated with width and height set for the configured optical setting (overall magnification of the optics). MATLAB then continuously tracks the target feature in each correlation window. Parallel computing must be enabled to allow larger processing bandwidth than video acquisition. Length of each measurement video was controlled at 2000 frames (∼30 s). Deflection of the micropillar was obtained by averaging the peaks on the selected segments of the displacement-time plot. To convert the imaged deflection in pixels to microns, an optical ruler (R1L3S2P, Thorlabs) with precise line gratings of known lengths was imaged.