New Publication: Controlling collective rotational patterns of magnetic rotors

Josh Hamilton

Congratulations to CDT alumnus Dr.Joshua Hamilton,  whose paper Controlling collective rotational patterns of magnetic rotors has recently been published in Nature Communications. Josh works as a postdoctoral research fellow in TEAM-A  at University of Exeter.

A summary of the paper is below:

Combining experiments, simulations, and theoretical arguments Josh Hamilton and his collaborator Daiki Matsunaga have investigated the collective motion of arrays of magnetic rotors. The surprising complex dynamics was shown to generate a fluid flow at a low Reynolds number. There creating a possibility for a method of mixing and/or pumping fluids on the micrometre scale. Depending on the combinations of the relative strengths of the external magnetic field and the dipolar interactions between the rotors, a range of collective motions was achieved. Two examples of the collective motions shown were known as the “stripe-swinging” and the “quarter-rotational” patterns.

In its simplest form, the stripe-swinging pattern occurs when the dipolar interaction between the rotors dominates over the external magnetic field. The dynamics can be understood by regarding the pattern as adding small perturbation to the rotors base condition. In their resting position, the rotors create a two-in, two-out pattern (known as a spin-ice structure). The two-in, two-out pattern intrinsically has the characteristics of a stripe. Therefore, if a small external magnetic field were applied, the rotors would form a stripe pattern and swing together back-and-forth.

The quarter-rotational pattern occurs when the interaction between the external magnetic field and the rotors is stronger than the dipolar interaction. In this mode, the rotors undergo full rotations with different quadrants of the arrays of the array turning in different directions, either clockwise or counter-clockwise. The collective rotation of the rotors was shown to be used to mix or pump fluid.

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