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Orientational bistability and field-controlled switching of a superparamagnetic dimer
James R N Tett1, Finlay Johnston1, Brennan Sprinkle2
1Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, UK. alice.thorneywork@chem.ox.ac.uk.
Soft Matter
|August 14, 2026
Summary
Superparamagnetic colloidal dimers exhibit unique orientational dynamics. Their magnetic response, featuring induced and permanent moments, dictates bistability and controlled rotations in changing magnetic fields.
Area of Science:
- Soft Matter Physics
- Colloidal Science
- Magnetism
Background:
- Superparamagnetic colloidal dimers possess both induced and permanent magnetic moments.
- Understanding their orientational dynamics is crucial for applications in micro-robotics and materials science.
- Previous studies often simplify the magnetic response, neglecting complex interactions.
Purpose of the Study:
- To investigate the orientational dynamics of superparamagnetic colloidal dimers under static and alternating magnetic fields.
- To elucidate the role of combined induced and permanent magnetic moments in dictating dimer behavior.
- To characterize the internal magnetic structure of these colloidal particles.
Main Methods:
- Experimental observation of superparamagnetic colloidal dimer dynamics using microscopy.
- Application of static and periodically reversed uniform magnetic fields.
- Analysis of orientational distributions, hopping events, and rotational dynamics.
Main Results:
- Dimers exhibit bistable orientational behavior in static fields, leading to a bimodal distribution.
- Periodic field reversal induces a sharp transition from small angle to full rotations (Δθ ≈ π).
- The observed dynamics are explained by a magnetic response comprising strong induced and weak permanent components.
Conclusions:
- The complex energy landscape, involving coupled roll-yaw rotations, underlies the observed bistability.
- The study successfully determines the net permanent dipole's magnitude and orientation.
- This work provides a method to characterize internal magnetic structures of colloidal particles.
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