We report on the simplest magnetic nanowire-based surface walker that is able to change its propulsion mechanism near a surface boundary as a function of the applied rotating magnetic field frequency. The nanowires are made of CoPt alloy with semihard magnetic properties synthesized by means of template-assisted galvanostatic electrodeposition. The semihard magnetic behavior of the nanowires allows for programming their alignment with an applied magnetic field as they can retain their magnetization direction after premagnetizing them. By engineering the macroscopic magnetization, the nanowires' speed and locomotion mechanism are set to tumbling, precession, or rolling depending on the frequency of an applied rotating magnetic field. Also, we present a mathematical analysis that predicts the translational speed of the nanowire near the surface, showing a very good agreement with experimental results. Interestingly, the maximal speed is obtained at an optimal frequency (∼10 Hz), which is far below the theoretical step-out frequency (∼345 Hz). Finally, vortices are found by tracking polystyrene microbeads, trapped around the CoPt nanowire, when they are propelled by precession and rolling motion.

Departament de Física Universitat Autònoma de Barcelona E 08193 Bellaterra Spain

Faculty of Mechanical Engineering Technion Israel Institute of Technology 3200003 Haifa Israel

Institució Catalana de Recerca i Estudis Avançats Pg Lluís Companys 23 E 08010 Barcelona Spain

Institute of Physics Academy of Sciences of the Czech Republic Cukrovarnická 10 162 00 Praha 6 Czech Republic

Institute of Robotics and Intelligent Systems ETH Zurich CH 8092 Zurich Switzerland

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Magnetically Driven Micro and Nanorobots