Chemical Design of DyPrFeCoB-Alloy-Based Microtweezers

Using selective dissolution, we create α-Fe/DyPrFeCoB microwires with a parabolic tip for focusing the magnetic flux and enhancing the magnetic attraction of particles. The conditions for sharpening the end of the microwire by etching with HNO 3 and with mixtures of HNO 3 + HCl and H 2 SO 4 + HNO 3 are also optimized. The magnetic force of a single microwire with a pointed end (up to 880 pN) makes it possible to capture and hold a DyPrFeCoB microparticle with a size of 1 µm in the region of ~5 µm. A significant magnetic-field gradient (up to ~3.5 × 10 5 T/m), created at the tip of the microwire, is sufficient to affect biological processes inside cells even without magnetic markers. The conditions for the attachment/detachment of a magnetic microparticle are controlled by the exchange bias arising at the interface between the α-Fe ferromagnetic core and the PrDyFeCoB ferrimagnetic shell and by four magnetic states of the microwire, which are switched by a weak external uniform magnetic field of ~0.1–2 kA/m.