Sharpening of core-shell microwire with four switchable magnetic states

Sharp ended α-Fe core microwire covered with PrDyFeCoB amorphous shell with enhanced stray magnetic field is proposed for magnetic tweezers, stepwise switchable in external homogeneous magnetic field. Four stable magnetic states of the microwire, controlled by external magnetic field, were determined by magneto-optical Kerr effect (MOKE) microscopy. Distribution of the stray field near the microwire tip was plotted by magneto-optical indicator film (MOIF) technique. Large gradient of the stray magnetic field in the vicinity of the microwire tip is quite enough to provide magnetic force ~ 2000 pN, well enough for capturing of the PrDyFeCoB microparticle. Significance of the obtained results is in switching of the focused stray field of the microwire under external homogeneous magnetic field. This provides simple way of stepwise attaching-detaching of microparticles without electromagnetic micro coils.