Cryogenic Focused Ion Beam Milling to Investigate the Anisotropic Magnetotransport Properties of Bismuth Microcrystals

Abstract Bulk single crystals exhibit the intrinsic properties of a given compound, but studying their anisotropic magnetotransport properties is challenging. Focused Ion Beam (FIB) milling at room temperature has been previously used to guide the electrical current path along a defined crystal direction or to extract microcrystals where the electrical current flows along a known direction. However, some materials, such as bismuth, melt under FIB irradiation. Bismuth, known for its unique properties, including very large magnetoresistance and a highly anisotropic Fermi surface, reacts to room‐temperature Ga + FIB irradiation, forming droplets on its surface. Therefore, a novel microfabrication approach based on cryogenic FIB milling is developed here. By using a Peltier stage or an integrated cryogenic module, surface melting is mitigated below −30 °C. Microscale slabs are extracted, either parallel or perpendicular to the single crystal surface, then shaped and electrically contacted in a chip for magnetotransport characterization. The large magnetoresistance observed along with Shubnikov–de Haas oscillations with single periodicity when current is applied perpendicular to the c axis, highlights the success of the approach. These results enable FIB microfabrication of single crystals that are sensitive to FIB irradiation and investigation of the anisotropic magnetotransport properties in microcrystals.