Resolving the spin polarization and magnetic domain wall width of (Nd,Dy)$_{2}$Fe$_{14}$B with spin-polarized scanning tunneling microscopy

The electronic structure and the domain wall width of industrial (Nd,Dy)$_{2}$Fe$_{14}$B hard magnets were investigated using low-temperature, spin-polarized scanning tunneling microscopy (STM) in ultra-high vacuum. In a first step, atomically clean and flat surfaces were prepared. The flat terraces were separated by monatomic steps. Surface termination was identified as the Fe c layer from atomically resolved STM imaging. The electronic density of states and its spin polarization agree well with ab initio predictions of the Fe c layer. High-resolution spin-polarized STM images allowed to finally resolve the domain wall width w of only 3.2 ± 0.4 nm.