Electrical detection of magnetic domain wall in Fe4N nanostrip by negative anisotropic magnetoresistance effect

The magnetic structure of the domain wall (DW) of a 30-nm-thick Fe4N epitaxial film with a negative spin polarization of the electrical conductivity is observed by magnetic force microscopy and is well explained by micromagnetic simulation. The Fe4N film is grown by molecular beam epitaxy on a SrTiO3(001) substrate and processed into arc-shaped ferromagnetic nanostrips 0.3 μm wide by electron beam lithography and reactive ion etching with Cl2 and BCl3 plasma. Two electrodes mounted approximately 12 μm apart on the nanostrip register an electrical resistance at 8 K. By changing the direction of an external magnetic field (0.2 T), the presence or absence of a DW positioned in the nanostrip between the two electrodes can be controlled. The resistance is increased by approximately 0.5 Ω when the DW is located between the electrodes, which signifies the negative anisotropic magnetoresistance effect of Fe4N. The electrical detection of the resistance change is an important step toward the electrical detection of current-induced DW motion in Fe4N

Nanoscale measurement of giant saturation magnetization in α″-Fe16N2 by electron energy-loss magnetic chiral dichroism

Metastable α″-Fe16N2 thin films were reported to have a giant saturation magnetization of above 2200 emu/cm3 in 1972 and have been considered as candidates for next-generation rare-earth-free permanent magnetic materials. However, their magnetic properties have not been confirmed unequivocally. As a result of the limited spatial resolution of most magnetic characterization techniques, it is challenging to measure the saturation magnetization of the α″-Fe16N2 phase, as it is often mixed with the parent α′-Fe8N phase in thin films. Here, we use electron energy-loss magnetic chiral dichroism (EMCD), aberration-corrected transmission electron microscopy, X-ray diffraction and macroscopic magnetic measurements to study α″-Fe16N2 (containing ordered N atoms) and α′-Fe8N (containing disordered N atoms). The ratio of saturation magnetization in α″-Fe16N2 to that in α′-Fe8N is determined to be 1.31 ± 0.10 from quantitative EMCD measurements and dynamical diffraction calculations, confirming the giant saturation magnetization of α″-Fe16N2. Crystallographic information is also obtained about the two phases, which are mixed on the nanoscale