Microstructures and Corresponding Magnetic Properties of BaAl Fe O Nanopowders

We present the results of the magnetic domain structures of BaAl 2 Fe 10 O 19 nanopowders prepared by a self-propagating combustion process. Amorphous precursors were calcined at 850 °C for 2 h with NaCl (Sample I) and without NaCl (Sample II). The transmission electron microscope and atomic force microscopy images evidently suggested that there was a topological difference between Sample I (plate- and rod-shaped nanopowders) and Sample II (rod-shaped nanoparticles). We observed a considerably enhanced coercivity in Sample II, compared to Sample I. This result can be understood by the change in the magnetic domain width due to the shape effect of the nanopowders, which was investigated by measuring the field-controlled magnetic force microscopy.