The Surface and Bulk Magnetic Properties of Fe-Al Alloys

The present paper is devoted to Fe-Al alloys with aluminium content of 28, 33 and 35 at.%, prepared by standard technological procedure. The attention is focused on the comparison of the surface and bulk magnetic properties, which were obtained by magneto-optical Kerr effect (MOKE) and atomic and magnetic force microscopy (AFM/MFM) as the surface-sensitive methods combined with the vibration sample magnetometer (VSM) yielding the bulk magnetic properties. As was expected, the $Fe_{72}Al_{28}$ sample shows an overall ferromagnetic behavior at room temperature. Nevertheless, the bulk hysteresis loop shows single-phase behavior, while the surface MOKE hysteresis loop consists of two overlapped curves characterized by different coercivity values. The other two samples are paramagnetic from the viewpoint of the bulk, but reveal ferromagnetic behavior of their surfaces, represented by hysteresis loops, corresponding to rather harder magnetic phase. These results are well supported by MFM.