Tailoring Magnetic Properties of FeCo Nanoparticles by Compositing with O ( = La, Nd, and Sm).

Fe-Co alloys are the most important soft magnetic materials, which are successfully used for a wide range of applications. In this work, the magnetic properties of lanthanide-substituted (FeCo)(O) ( = La, Nd, and Sm) nanoparticles, prepared by mechanical alloying, are reported. Our comprehensive studies (X-ray diffraction, Mössbauer spectroscopy, scanning electron microscopy with X-ray energy dispersive spectrometry, SQUID magnetometry and differential scanning calorimetry) have revealed different properties, depending on the dopant type. The O addition led to a decrease in the crystallite size and to an increase in the internal microstrain. Moreover, because of the high grain fragmentation tendency of O, the cold welding between Fe-Co ductile particles was minimized, indicating a significant decrease in the average particle size. The parent FeCo alloy is known for its soft ferromagnetism. For the La-substituted sample, the magnetic energy product was significantly lower (0.450 MG·Oe) than for the parent alloy (0.608 MG·Oe), and much higher for the Sm-substituted compound (0.710 MG·Oe). The processing route presented here, seems to be cost-effective for the large-scale production of soft magnetic materials.