Al-Supermalloy and Al-Supermalloy@oxide magnetic powder. Structural, morphological, thermal, and magnetic characterization

A new alloy, Supermalloy alloyed with aluminum, in powder form, has been obtained by mechanical alloying using elemental powders. An amount of 5 wt% of Al has been added to Supermalloy (Ni75Fe20Mo5) resulting a magnetic alloy (Al-Supermalloy) with the nominal chemical composition of Ni71·25Fe19Mo4·75Al5 wt.%. The powder obtained after 20 h of mechanical alloying has been subjected to superficial oxidation to obtain Al-Supermalloy@oxide powder. The alloy is single FCC phase after 15 h of mechanical alloying having a mean crystallite size of 15 nm. In the early period of alloying the particles are flattened and irregular shaped, but by increasing the alloying time the amount of flattened particles decreases. At about 550 °C the recrystallisation of the structure is finished and further increase of the temperature leads to the increase of the crystallite size. The particles size of the single-phase alloy ranges from a few to tens of microns. The Curie temperature of the newly alloy is around 440 °C. The magnetization of the material increases even after the full formation of the single phase and several phenomena compete to this increase. The oxidation of the particles was successful resulting oxidized particles of Al-Supermalloy@oxide. The presence of oxides was proved by FTIR and EDX investigations. The magnetization of the core-shell composite is lowered only by 1.5% as compared to the uncovered sample this indicate that the oxide is present as a thin layer. The thickness of the oxide layer was estimated by magnetization measurement at about 100–200 nm.