Effect of Co addition on magneto structural characteristics of Ni50_xCoxMn30Al20 Heusler alloys obtained by mechanical alloying process

Off-stoichiometric Ni-50_( x)Co(x)Mn(30)Al(20 )Heusler alloys were prepared by mechanical synthesis to study their structure, microstructure, morphology, chemical composition, and magnetic properties as a function of Co addition and at high temperature, using X-ray diffraction, SEM-EDS analysis, and VSM technique. At the end of the milling process, homogeneous mixtures consisting mainly of agglomerated grains of rounded shape with some debris of MICA-shaped particles were formed. All alloys have a nanocrystalline structure with an ordered Heusler B2 phase at 800 K. With increasing magnetization temperature, the crystallite size increases significantly by > 100%, however, the rate of microstrain decreases drastically due to the relaxation of residual stresses. High-temperature magnetic characterizations have shown that the addition of cobalt has a direct effect on the curie temperature of the alloys as well as on their magnetic parameters Hc, Mr, and Ms. As the percentage of Co decreases, the curie temperature drops until it reaches 300 K by replacing 5% of Ni with Co. Ni45Co5Mn30Al20 has the lowest curie temperature close to 300 K and exhibits a soft magnetic behavior characterized by high satu-ration magnetization (Ms), and low coercivity (Hc) with an interesting coupling-magnetic exchange, which makes it a suitable candidate for soft magnetic applications.