Size effects on the magnetic characteristics of a nanostructured Heusler alloy

Abstract

A systematic study of the size effect on the structural and magnetic properties of Co2FeAl ternary alloys with different particle sizes has been performed in this work. The average particle size was controlled in a range from a few nanometers to micrometers by tuning the annealing rate. Upon annealing process at 700 C in the presence of the surfactant matrix of CTAB, the B2-ordered structures with an average particle size of 35 nm were obtained under heating rate of 15 C/min. Decreasing the reaction rate provided a well-arranged crystallization, leading to an enhanced saturation magnetization as well. For studying the effect of surfactant, samples were also synthesized in the absence of CTAB. A higher agglomeration is clearly observed in these samples compared to the previous ones, and the particle size was found to be significantly affected by the presence of surfactant, in spite of the magnetization. First-order reversal curve analysis revealed the presence of low- and high-coercive field particles in both samples, indicating that the products were composed of an assembly of particles with different sizes. By isolating the reversible and irreversible components of the magnetization, it was found that the behavior of the prepared samples is reversible (more than 59 %) as the percentage of the reversibility increased with decreasing the average particle size.