Microstructural dependence of magnetic and magnetostrictive properties in Fe-19 at% Ga

A combination study of magnetic and magnetostrictive properties in directionally cast (DC) (un-annealed) and differently heat-treated Fe-19 at% Ga samples was carried out at room temperature. Slow cooling leads to an increase in the occupation of [2 0 0] easy magnetic axis. However, structural ordering of Ga atoms into a metastable D0(3) phase decreases the saturation magnetostriction (lambda(s)) and saturation magnetization (M-s), while increases coercivity (H-c). Water quenching suppresses the formation of stable fcc ordered phase (L1(2)) and largely preserves disordered bcc single-phase (A2) structure down to room temperature, leading to enhanced magnetostriction and magnetization. Slow cooling promotes the ordering of metastable bcc ordered phase (D0(3)). Magnetic force microscopy (MFM) study exhibits that the water-quenched (WQ) sample consists of a well-aligned stripe domain structure, while irregular maze-like domain structure is observed in furnace-cooled (FC) sample. The results confirm that in addition to an inhibitory effect of D0(3) ordering on magnetic domain wall motions, irregular magnetic domains also contribute to decrease in magnetic and magnetostrictive properties of FC sample.