Annealing-induced softening and metamagnetictransition control in MnFePSi microwires

Abstract

The effect of high-temperature annealing on the magnetic, morphological, and microstructural properties of MnFePSi glass-coated microwires (GCMWs) and bulk sample is studied. A comparative analysis is conducted to elucidate the direct influence of annealing at 1373 K on their physical characteristics. Notably, significant differences in magneto-structural behavior are observed between as-prepared GCMWs and the bulk alloy. For the bulk sample, annealing promotes homogenization and a decrease in the average grain size from 24 μm to 2 μm, as confirmed by SEM and XRD analyses. In contrast, a broader grain size distribution in MnFePSi GCMWs, ranging from 0.8 μm to 40 nm compared to the as-prepared sample's with relatively uniform size of 36 nm is induced by annealing. Additionally, annealing enhances the Fe₂P phase content in both samples. The annealing process significantly affects magnetic properties of MnFePSi GCMWs. A notable reduction in coercivity (H_c) is observed, with a decrease in H_c from 761 Oe (as-prepared) to H_c = 46 Oe (annealed), as evaluated from the hysteresis (M − H) loop measured at T = 5 K. The as-prepared MnFePSi-GCMWs exhibit a unique metamagnetic phase transition in M − H loops measured at various temperatures (200 K–5 K). Conversely, the annealed GCMWs display a more uniform metamagnetic transition in M − H loops measured at T = 20 K and 5 K. Furthermore, as-prepared GCMWs exhibit multistep magnetic M − H loops below 100 K, which is absent in the annealed samples. This study underlines the substantial effect of the annealing on MnFePSi-GCMWs, enabling the tailoring of magnetic phenomena, such as metamagnetic phase transition, multistep magnetic behavior, and the control of magnetic response (hardening/softening). These tailored properties can be exploited in a wide range of applications based on glass-coated microwires.