Giant exchange bias in the nanostructured MnAl thin ribbons

Abstract

In this study, Mn54Al46 thin ribbons composed of nanostructured ferromagnetic and antiferromagnetic phases were fabricated by a melt spinning method, and a tunable exchange bias field was obtained by precisely controlling the wheel speed and the cooling field. The x-ray diffraction result confirms the existence of the nanostructured Mn-poor ε phase. The pinned ferromagnetic Mn-poor ε phase coupled with the antiferromagnetic Mn-rich ε phase accounts for the exchange bias observed in the sample fabricated at a wheel speed of 65 m/s in which almost no τ phase is formed. Furthermore, the exchange bias field first increases and reaches the most significant reported value of 41 kOe in this system and then decreases with the increase in the cooling field, exhibiting an inversely proportional relationship with the magnetization. The decrease in the exchange bias field is believed to be related to the increased coupling thickness of the ferromagnetic phases with the increase in the cooling field.