Exchange bias material: FeMn

Abstract

Since the exchange bias (EB) effect was discovered in the Co/CoO core-shell nanoparticles, it has been extensively studied in various ferromagnet/antiferromagnet material systems, both in experiments and in theory. Among many antiferromagnetic materials, metastable ?-FeMn emerges as the ideal material to reveal the physics mechanism behind the EB. In this chapter, the EB properties of FeMn-based bilayers are introduced by starting with the analysis of the spin configuration and structural and physical properties of bulk ?-FeMn, followed by the discussion of some basic features of the ferromagnetic/FeMn bilayers, such as the exchange field, the coercivity, the rotational hysteresis loss, and the blocking temperature as a function of the FeMn layer thickness, its crystalline microstructure, and temperature. Additionally, the thermal stability and training effect of the EB, the hysteretic effect of the angular dependent EB, and in particular the rotation of the pinning direction will be discussed in detail. The crucial role of the irreversible motion of FeMn spins will be analyzed as well.