Double exchange bias and ultraslow magnetization relaxation in TbFe-based bilayers
Phys. Rev. B 113, 094401 – Published 2 March, 2026
DOI: https://doi.org/10.1103/bvp5-vpxn
Abstract
We report on the exchange coupling phenomena emerging at low temperatures in amorphous TbFe-based bilayers with perpendicular magnetic anisotropy. The ferrimagnetic layers have different compositions: one layer is dominated by the magnetic moment of Fe, the other by the magnetic moment of Tb. The antiferromagnetic exchange coupling between the two layers, along with the formation of an intermixing layer at the interface, leads to the emergence of (double) exchange bias [(D)EB] at low temperatures after field cooling. The composition of the Fe-dominated layer and the stacking order of layers are shown to have a significant impact on this behavior, while changes in the Tb-dominated layer and tailoring of the interlayer region influences it to a lesser degree. The most stable DEB was obtained in a bilayer structure, with clearly separated, oppositely biased subloops at temperatures up to 120 K. Further, a substantial overcrossing of hysteresis branches between 80 and 140 K was observed for some samples. This is shown to be connected to ultraslow magnetization dynamics similar to magnetic viscosity, which are greatly influenced by the applied magnetic field and temperature. Relaxation times ranging from tens of seconds to several hours are observed. By comparing minor loops with and without relaxation, a simple qualitative model is derived to explain the observed behavior of magnetization relaxation.
