Exchange bias behaviour of amorphous CoFeNiSiB ribbons

A dramatic exchange bias behaviour was found in superior soft Co ₅₈Fe₅Ni₁₀Si₁₁B₁₆ amorphous ribbons with proper thermomagnetic annealing conditions. This characteristic, which was directly obtained at room temperature, is quite different from that of the traditional ferromagnetic-antiferromagnetic system. The observation of microstructure indicated that the matrix of the annealed ribbons with the exchange bias behaviour includes a few crystalline phases. The magnetic domains of the ribbon surface were scanned to clarify the configuration of local magnetic moments. A subsequent magnetic torque measurement revealed that unidirectional magnetic anisotropy was induced in the amorphous ribbons with a longitudinal field. The obtained evidence supports our point of view that the local crystalline phases in the ribbons along with the longitudinal thermomagnetic treatment are the key factors in promoting the formation of an exchange bias. A simple phenomenological discussion was developed to expound this interesting behaviour in ribbons.