High-temperature magnetocaloric effect in devitrified Fe/Co based glassy monolayer and bilayer ribbons

Rapidly quenched Co- and Fe-based monolayer and their bilayer prepared through double nozzle technique have been characterized to investigate its microstructural and magnetic properties and their possibility as high-temperature magnetocaloric material. The Co- and Fe-based monolayer ribbons displayed Curie temperatures (T_C) of 463 K and 700 K, respectively. Magnetic entropy change ∆S_M of the bilayer was measured at a low magnetizing field of 1 T in the temperature spans covering separately for T_C of Co- and Fe-based ribbons corresponding to separate entropy at low- and high-temperature regime. The ∆S_M value at T_C of Fe-based ribbon displayed values in the span of 1.13–1.71 J kg⁻¹ K⁻¹ in their monolayer and bilayer state. On incipient nanocrystallisation at 773 K, the ∆S_M and refrigerant capacity (RC) around T_C of cobalt-based bilayer ribbon revealed comparable values as in their as-quenched state. However, nanocrystallisation elevated the ∆S_M of bilayer across T_C of the Fe-based regime to a high value close to 4.6 J kg⁻¹ K⁻¹ with a fairly elevated RC of 96 J kg⁻¹. The enhanced ∆S_M associated with the formation of Fe-based nanocrystallites is evidenced through transmission electron microscopy. The interdiffusion of ferromagnetic elements Fe and Co is also supposed to elevate the ∆S_M as well as the RC of the glassy system in the bilayer ribbons.