Magnetic properties and spin dynamics of CoFeB–SiO2 multilayer granular heterostructures

Abstract

It has been found that CoFeB–SiO₂/C and CoFeB–SiO₂/Bi₂Te₃ multilayer heterostructures with a cluster structure of CoFeB layers feature a long-range magnetic order in the entire temperature range from 2 to 300 K. At high temperatures (T = 300 K), CoFeB clusters exhibit magnetic properties characteristic of superparamagnets. At low temperatures (T = 5 K), clusters are ferromagnetic, and the easy magnetization axis is in the film plane. The temperature of the ferromagnetic-to-superparamagnetic state transition of clusters depends on a dielectric interlayer material: the use of Bi₂Te₃ instead of C as a spacer layer leads to an increase in the transition temperature by a factor of 4 and an increase in the magnetization blocking temperature of CoFeB clusters in a field of 100 Oe by a factor of 3.