Magnetic Properties and Exchange Coupling Effects of SrFe12O19@MFe2O4 (M = Co, Ni, Zn) as Hard-Soft Magnetic Ferrite Core–Shell Nanofibers

In this study, SrFe 12 O 19 @MFe 2 O 4 (M = Co, Ni, Zn) core–shell nanofibers were fabricated by coaxial electrostatic spinning. The composites obtained at an annealing temperature of 900 °C are composed of SrFe 12 O 19 in pure phase and MFe 2 O 4 (M = Co, Ni, Zn) in different spinels. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscope (TEM) were used to describe the structure and morphology of nanofibers. Magnetic Property Measurement Systems (MPMS) are used to characterize the magnetic properties of nanofibers. Sr@Ni and Sr@Zn fibers all exhibit a unique core–shell structure, while Sr@Co fibers are connected by a lamellar structure. The single-phase hysteresis lines for each composite indicate the presence of exchange coupling effects between the hard/soft magnetic composite phases. The magnetic properties of the composites change as the soft magnetic material in the shell layer changes. Sr@Co has the highest M s (69.43 emu/g) and M r (33.82 emu/g), whereas Sr@Zn has the highest H c (2927 Oe). The switching plant curves indicate that the best exchange coupling of the three groups of samples is for Sr@Co. The magnetic properties of the composites are explained in terms of the nanofiber diameter, the exchange coupling between the two phases, and the nature of the soft magnetic phase itself. It is shown that the exchange coupling of composites is closely related to the type of composite.