Negative imaginary parts of complex permeability and microwave absorption performance of core double-shelled FeCo/C/Fe2.5Cr0.5Se4 nanocomposites

Abstract

Cactus-shaped core double-shelled FeCo/C/Fe_2.5Cr_0.5Se₄ nanostructures with a spiky surface were prepared by combining an arc-discharge process with a high-temperature solution chemical method, in which FeCo nanoparticles serve as the, while carbon and ferrimagnetic Fe_2.5Cr_0.5Se₄ (FCS) are the inside and the outside shells, respectively. The magnetic properties, electromagnetic response, and microwave absorption properties of the (x)FeCo/C/FCS nanocomposites in the 1–18 GHz frequency range were investigated by changing the mass ratio x between FeCo/C and FCS. The frequency dependences of μ′′ (imaginary parts of complex permeability) and ε′′ (imaginary parts of complex permittivity) of the (0 ≤ x ≤ 0.15)FeCo/C/FCS nanocomposites show distinct inverse trends of change in the high frequency ranges. Negative minimum values of μ′′ are found to be coupled with positive maxima of ε′′ due to a phase lag. The bare FCS–paraffin composite starts with a minimum μ′′ of about −0.07, which shifts to −0.44 and −0.05 when the mass ratio x is increased to 0.1 and 0.15, respectively. As x increases to 0.2, all the μ′′ values of the nanocomposites become positive. The best absorption property with a reflection loss (RL) peak of −54.5 dB at 10 GHz is obtained in the (x = 0.1)FeCo/C/FCS–paraffin composite and RL exceeding −20 dB can be achieved within the 3–18 GHz frequency range by choosing an appropriate layer thickness between 1.4 and 6 mm. The contribution of the negative μ′′ response to the microwave absorption is discussed.