Controllable synthesis, formation mechanism, and enhanced microwave absorption of dendritic AgFe alloy/Fe3O4 nanocomposites

Abstract

Single-crystalline dendritic AgFe alloy/Fe₃O₄ nanocomposites were successfully synthesized through galvanic replacement using Fe nanofibers as reducers and templates. The molar ratio of Ag⁺/Fe²⁺ (δ) and the aspect ratio of Fe nanofibers influence the compositions and sizes of the nanocomposites, respectively. The selective attachment at the {220} planes and anisotropic growth along the (111) plane affect the growth of dendritic nanocomposites. The composition-dependent static magnetic and microwave electromagnetic characteristics were studied systematically. Dendritic nanocomposites are typically ferromagnetic. The M_s decreases and H_c increases with increasing δ because of the increased content of antiferromagnetic Ag. Nanocomposites with δ = 1 : 1 and 2 : 1 exhibit significantly stronger absorption, thinner sample thickness, and lower bandwidth than pure Ag nanoparticles because of enhanced dielectric loss, magnetic loss, resonance absorption, and impedance matching. The bandwidth (R_L ≤ −10 dB) is 4.85 GHz, which corresponds to the minimum R_L value of −43.5 dB, and the absorption frequency range (R_L ≤ −20 dB) is 7.68 GHz. This work provides a general strategy for preparing dendritic Ag-based nanocomposites and a basis for further studies on using hierarchical heterostructures as microwave-absorbing materials.