Negative imaginary parts of complex permeability and microwave absorption performance of core double-shelled FeCo/C/Fe_2.5Cr_0.5Se₄ nanocomposites

Abstract

Cactus-shaped core double-shelled FeCo/C/Fe2.5Cr0.5Se4 nanostructures with a spiky surface were prepared by combining an arc-discharge process with a high-temperature solution chemical method.

A Study on Microwave Absorption Properties of Carbon Black and Ni0.6Zn0.4Fe2O4 Nanocomposites by Tuning the Matching-Absorbing Layer Structures

“…6(a), the μ′ of carbon black as a matching layer and Ni 0.6 Zn 0.4 Fe 2 O 4 as an absorbing layer ranges from ~0.9 to 1.2 while μ″ varies from less than zero to 0.3. The negative μ″ values exhibited by the present samples has been observed in many composite systems previously by other workers, such as reduced graphene oxide and graphene oxide 40 , multi-walled carbon nanotube composite 41 , Fe 3 O 4 /SnO 2 core/shell nanorod 42 and FeCo/C/Fe 2.5 Cr 0.5 Se 4 nanocomposites 43 . This might be attributed to the phase lag between capacitance and inductance in the system as described in the equivalent circuit model proposed in 43 .…”

“…The negative μ″ values exhibited by the present samples has been observed in many composite systems previously by other workers, such as reduced graphene oxide and graphene oxide 40 , multi-walled carbon nanotube composite 41 , Fe 3 O 4 /SnO 2 core/shell nanorod 42 and FeCo/C/Fe 2.5 Cr 0.5 Se 4 nanocomposites 43 . This might be attributed to the phase lag between capacitance and inductance in the system as described in the equivalent circuit model proposed in 43 . It was observed that when carbon black acted as the matching layer and Ni 0.6 Zn 0.4 Fe 2 O 4 as the absorbing layer, only the samples with total thickness of 2 mm showed a broad hump from 11 to 18 GHz, somewhat indicating the occurrence of resonance loss, while resonances of thicker samples might have occurred at lower frequencies, as indicated by the decreasing trends of µ″ in the graph.…”

Polymer‐derived FexSiy/SiC@SiOC ceramic nanocomposites with tunable microwave absorption behavior

“…55 Equation ( 6) builds a relationship among permeability, conductivity (σ), wave frequency (f), and diameter of grains (D). 56 If the magnetic loss was predominantly caused by contributor (iii), the value of μ″(μ′) −2 f −1 should not change with the frequency variations. The peaks in Figure S3 indicate that contributor (iv) is the major cause for magnetic losses.…”

Broadband microwave absorber constructed by reduced graphene oxide/La0.7Sr0.3MnO3 composites

“…The phenomenon of the negative m 00 within the high frequency microwave range have been observed in many composite systems, such as hierarchical Ni nanostrucutres, multiwalled carbon nanotube composites, porous Fe 3 O 4 /SnO 2 core/shell nanorods, hollow cobalt nanochains, mesoporous carbon-silica nanocomposites, SiC nanowires, core doubleshelled FeCo/C/Fe 2.5 Cr 0.5 Se 4 nanocomposites and polymerderived SiCN ceramics. [31][32][33][34][35][36][37][38] Theoretically, in the case of diamagnetics (m 0 < 1), there is a strong indication that the negative imaginary part of the magnetic permeability does not contradict the second law of thermodynamics, nor any other conceivable physical constraints. 39 Typically, the permeability is very low due to the weak magnetic characteristic in the microwave band, so for rGO/LSMO composites, the decrease of 3 0 values and the increase of m 0 values benet the impedance matching, as shown in Fig.…”