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Excellent NiO-Ni Nanoplate Microwave Absorber via Pinning Effect of Antiferromagnetic-Ferromagnetic Interface Wenbin You, and Renchao Che ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03610 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 13, 2018
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ACS Applied Materials & Interfaces
Excellent NiO--Ni Nanoplate Microwave Absorber via Pinning Effect of Antiferromagnetic-Ferromagnetic Interface Wenbin You and Renchao Che* Laboratory of Advanced Materials, Department of Materials Science, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fudan University, 220 Handan Road, Shanghai 200433, China * E-mail:
[email protected] Abstract Materials with strong magnetic property that can provide excellent microwave absorption performance are highly desirable, especially if their dielectric and magnetic properties can be easily modulated, which make minimal thickness and ultra-wide bandwidth become achievable. The magnetic property of ferromagnetic (FM) and antiferromagnetic (AFM) composite materials are closely related to their ratio of composition, size, morphology and structure. AFM-FM composites become a popular alternative for microwave absorption, however, the controllable design and preparation need urgently optimized. Here, we have successfully prepared a series of plate-like NiO-Ni composites and demonstrated the potential of such composites for microwave absorption. Strong magnetic coupling was found from NiO-Ni nanoparticles by electron holography, which makes NiO-Ni composite a highly efficient microwave absorber (strong reflection loss: -61.5 dB and broad bandwidth: 11.2 GHz, RL < -10 dB). Our findings are helpful to develop strong microwave absorber based on magnetic coupling.
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Keywords: microwave absorption, AFM-FM composite, plate-like, magnetic coupling, electron holography 1. Introduction The electromagnetic pollution problem has even become worse due to the popularity of telecommunications equipment, digital systems and electronic devices.1-2 The microwave absorption materials directly converts electromagnetic (EM) wave energy into thermal energy or dissipates EM wave via interference.3-4 Magnetic metal-based absorber have been attracting intense attention because of the high efficiency and easy convenience.5
An effective absorber must both sufficiently reduce microwave reflection and effectively work in different antidetection waveband.6-7 The primary target of absorber design is the impedance matching that make microwave penetrate into material without surface reflection.8 The classical method is to combine special ratio of dielectric materials (e.g., SiO2,8 TiO2,9 Carbon10) and magnetic materials (e.g., Fe3O4,11 Ni,12 Co13) via core-shell structure, multi-layers design and carrier loading. The secondary important point of structure design is to provide internal scattering14 via void15 or interface16 for microwave energy dissipation. However, the equally important modulation to the intrinsic dielectric and magnetic properties of absorbing material itself is less studied, which can actually adjust the microwave absorption performance.17 Especially, to achieve strong absorption performance via magnetism modification still remains a great challenge. In essence, the material magnetization comes mainly from the movement or
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ACS Applied Materials & Interfaces
displacement from electric charge. Previously, tuning magnetic property of absorber could be realized by optimizing the synthesis parameters to fabricate materials with special morphology and suitable grain size.18-19 Control magnetic core size is another way to tuning magnetic property of absorber with core-shell structure. However, the above routines are usually too complicated to facilely produce lightweight, low-cost absorbers.2, 15 Remarkably, the transition metals conjugated with their oxides used as ferromagnetic (FM) and antiferromagnetic (AFM) materials have become a popular alternative for microwave absorption.20-21 Because the magnetic property of AFM-FM composites can be easily controlled by tuning the composition ratio, size, morphology and structure.22-23 Besides, there are many interesting phenomena exhibiting in the heterojunction interface of AFM-FM, such as the exchange bias effect and giant magnetoresistance effect, which finally exhibit unexpected magnetism behavior in material23-24 and may benefit microwave absorption. The usual procedures followed to obtain AFM/FM nanocomposite absorbers are creating oxide shell out of FM nanoparticles (e.g., Fe, Co and Ni) by different techniques,25-28 such as thermal decomposition and chemical reduction. Among all transition metal, nickel29 has attracted extensive interests because its oxide (NiO) shows a high Néel temperature (523 K of bulk materials) which makes it AFM under room temperature.30 Besides, compared to the nanoparticles of Fe31 and Co32 in air, the Ni nanoparticles are more stability and less likely to be oxidized spontaneously. In addition, the Ni-NiO nanocomposites can exhibit high Hc value due to the existing of NiO,33 which can offset the paramagnetism of Ni nanoparticle and ensure the
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potential magnetic loss.23 At the same time, NiO works not only as an AFM material but also as a dielectric material which ensures the impedance matching with Ni.20 However, conventional synthesis methods of Ni-NiO composites usually obtain an uncertain quantity of NiO and nouniformity between different particles.34 The unstable magnetic property of previous Ni-NiO composite makes it difficult to be used for microwave absorption. As far as we know, the absorption mechanism of Ni-NiO composite absorber have been rarely reported. Herein，we report a facile and controllable process for the fabrication of Ni-NiO nanocomposites, which exhibit an excellent microwave absorption performance. The Ni-NiO heterojunction was obtained onside the surface of NiO nanoplate by the reduction of Ni(OH)2@polydopamine. The content of Ni was controlled by tuning the polymer layer thickness of Ni(OH)2@polydopamine precursor. The electromagnetic parameters display the influence of magnetic microstructure and the content of Ni (FM) on the magnetic properties of AFM-FM system by our electron holography analysis. Our Ni-NiO nanocomposites have additional advantages such as easy processing, strong reflection loss (-61.5 dB, coating thickness =3.24 mm at 6.5 GHz) and broad bandwidth (11.2 GHz, RL
