Exchange coupling and microwave absorption in core/shell structured hard/soft ferrite based CoFe2O4/NiFe2O4 nanocapsules Exchange coupling and microwave absorption in core/shell structured hard/soft f[.]
Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2O4/NiFe2O4 nanocapsules Chao Feng, Xianguo Liu, Siu Wing Or, and S L Ho Citation: AIP Advances 7, 056403 (2017); doi: 10.1063/1.4972805 View online: http://dx.doi.org/10.1063/1.4972805 View Table of Contents: http://aip.scitation.org/toc/adv/7/5 Published by the American Institute of Physics Articles you may be interested in Self-biased microwave ferromagnetic performance of patterned Ni80Fe20 thin films AIP Advances 7, 056301056301 (2016); 10.1063/1.4972799 Observation of large magnetocaloric effect in equiatomic binary compound ErZn AIP Advances 7, 056401056401 (2016); 10.1063/1.4972796 Effect of disorder on the magnetic and electronic structure of a prospective spin-gapless semiconductor MnCrVAl AIP Advances 7, 056402056402 (2016); 10.1063/1.4972797 Exchange bias effect in CaMn𝟏-𝒙Re𝒙O3 AIP Advances 7, 055801055801 (2016); 10.1063/1.4972798 AIP ADVANCES 7, 056403 (2017) Exchange coupling and microwave absorption in core/shell-structured hard/soft ferrite-based CoFe2 O4 /NiFe2 O4 nanocapsules Chao Feng, Xianguo Liu, Siu Wing Or,a and S L Ho Hong Kong Branch of National Rail Transit Electrification and Automation Engineering Technology Research Center, Hong Kong and Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (Presented November 2016; received 23 September 2016; accepted October 2016; published online 20 December 2016) Core/shell-structured, hard/soft spinel-ferrite-based CoFe2 O4 /NiFe2 O4 (CFO/NFO) nanocapsules with an average diameter of 17 nm are synthesized by a facile two-step hydrothermal process using CFO cores of ∼15 nm diameter as the hard magnetic phase and NFO shells of ∼1 nm thickness as the soft magnetic phase The singlephase-like hysteresis loop with a high remnant-to-saturation magnetization ratio of 0.7, together with a small grain size of ∼16 nm, confirms the existence of exchangecoupling interaction between the CFO cores and the NFO shells The effect of hard/soft exchange coupling on the microwave absorption properties is studied Comparing to CFO and NFO nanoparticles, the finite-size NFO shells and the core/shell structure enable a significant reduction in electric resistivity and an enhancement in dipole and interfacial polarizations in the CFO/NFO nanocapsules, resulting in an obvious increase in dielectric permittivity and loss in the whole S–Ku bands of microwaves of 2–18 GHz, respectively The exchange-coupling interaction empowers a more favorable response of magnetic moment to microwaves, leading to enhanced exchange resonances in magnetic permeability and loss above 10 GHz As a result, strong absorption, as characterized by a large reflection loss (RL) of -20.1 dB at 9.7 GHz for an absorber thickness of 4.5 mm as well as a broad effective absorption bandwidth (for RL