NiCo₂O₄ constructed by different dimensions of building blocks with superior electromagnetic wave absorption performance

A series of NiCo₂O₄ absorbers constructed by different building cornerstones were successfully fabricated through precipitation-hydrothermal method. By adjusting the precipitants from NaHCO₃, urea, and NaOH to Na₂CO₃, the NiCo₂O₄ absorbers assembled through zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanorods and two-dimensional (2D) micro/nanoplates could be obtained. We found that NiCo₂O₄ absorbers formed by two-dimensional building blocks displayed high dielectric loss capacity but rather poor magnetic loss, resulting in inferior electromagnetic (EM) wave absorption performance. On the contrary, the sphere-like and urchin-like NiCo₂O₄ EM wave absorbing materials assembled by zero-dimensional nanoparticles and one-dimensional nanorods possess multiple magnetic loss mechanisms, which can achieve a balance with dielectric loss, leading to remarkably promoted EM wave attenuation performance. The effective absorption bandwidth for urchin-like and sphere-like NiCo₂O₄ is up to 5.84 GHz and 6.08 GHz at thickness of 1.88 mm and 2.06 mm, respectively. Moreover, the minimum reflection loss (RL_min) of sphere-like NiCo₂O₄ also reaches to −42.8 dB as well. The thin thickness, strong absorption capacity and wide effective absorption bandwidth (f_e), which is the widest among the previously reported NiCo₂O₄-based absorbers so far, is prone to be a competitive candidate as the materials for EM wave absorption devices.