Strong microwave absorption observed in dielectric La1.5Sr0.5NiO4 nanoparticles

Abstract

La${}_{1.5}$Sr${}_{0.5}$NiO${}_4$ is well known to have a colossal dielectric constant (${\epsilon }_R>10^7$). The La${}_{1.5}$Sr${}_{0.5}$NiO${}_4$ nanoparticle powder was prepared by a combinational method of solid state reaction and high-energy ball milling. Magnetic measurements show that the material has a very small magnetic moment and paramagnetic characteristic at room temperature. The mixture of the nanoparticle powder (40% vol.) and paraffin (60% vol.) coated in the form of flat layers of different thicknesses ($t$) exhibits strong microwave absorption resonances in the 4-18 GHz range. The reflection loss ($RL$) decreases with $t$ and reaches down to -36.7 dB for $t=3.0$ mm. The impedance matching ($|Z|=Z_0=377$ $\Omega$), rather than the phase matching mechanism, is found responsible for the resonance observed in the samples with $1<t\le 3.0$ mm. Further increase of the thickness leads to $|Z|>Z_0$ at all frequencies and a reduced absorption. The influence of non-metal backing is also discussed. Our observation suggests that La${}_{1.5}$Sr${}_{0.5}$NiO${}_4$ nanoparticles could be used as good fillers for high performance radar absorbing material.