Magnetic and microwave absorbing properties of La0.7Sr0.3MnO3 nanoparticles

Abstract

The magnetic and absorbing properties of La0.7Sr0.3MnO3 nanoparticles created by ceramic and high-energy ball milling methods were investigated in detail in this study. The x-ray diffraction data show that they belong to a rhombohedral structure with an average crystalline size of ⟨ D⟩ = 41 ± 2 nm. The field emission scanning electron microscope image showed that the La0.7Sr0.3MnO3 particles have a pseudo-spherical shape with particle sizes ranging from 20 to 100 nm. The Curie temperature ( TC), effective paramagnetic moment, coercivity ( Hc), and saturation magnetization ( Ms) of the sample were determined using the temperature and magnetic field dependences of the magnetization. It shows that La0.7Sr0.3MnO3 nanoparticles exhibit a soft ferromagnetism with TC = 358 K and Hc ≈ 15 Oe and Ms ≈ 60 emu/g at 300 K. The microwave reflection loss ( RL) of La0.7Sr0.3MnO3–paraffin composites with thicknesses t = 1.5–3.5 mm at room temperature was measured at frequencies 4–18 GHz using a vector network analyzer. The largest negative RL values obtained for un-backed and Al-backed samples are about −14.07 dB at 17.97 GHz and −24.87 dB at 14.71 GHz corresponding to the absorbing thicknesses t = 1.5 and 2.0 mm, respectively. These resonant effects are explained by the impedance matching mechanism in the samples.