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.