Fig shows the calculated RL

The morphologies of as-prepared Ni/C nanocomposites were examined with a field emission scanning PF00562271 microscope (FESEM, JEOL JSM-5600LV, accelerating voltage 20 kV). A Philips X’Pert Pro X-ray diffractometer (XRD, Philips Corporation, the Germany) was performed to analyze the phase structure of as-synthesized Ni/C nanocomposites (Cu Kα radiation, λ = 1.5406 Å). Raman scattering spectra were measured with a confocal microscopic Raman spectrometer (RM-1000, Renishaw, England) using a 632.8 nm laser as the excitation source. Magnetic measurements were conducted with a nervous system vibrating sample magnetometer (VSM, Lake Shore 7400, America). Moreover, a proper amount of as-synthesized Ni/C nanocomposite was homogeneously dispersed in paraffin at a mass ratio of 1:1 and then pressed into a toroidally-shaped sample (inner diameter 3.04 mm, outer diameter 7.00 mm) for measurements of electromagnetic properties [20]. The electromagnetic properties of resultant Ni/C-paraffin composites were measured in a frequency range of 2.0–18.0 GHz with an Agilent N5230A vector network analyzer (Agilent, America).