Bismuth ferrite (BiFeO3) nanoparticles has been synthesized by coprecipitation method with various NaOH concentration (4, 6, 8, and 10 M) and temperature (RT, 60, 80, and 100 C). X-ray diffraction patterns showed the emergence of Bi(OH)3 and Bi25FeO40 structures with crystallite size in the range of 15.1 nm to 35.6 nm. The particles sample was agglomerated. Hysterisis loop showed the linear M–H loops behaviour with no magnetization saturation in 15 kOe maximum field applied which indicates the antiferromagnetic properties. The coercivity field tends to increase by the increasing of the NaOH concentration and synthesis temperature. In addition, the annealing treatment could leads the increasing of coercivity fields while decreasing the magnetization of BFO sampel.

The design of audio bio harmonic (ABH) with smart-chip WT5001 using solar cell technology in the form of ABH instrumentation with an electricity resource derived from solar energy has been successfully created and tested, which includes (i) testing the peak frequency of sound and sound output, and (ii) emptying and charging tests to determine the effectiveness of the use of the solar cell as the power provider. The ABH system consists of (i) a sound generator device composed of WT5001 sound modules, amplifiers, and horn speakers, and (ii) structured power supply devices for solar cell modules, charge controllers, and batteries for storing power. The test results of the peak frequency for the insect (garengpung) sound files and the output sound of the ABH device indicate a deviation of the peak frequency of 13.46 Hz to 140.81 Hz. The 15 hours emptying test results in on mode with battery charging for 7 hours shows that the use of 10Wp solar cell is effective to provide electrical power in ABH tool operation.

In this study, the microstructural, optical, and magnetic properties and specific absorption rate (SAR) of bismuth ferrite/SiO2 nanoparticles were successfully investigated. The coprecipitation method was used to synthesize the nanoparticles. X-ray diffraction patterns showed the presence of sillenite-type Bi25FeO40 with a body-centered cubic structure. The crystallite size of Bi25FeO40 was 35.0 nm, which increased to 41.5 nm after SiO2 encapsulation. Transmission electron microscopy images confirmed that all samples were polycrystalline. The presence of Si–O–Si (siloxane) stretching at 1089 cm−1 in Fourier transform infrared spectra confirmed the encapsulation of SiO2. Magnetic measurements at room temperature indicated weak ferromagnetic properties of the samples. The coercivity of the bismuth ferrite nanoparticles was 78 Oe, which increased after SiO2 encapsulation. In contrast, their maximum magnetization, 0.54 emu g−1, reduced after SiO2 encapsulation. The determined bandgap energy of the bismuth ferrite nanoparticles was approximately 2.1 eV, which increased to 2.7 eV after SiO2 encapsulation. The effect of SiO2 encapsulation on the SAR of the samples was investigated using a calorimetric method. The SAR values of the bismuth ferrite nanoparticles were 49, 61, and 84 mW g−1 under alternating magnetic field (AMF) strengths of 150, 200, and 250 Oe, respectively, which decreased after SiO2 encapsulation. The maximum magnetization and the AMF strength influenced the SAR of the nanoparticles. The results showed that SiO2 has a significant effect in determining the microstructural, optical, and magnetic properties and SAR of the nanoparticles.

Bismuth ferrite nanoparticles were successfully synthesized by the co-precipitation method and modified by polyethylene glycol (PEG) 4000. X-ray diffraction patterns showed a sillenite structure of bismuth ferrite (Bi25FeO40) with a crystallite size of 35.0 nm and the new phase appeared after surface modification. The new phase was Bi2Fe4O9. Crystallite size increased after surface modification of nanoparticles with PEG. The highest increase of crystallite size after surface modification with PEG was 40.1 nm. Transmission electron microscopy images showed that samples before and after surface modification were polycrystalline and still agglomerated. Spectra of Fourier transform infrared showed the presence of C-O stretching at 1080 cm-1 and C-H bending vibration at 1342 cm-1 in the bismuth ferrite/PEG sample, which did not appear in bismuth ferrite sample. The magnetic measurement indicated the weak ferromagnetic properties of the samples. Saturation magnetization did not appear after a maximum external magnetic field (15 kOe) was applied. The maximum magnetization of nanoparticles was 0.5 emu/g and tended to decrease to 0.2 emu/g after surface modification with PEG. Optical properties analysis showed a shift in the maximum absorption peak of bismuth ferrite nanoparticles towards a lower wavelength (blue shift) after surface modification of the nanoparticles. The specific absorption rate (SAR) value of nanoparticles increased by increasing an alternating magnetic field (AMF) strength. The SAR values of bismuth ferrite nanoparticles were 48.8, 61.4, and 84.4 mW/g and decreased to 32.0, 45.2, and 83.3 mW/g after surface modification at the AMF strength of 150, 200, and 250 Oe, respectively.