Probing of electric and magnetic properties of holmium doped iron oxide nanoparticles

Lanthanide based nanoparticles due to their high magnetic moments and efficient optical properties are potential candidates for various applications. In this paper we report holmium (Ho³⁺) ion doped iron oxide nanoparticles (NPs) with different concentrations; ⍺-Ho_xFe_2−xO₃ (x = 0.00, 0.03, 0.05 and 0.07) synthesized by sol–gel method. The synthesized NPs were studied for dielectric and magnetic properties and were thoroughly characterized using various analytical techniques such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), etc. The PXRD confirms hexagonal structure of pure and Ho³⁺ ion doped iron oxide NPs. The presence of Ho³⁺ ions was observed by EDS technique. The dielectric studies were carried out at (i) varying temperature (100–400 K) at constant frequency of 100 kHz and (ii) varying frequency (20 Hz–1000 kHz) at constant temperature of 298 K. Both temperature and frequency dependent dielectric studies shows increase in dielectric constant and decrease in dielectric loss with the increase in Ho³⁺ ion concentration in ⍺-Fe₂O₃ system. The high values of dielectric constant and low values of dielectric loss at higher frequencies makes these materials as potential candidates for microwave applications. Also the conductivity increases with increase in temperature in the systems studied, indicates semiconducting behavior and decrease in conductivity is observed with Ho³⁺ ion doping. The conductivity behavior follows Motts law, confirming the variable range hopping mechanism in all the synthesized systems. The magnetic studies shows that the addition of Ho³⁺ ions in ⍺-Fe₂O₃ lattice significantly modifies the magnetic properties. On comparing to pure phase, an increase in saturation magnetization was observed for all the samples with Ho³⁺ ion doping.