Influence of Ho 3+ substitution on structural and magnetic properties of Mg–Mn ferrites

Polycrystalline nano-magnetic pure and Ho3+-substituted Mg–Mn ferrite [Mg0.90Mn0.10Fe(2−x)HoxO4 (x = 0, 0.1, 0.2, and 0.3)] nanoparticles were synthesized by sol–gel combustion method. The physicochemical properties of samples were analyzed using various characterization techniques such X-ray diffractometer, Fourier transform infrared spectroscopy (FTIR), Mossbaur spectroscopy, vibrating sample magnetometer, field emission scanning electron microscope (FESEM) to identify the crystalline phase, functional groups, surface morphology, and magnetic behavior. The structural studies revealed that all the compositions showed pure phase formation of ferrite nanoparticles without any secondary phases and exhibited a cubic crystalline structure with $$Fd\stackrel{-}{3}m$$ space group. FTIR spectra displayed the high-frequency peak observed at 554 cm−1 belonging to Fe–O bending, which confirmed the formation of pristine and Ho3+ modified spinel Mg–Mn ferrite nanoparticles. FESEM micrographs depicted the pseudo-spherical and granular morphology with agglomerated regions and energy dispersive X-ray spectra showed the elemental compositions present in the prepared nanoparticles confirming the high purity of the synthesized samples. EPR spectra illustrated the magnetic nature of pure and Ho3+-substituted Mg–Mn ferrite nanoparticles and displayed strong inter-dipolar interactions. Mossbauer spectra showed that the quadrupole shift increased with increasing Ho3+ content in the composition. All the compositions exhibited superparamagnetic behavior and it was observed that the value of saturation magnetization decreased with Ho3+ intrusion in the crystal framework of Mg–Mn ferrites as depicted by magnetic hysteresis loops. The observed results of the present study are significant and useful for their effective utilization in biosensing applications.