Ferroic ordering and charge-spin-lattice order coupling in Gd doped Fe$_{3}$O$_{4}$ nanoparticles

Rare earth doped spinels have been extensively studied for their potential applications in magneto-optical recording and as MRI contrast agents. In the present study, we have investigated the effect of gadolinium doping (1-5 at.{\%}) on the magnetic and dielectric properties of Fe$_{3}$O$_{4\, }$nanoparticles synthesized by the chemical co-precipitation method. The structure and morphology of the as-synthesized gadolinium doped Fe$_{3}$O$_{4\, }$(Gd-Fe$_{3}$O$_{4})$ nanoparticles were characterized by XRD, SEM and TEM, and the magnetic properties were measured by a Quantum Design physical property measurement system. We find that the penetration of excess Gd$^{3+}$ ions into Fe$_{3}$O$_{4}$ spinel matrix significantly influences the average crystallite size and saturation magnetization in Gd-Fe$_{3}$O$_{4}$. The average crystallite size, estimated from XRD using Scherrer equation, increases with increasing Gd doping percentage and the saturation magnetization drops monotonically with excess Gd$^{3+}$ ions. Interestingly, Gd- Fe$_{3}$O$_{4\, }$develops enhanced ferroelectric ordering at low temperatures. The details of the temperature dependent dielectric, ferroelectric and magnetocapacitance measurements to understand the onset of charge-spin-lattice coupling in Gd-Fe$_{3}$O$_{4\, }$ system will be presented.