| 초록 |
Exchange bias is a very exceptional property in order to develop functional materials for magnetic data storage and high frequency devices. In the present work, Fe-M, M: Ni, Co ferromagnetic heterometallic nanoparticles (NPs) were prepared using sodium borohydride assisted co-precipitation technique with subsequent annealing in a simple box furnace at 210°C for 4 hrs. The synthesized NPs were investigated for the presence of exchange bias using various characterization techniques viz. x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and dc-magnetization. The XRD patterns indicated the formation of face centered cubic and body centered cubic phases of Fe-Ni and Fe-Co respectively in addition to the impurity peaks corresponding to metal hydroxides and pure metals. The crystallite sizes, calculated using Scherrer’s formula, were found to be in nm range. The Fe-SEM micrographs of Fe-Co NPs manifested amalgamated aspheric morphology, while that of Fe-Ni NPs displayed dumbbell-shaped agglomerates of particles. Raman spectroscopic analysis confirmed the presence of impurity phases. The field dependent magnetization (MH) hysteresis loops, measured at 300K and 50K temperature, revealed a weak ferromagnetic behavior indicating soft magnetic nature of the heterometallic NPs. The reduction in temperature was found to enhance the value of saturation magnetization. The MH-hysteresis loops measured at 50K temperature under the conditions of field cooled (FC) and zero field cooled (ZFC) exhibited horizontal shift which points towards the presence of exchange bias. The value of exchange bias field (Heb) was found to be ~ 14Oe in Fe-Ni NPs, whereas, Fe-Co nanoparticles demonstrated a value of ~ 47 Oe. These results are promising owing to the ferromagnetic nature of these heterometallic nanoparticles in addition to the values of Heb obtained at 50K temperature. The exchange bias was also validated from the temperature dependent FC and ZFC magnetization curves that exhibit bifurcation below 350K temperature which make these ferromagnetic heterometallic NPs favorable for technological applications. |
