Grain boundaries and growth kinetics of polycrystalline ferrimagnetic oxides with chemical additives

Grain boundaries and grain growth kinetics of two ferrimagnetic oxides, Y2Gd1Fe5O12 and Li0.3Zn0.4Fe2.3O4, modified by a sol–gel particulate coating process were investigated on the basis of their microstructural characteristics. Interestingly, the addition of small amounts of MnO2 and SiO2 using the sol–gel coating process led to different results for the two magnetic materials. In the case of Y2Gd1Fe5O12, the additives had a role as a grain growth inhibitor because Si-rich precipitates were segregated along the grain boundary and exerted a drag force against grain boundary movement. On the other hand, the same additives acted as an accelerator for grain growth by forming a glassy phase at the grain boundaries for Li0.3Zn0.4Fe2.3O4. The results were analyzed quantitatively by calculating activation energies for grain growth and grain boundary mobilities. For example, the calculated grain boundary mobilities, i.e., 5.6×10−15 m3/N s at 1400 °C for Y2Gd1Fe5O12 and 22.3×10−15 m3/N s at 1150 °C for Li0.3Zn0.4...