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

Grain boundaries and grain growth kinetics of two ferrimagnetic oxides, Y2G d1Fe5O12 and Li0.3Zn0.4Fe2.3O4, modified by a sol-gel particulate coating p rocess were investigated on the basis of their microstructural characterist ics. Interestingly, the addition of small amounts of MnO2 and SiO2 using th e sol-gel coating process led to different results for the two magnetic mat erials. In the case of Y2Gd1Fe5O12, the additives had a role as a grain gro wth inhibitor because Si-rich precipitates were segregated along the grain boundary and exerted a drag force against grain boundary movement. On the o ther hand, the same additives acted as an accelerator for grain growth by f orming a glassy phase at the grain boundaries for Li0.3Zn0.4Fe2.3O4. The re sults were analyzed quantitatively by calculating activation energies for g rain growth and grain boundary mobilities. For example, the calculated grai n boundary mobilities, i.e., 5.6 x 10(-15) m(3)/Ns at 1400 degrees C for Y2 Gd1Fe5O12 and 22.3 x 10(-15) m(3)/Ns at 1150 degrees C for Li0.3Zn0.4Fe2.3O 4, supported the microstructural observation. (C) 1999 American Institute o f Physics. [S0021-8979(99)37408-9].