Microdischarge Treatment of Iron-Doped YAG

In order to investigate the role of crystal defects in dilute magnetism in more detail, a nonconventional method for creating more defects (MD/CF, see below) and a quite conventional technique for decreasing their number (annealing in air atmosphere) were used. 

The effect of modulation of crystal defects is presented by the recently developed method of microdischarge between carbon felts [12]. Carbon felts prepared at 2500 °C have the following characteristics. The specific area is as large as 1.6 g and their small electric resistance is about 50 mil cm. Carbon felts with small diameters (about I p,m) have so low dielectric resistance that they can absorb and reflect microwaves effectively. The discharge between carbon felts occurs easily with a small gap as shown in Fig. 25.10. 

Schematic picture of the furnace for microwave discharge generated between carbon felts and picture of carbon felts. (Reproduced with permission of the Japan Society of Powder and Powder Metallurgy.) 

X-ray diffractograms of Y3Al5 xFexO,2 after preparation and after the MD/CF treatment. The inset shows the shift of the most intense line due to the MD/ CF treatment. 

As shown in Fig. 25.14, the lackof direct correspondence between any Mossbauer component and the ferromagnetic component of the bulk ferromagnetism suggests that the latter in these garnets may arise not only from the rare doped magnetic iron ions but also from the crystal defects. While the MD/CF treatment increased the ferromagnetic moment in both samples, the magnetic sextets did not increase in the Mossbauer spectra in the case of x = 0.02, the sextets even shrink to their half. 

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