Control of the Magnetization of Bubble Garnets by Annealing

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Abstract
It is known that the magnetization of Ga‐ or Al‐substituted garnets can be reversibly altered by annealing and quenching. These treatments result in a redistribution of the substituted ions between the tetrahedral and octahedral iron sites. Changes of 4πMs by about 100 G can be achieved in bubble materials such as Eu2Er1Fe4.3Ga0.7O12. In an oxygen ambient, these changes occur in a few minutes at high temperatures such as 1200°C but require many hours at low temperatures such as 700°C. The times required for the low‐temperature anneals have been reduced by roughly two orders of magnitude by the use of a ``forming‐gas'' ambient. The anneals in this H2–N2 ambient do not result in major changes of the noncubic anisotropies of flux grown or LPE bubble garnets. This indicates that this anisotropy is not associated with the presence of Fe4+ions which would be reduced to Fe3+ by the anneals. The use of this low‐temperature annealing procedure to tailor the magnetization of bubble garnets along with the previously reported high‐temperature annealing to control growth‐induced noncubic anisotropy can be very useful for bubble device research and development.