Influence of Jahn-Teller Ions on the Acoustic and Magnetic Properties of YIG

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Abstract
The presence of Mn3+ ions in YIG leads to a large low‐temperature acoustic loss and to a reduction in sound velocity. In the range of 1 to 15 Mc/sec, these effects increase rapidly with decreasing temperature. In addition, the presence of Mn3+ also gives rise to a large microwave loss which peaks at 37°K for 15 kMc/sec and at 58°K for 56 kMc/sec. In the range of 0 to 1 wt % Mn additions, both acoustic and microwave losses increase monotonically with Mn content. The observed effects are attributed to relaxation between the three possible directions of the Jahn‐Teller distortion. At high temperatures the relaxation time becomes characteristic of thermal activation over a potential barrier. At low temperatures the relaxation time becomes independent of temperature which is characteristic of quantum‐mechanical tunneling. A simple model gives a reasonable description of the observed results in YIG, and a comparison with Mn3+ in YAG or Ni3+ in corundum indicates that the remaining discrepancies may be attributed to the exchange field and magnetostrictive effects. The latter are substantially enhanced by the presence of Mn.

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