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

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.