Amplified Ferrimagnetic Echoes in Single Crystal-Polycrystal YIG Composites

Abstract

To clarify the conditions for generation of amplified Hahn‐type echoes in ferrimagnets, experiments were conducted with composite samples formed by imbedding single crystal YIG wafers at various positions at and near the end of a poly crystalline YIG bar of similar cross section and 4πM value. The poly crystalline component provided the internal field and field gradient needed for echo formation but did not contribute directly to the signal because of its broad linewidth. As the single crystal wafer was moved along the magnetic axis of the sample the effects of internal field, field gradient, and microwave coupling on the echo were studied. The results determine the effective volume of the sample producing the echo, indicate thatthis volume is diminished by nonuniformities in the surface demagnetizing field, and show that an axial gradient on the order of 300 Oe/mm is needed for good echo formation and amplification.