Mat. Res. Bull., Vol. 17, pp. 957-962, 1982. Printed in the USA. 0025-5408/82/080957-06503.00/0 Copyright (c) 1982 Pergamon Press Ltd. SUB-MICRON YIG MICROSTRUCTURE AND FERROMAGNETIC RESONANCE L~NEWIDTH S.G. Gokarn, V.R. Palkar and M.S. Multani ~' Materials Science Group, Tata Institute of Fundamental Research HomiBhabha Road, Bombay - 400005, India (Received December 22, 1981; Refereed) ABSTRACT It has been shown possible to push the grain size of siatered YIG below 1 micron by using 400/~ YIG microcrystals and pressure sinteriag. This has implications for moving up the threshold for nonlinear spinwave excitation with a microwave pump. The ferromagnetic resonance liaewidth has beer shown to be inversely dependent on grain size on a log-log scale. Introduction Yttrium iron garnet, {Y3]¢ [Fez~]~ (Fe3 ~ )c/.Olz and its various solid solutions have been found to be very useful in microwave devices. The main reason for this is the extremely low ferroma~etic resonance linewidths that these materials exhibit. It has been well established now that the microstructure of the material plays a~ important role in the high- power microwave applications, Thus, polycrystalline YIG with finer grains can be used at much higher power levels than an identical material with coarser grains (I). I~deed, Patton has reported an inverse log-log dependence of the parallel pump sp~wave lisewidth A H k as a function of average grain diameter decreasing up to 1 micron (Z).-~ 0 The above fact has instigated several groups to obtain materials with finer grains and having nearly single-crystal densities. In spite of these efforts, the minimum grain size reported at almost theoreticaldensity is not less than I micron (2). In the present paper we report the achievement of sub-micron microstructure at almost theoretical density, and the variation of ferro- magnetic resonance liaewidth with grain size. To whom all correspondence may be addressed. 957