SCATTERING OF ACOUSTIC PHONONS BY RARE-EARTH SUBSTITUTIONAL ATOMS IN YTTRIUM ALUMINUM GARNETS

The diffusive maxima of phonon signals, and in particular their arriva l times t(m) are examined for a number of solid solutions of rare eart h atoms in yttrium aluminum garnets. The phonon pulses are generated b y metallic films of the characteristic length l(h) heated by current p ulses to the temperature T-h slightly higher than the ambient temperat ure T. The injected phonons travel in wafers of the thickness L(z). Th ey are scattered by substitutional atoms of rare earth occupying the y ttrium dodecahedral sites, rare earth and yttrium atoms occupying the aluminum octahedral sites and by another lattice imperfections generat ed in the process of sample growing, The qualitative analysis based on our exact formula for the diffusion coefficient D allows us to extrac t the contribution of rare earth atoms substituting the Y atoms 2 to D . Considering the dependence of t(m)/L(z)(2) on the temperature and th e ratio l(h)/L(z) we conclude that D similar to T-h(-4) and that the e nergy of phonons forming the diffusive maxima ranges from 3.2 k(B)T(H) to 4.2 k(B)T(H), which is in reasonable agreement with the existing e stimates.