An experimental and theoretical investigation of magnetic ordering in Yttrium Iron Garnet

Laser Raman backscattering was used to experimentally study the two magnon spectrum of yttrium iron garnet (YIG) as a function of temperature both below and above the ferrimagnetic Curie temperature of 550 K. Raman spectra were obtained from single crystals of YIG using a krypton-ion laser, a double grating monochromator, and a photon counting detection system. The first observation of three new second-order Raman peaks at frequencies of 893 + or - 15/cm, 115 + or - 15/cm and 1415 + or - 15/cm. The peak at 893 + or - 15/cm is attributed to delta S = 0, two magnon mixed optic branch scattering on the basis of the temperature dependence of its intensity while the other peaks are attributed to a two phonon scattering mechanism. The observed first-order phonon spectra are in excellent agreement with previously reported experimental spectra.