Delay of Microwave Signals in Single-crystal Yttrium Iron Garnet†

Abstract

ABSTRACT A first-order theory with experimental results is presented to describe the magnetoelastic propagation effects in single-crystal yttrium iron garnet. These crystals have been found to possess extremely low magnetic and acoustic loss characteristics. When cut in the shape of a cylindrical rod and immersed in an external magnetic field, the internal magnetic field is found to be a function of position within the rod. If, in addition, the crystal is illuminated with electromagnetic energy at microwave frequencies, spin waves can be excited. The non-uniformity of the internal magnetic field permits these spin waves to excite elastic shear waves. Both the elastic and spin waves propagate at velocities at least four orders of magnitude less than the speed of light; the exact group velocity of the spin waves depends on the magnitude of the magnetic field. By exciting such waves in yttrium iron garnet, the incident microwave signal can be delayed as much as 14 microsec in a 1 cm length rod. The low loss ...