Second-Order Magnetoelastic Properties of Yttrium Iron Garnet

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Abstract
Second‐order (in strain) magnetoelastic properties of yttrium iron garnet (YIG) have been studied using an ultrasonic technique. The group velocity of selected small‐amplitude magnetoelastic (dominantly elastic) modes in single‐crystal specimens has been measured at a frequency of 30 Mc/sec as a function of magnetic field strength and magnetization orientation. In this manner, first‐order and second‐order magnetoelastic constants and second‐order ``morphic'' constants have been completely determined for YIG. This work reports the first evaluation of second‐order magnetoelastic constants and morphic constants. All results have been interpreted using finite deformation magnetoelastic theory. Small strain magnetoelastic theory, valid only to first order in small quantities, leads to incorrect results in the treatment of second‐order effects.