LATTICE DISTORTION EFFECTS WITHIN THE GENERALIZED TRANSVERSE ISING-MODEL

A qualitative analysis of lattice vibration effects including lattice distortions, spin-phonon interaction, and phonon anharmonicity is give n within the extended transverse Ising spin model (TIM). It is argued that the rigid-lattice TIM is a credible model for real crystal in the sense that no new anisotropic-type interactions emerge due to higher- order lattice distortions. Instead of the known first-order Kobayashi model a new effective second-order nonrigid-lattice TIM is proposed. R ecent developments in the TIM spin dynamics are briefly discussed.