Theory of Surface Spin Waves on a Pure Exchange Ferromagnet

Theory of Nonlinear Surface Spin Waves on a Pure Exchange Ferromagnet

Yan Xu¹, Gang Su², Desheng Xue¹, Zhaoyang Chen³ and Fa-Shen Li¹

¹ Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou, 730000, China

² Department of Physics, Graduate School at Beijing, University of Science and Technology of China, Chinese Academy of Sciences, Beijing, 100039, China

³ Theoretische Physik I, Ruhr Universität Bochum, Bochum, D-44780, Germany

Received 20 December 2000

Abstract

In terms of the total energy of a ferromagnet and the Landau–Lifshitz equation, the nonlinear surface spin waves in a ferromagnet with pure nonuniform exchange anisotropies are studied. It is found that the nonlinear dispersion relation for these waves is modified by the nonuniform exchange anisotropy comstants, and the nonlinear excitation appears as surface magnetic solitons localized near the surface of a crystal. A two-dimensional nonlinear Schrödinger equation for the spin–wave envelope is obtained and the conditions for the existence of a single soliton solution are discussed.