有限温度下三角绝缘铁磁体的磁振子软化

Magnon Softening of Two-Dimensional Triangular Insulating Ferromagnet at Finite Temperature

在二维绝缘铁磁系统基础上建立了一个磁振子声子的相互作用模型.利用格林函数方法研究了磁振子声子相互作用下的三角绝缘铁磁体的磁振子谱;计算了布里渊区的主要对称点线上的磁振子色散曲线;比较了纵向声子与横向声子对磁振子谱的软化与磁振子谱线增宽的影响;讨论了各项参数以及温度的变化对磁振子谱的软化与磁振子谱线增宽的影响.得到了如下结论:①越接近布里渊区边界,磁振子声子耦合越强,自旋劲度系数D越小,材料的德拜温度ΘD越小,在铁磁相变温度Tc以下,随温度的升高,磁振子软化越明显;②离Γ点越远,磁振子软化越明显,谱线增宽越强,磁振子能谱的振荡与磁振子声子耦合强度无关;③在Σ线(包括Γ,M点)与Z线(包括M,K点)上,纵向声子比横向声子对磁振子的软化作用更大·

A magnon-phonon interaction model is developed on the basis of two-dimensional triangular insulating ferromagnet. The magonon spectrum is studied through Matsubara-Green function, and the magnon dispersion curve is calculated on the main symmetric point and line in Brillouin zone for different parameters in the system. It is concluded that at the boundary of Brillouin zone magnon linewidth broadening and magnon softening are both enhanced. The influences of longitudinal and transverse phonon on magnon spectrum softening and linewidth broadening are compared and discussed, as well as the influences of other relevant parameters and temperature change. The following conclusions are thus drawn: ① The closer the magnons come to the boundary of Brillouin zone, the more intense the magnon-phonon coupling and the clearer the magnon softening; ② The vibration of magonon spectrum is irrelevant to the intense of magnon-phonon coupling; ③ The smaller the stiffness constant of spin and the lower the Debye temperature Θ_D of the material, the clearer the magnon softening; ④ Below the transition temperature (T_c) of ferromagnetic, the higher the temperature, the clearer the magnon softening; ⑤ On the Σ line(including the point Γ,M) and Z line(including the point M,K), the longitudinal phonon have greater influence on magnon softening than the transverse one.