Dipartimento di Fisica e Scienze della Terra, CNISM Unità di Ferrara, Università di Ferrara, Via Saragat 1, I-44122 Ferrara, Italy.
J Phys Condens Matter. 2013 Aug 21;25(33):336002. doi: 10.1088/0953-8984/25/33/336002. Epub 2013 Jul 24.
Soft magnonic modes in permalloy antidot lattices with a fixed lattice constant a = 420 nm and circular hole diameters ranging between 140 and 260 nm are investigated both experimentally and theoretically. The frequency dependence of magnonic modes on the magnetic field intensity, applied along the vertical rows of holes, was measured by Brillouin light scattering from thermally excited spin waves. All the detected modes exhibit a monotonic frequency evolution with respect to the applied magnetic field, with the exception of the two lowest frequency modes which become soft at a given critical field and exhibit a finite frequency gap. It has been shown, by means of micromagnetic simulations based on the dynamical matrix method, that the mode softening is strictly related to the rotation of the static magnetization from the hard to the easy axis marking a reorientational and continuous phase transition. In addition, the different frequency trend of the fundamental mode and of the corresponding mode localized along the horizontal rows of holes as a function of the aspect ratio is explained in terms of the opposite demagnetizing field experienced by the two modes.
具有固定晶格常数 a=420nm 和直径在 140nm 到 260nm 之间的圆形孔的坡莫合金点阵中的软磁振子模式，通过从热激发自旋波的布里渊光散射实验和理论都进行了研究。通过测量沿孔的垂直行施加的磁场强度对磁振子模式的频率依赖性，从热激发自旋波的布里渊光散射实验和理论都进行了研究。所有检测到的模式都表现出与施加磁场单调的频率演化，除了两个最低频率模式，它们在给定的临界磁场下变软，并表现出有限的频率间隙。通过基于动态矩阵方法的微磁模拟表明，模式软化与静态磁化从硬轴到易轴的旋转严格相关，标志着一种重定向和连续的相转变。此外，基本模式和对应模式沿孔的水平行的频率趋势随纵横比的变化，可以根据两种模式经历的相反退磁场来解释。
