Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences , Block JD, Sector III, Salt Lake, Kolkata 700 106, India.
Institute of Engineering and Management , Sector V, Salt Lake, Kolkata 700 091, India.
ACS Nano. 2017 Sep 26;11(9):8814-8821. doi: 10.1021/acsnano.7b02872. Epub 2017 Aug 14.
Efficient tunability of magnonic spectra is demonstrated in two-dimensional ferromagnetic antidot lattices with different lattice constants arranged in the octagonal lattice which can be considered as quasi-periodic magnonic crystals due to the presence of broken translational symmetry. The precessional dynamics of these samples are investigated in the frequency domain with the help of broadband ferromagnetic resonance spectrometer. A rich variation in the spin wave spectra is observed with the variation of lattice constant as well as the strength and orientation of the bias magnetic field. A broad band of spin wave modes are observed for the denser array, which finally converges to two spin wave modes for the sparsest one. In addition to this, the most intense spin wave frequency shows an 8-fold anisotropy with a superposition of weak 4- and 2-fold anisotropy, which arises due to the angular variation of the magnetostatic field distribution at different regions of the octagonal lattice. Micromagnetic simulations qualitatively reproduce the experimentally observed modes, and the simulated mode profiles reveal the presence of different types of extended and quantized standing spin wave modes in these samples. The observations are important for the tunable and anisotropic propagation of spin waves in magnonic crystal based devices.
在具有不同晶格常数的二维铁磁型点阵中，通过排列在八边形晶格中，展示了磁振子谱的高效可调谐性，由于存在破坏平移对称性的现象，这些点阵可以被视为准周期的磁振子晶体。借助宽带铁磁共振谱仪，在频域中研究了这些样品的进动动力学。随着晶格常数以及偏置磁场的强度和方向的变化，观察到了自旋波谱的丰富变化。对于更密集的阵列，观察到了一个宽带的自旋波模式，最终对于最稀疏的一个，收敛为两个自旋波模式。除此之外，最强烈的自旋波频率表现出 8 倍各向异性，叠加有较弱的 4 倍和 2 倍各向异性，这是由于在八边形晶格的不同区域中，静磁场分布的角度变化引起的。微磁模拟定性地再现了实验观察到的模式，并且模拟的模式分布揭示了在这些样品中存在不同类型的扩展和量子化的驻波自旋波模式。这些观察结果对于基于磁振子晶体的器件中自旋波的可调谐和各向异性传播非常重要。
