Fractal spectra in generalized Fibonacci one-dimensional magnonic quasicrystals

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• 作者：C.H.O. Costa^a ; M.S. Vasconcelos^b ; ^{manoelvasconcelos@yahoo.com.br} ; ^{mvasconcelos@ect.ufrn.br} ; P.H.R. Barbosa^c ; F.F. Barbosa Filho^c
• 关键词：Spin wave ; Magnonic crystal ; Quasiperiodic structure ; Fractal spectrum
• 刊名：Journal of Magnetism and Magnetic Materials
• 出版年：2012
• 期刊代码：31_03048853
• 类别：ph
• 出版时间：July, 2012
• 卷：324
• 期：14
• 页码：2315-2323
• 文件大小：1474 K

摘要

In this work we carry out a theoretical analysis of the spectra of magnons in quasiperiodic magnonic crystals arranged in accordance with generalized Fibonacci sequences in the exchange regime, by using a model based on a transfer-matrix method together random-phase approximation (RPA). The generalized Fibonacci sequences are characterized by an irrational parameter , which rules the physical properties of the system. We discussed the magnonic fractal spectra for first three generalizations, i.e., silver, bronze and nickel mean. By varying the generation number, we have found that the fragmentation process of allowed bands makes possible the emergence of new allowed magnonic bulk bands in spectra regions that were magnonic band gaps before, such as which occurs in doped semiconductor devices. This interesting property arises in one-dimensional magnonic quasicrystals fabricated in accordance to quasiperiodic sequences, without the need to introduce some deferent atomic layer or defect in the system. We also make a qualitative and quantitative investigations on these magnonic spectra by analyzing the distribution and magnitude of allowed bulk bands in function of the generalized Fibonacci number F_n and as well as how they scale as a function of the number of generations of the sequences, respectively.