Effective defects in magnonic crystals
18 Nov 2014 Magnonic materials could make possible realization of energy-efficient CPUs that generate no heat, by avoiding the Joule-heating problem.
The controlled introduction of defects in materials can radically alter their properties in desired ways, which is perhaps best exemplified by the enhanced electrical conductivity of semiconductors arising from chemical impurities in them. Properties of magnonic crystals (MCs), e.g. periodic arrays of nanostripes, can also be controlled or enhanced by the presence of defects which are deviations from the artificial crystal periodicity.
A team led by Prof KUOK Meng Hau from the Department of Physics in NUS has mapped the band structure of a nanostructured magnonic crystal with defects. Using the technique of Brillouin light scattering, the dispersion relations of spin waves in MCs, composed of arrays of alternating cobalt and Permalloy (Ni80Fe20) nanostripes, with defects have been experimentally observed for the first time. Importantly, the Brillouin group demonstrated that the magnon band structure (see Figure) of these materials can be tuned by varying the defect size. The controlled introduction of defects in MCs could pave the way for energy-band engineering and for producing the building blocks for integrated magnonic circuits. For instance, defect MCs could be exploited for the fabrication of tunable spin-wave filters and logic gates, which are of fundamental importance to magnonic applications.
The figure shows the magnon band structures of the Co/Permalloy MCs with defect Permalloy stripes. The dashed vertical lines indicate the Brillouin zone boundary. Measured Brillouin data are indicated by red squares, while finite-element and micromagnetic-simulated data are shown as black circles and green lines, respectively. Inset: SEM image of a portion of the crystal showing two defect stripes. [Image credit: KUOK Meng Hau]
K Di, VL Zhang, MH Kuok, HS Lim, SC Ng, K Narayanapillai, H Yang, “Observation of the band structures of defect magnonic crystals” Physical Review B 90 (2014) 060405(R).