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Magnonic band structure investigation of one-dimensional bi-component magnonic crystal waveguides.

Ma FS, Lim HS, Zhang VL, Ng SC, Kuok MH - Nanoscale Res Lett (2012)

Bottom Line: Our results show that the widths and center frequencies of the bandgaps are controllable by the component materials, the stripe widths, and the orientation of the applied magnetic field.One salient feature of the bandgap frequency plot against stripe width is that there are n-1 zero-width gaps for the nth bandgap for both transversely and longitudinally magnetized waveguides.Additionally, the largest bandgap widths are primarily dependent on the exchange constant contrast between the component materials of the nanostructured waveguides.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National University of Singapore, Singapore, 117542, Singapore. phylimhs@nus.edu.sg.

ABSTRACT
The magnonic band structures for exchange spin waves propagating in one-dimensional magnonic crystal waveguides of different material combinations are investigated using micromagnetic simulations. The waveguides are periodic arrays of alternating nanostripes of different ferromagnetic materials. Our results show that the widths and center frequencies of the bandgaps are controllable by the component materials, the stripe widths, and the orientation of the applied magnetic field. One salient feature of the bandgap frequency plot against stripe width is that there are n-1 zero-width gaps for the nth bandgap for both transversely and longitudinally magnetized waveguides. Additionally, the largest bandgap widths are primarily dependent on the exchange constant contrast between the component materials of the nanostructured waveguides.

No MeSH data available.


Related in: MedlinePlus

Dispersion relations for transversely magnetized MCWs. (a) 16Fe/4Ni, (b) 16Fe/4Py, (c) 16Py/4Ni, (d) 16Co/4Ni, (e) 16Co/4Py, and (f) 16Co/4Fe MCWs under a H = 600 mT field applied along the y axis. The dotted lines indicate the Brillouin zone boundaries q = nπ/a, and the first, second, and third bandgaps are denoted by the red-, green-, and blue-shaded regions, respectively. The intensities of the SWs are represented by color scale.
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Figure 2: Dispersion relations for transversely magnetized MCWs. (a) 16Fe/4Ni, (b) 16Fe/4Py, (c) 16Py/4Ni, (d) 16Co/4Ni, (e) 16Co/4Py, and (f) 16Co/4Fe MCWs under a H = 600 mT field applied along the y axis. The dotted lines indicate the Brillouin zone boundaries q = nπ/a, and the first, second, and third bandgaps are denoted by the red-, green-, and blue-shaded regions, respectively. The intensities of the SWs are represented by color scale.

Mentions: For the transversely magnetized waveguides (see Figure 1a), the calculated SW dispersion curves along the longitudinal symmetry axis of 16Fe/4Ni, 16Fe/4Py, 16Py/4Ni 16Co/4Ni, 16Co/4Py, and 16Co/4Fe MCWs for H = 600 mT are shown in Figure 2. Due to the effect of width confinement [22-24], the dispersion curves are characterized by a lower frequency limit, viz. 32.0 GHz for 16Fe/4Ni, 31.5 GHz for 16Fe/4Py, 21.0 GHz for 16Py/4Ni, 25.0 GHz for 16Co/4Ni, 43.0 GHz for 16Co/4Py, and 21.5 GHz for 16Co/4Fe MCWs. These values correspond to the minimum frequency of the lowest allowable SW modes propagating through the respective waveguides. In contrast to the single monotonic dispersion curve of the isolated nanostripes [22], the periodic character of the three dispersion branches of the MCWs, calculated up to the third Brillouin zone (BZ), is evident from Figure 2. The dispersion curves are observed to be folded and exhibit bandgaps at the BZ boundaries (q = nπ/a, n = 1, 2, and 3) due to the periodic modulation of the material magnetic properties along the SW propagation direction. For the 16Fe/4Ni MCW, the first three bandgaps with respective widths of 6.0, 31.5, and 51.5 GHz exhibited at the BZ boundaries are shown in Figure 2a. Another notable feature is the variation of the SW mode intensities of the three branches over the three BZs, which are proportional to the squared Fourier transform of the dynamic magnetization [25]. The lowest branch has the maximum intensity in the first BZ, the second one in the second BZ, and so on. This is a consequence of the Umklapp process, which involves the reciprocal lattice vector G (G = n2π/a) [11]. By comparing the widths and center frequencies of the bandgaps for the six MCWs studied as shown in Figure 2a,b,c,d,e,f, it is interesting to note that the width and center frequencies of bandgaps are dependent on the component materials of the MCWs.


Magnonic band structure investigation of one-dimensional bi-component magnonic crystal waveguides.

Ma FS, Lim HS, Zhang VL, Ng SC, Kuok MH - Nanoscale Res Lett (2012)

Dispersion relations for transversely magnetized MCWs. (a) 16Fe/4Ni, (b) 16Fe/4Py, (c) 16Py/4Ni, (d) 16Co/4Ni, (e) 16Co/4Py, and (f) 16Co/4Fe MCWs under a H = 600 mT field applied along the y axis. The dotted lines indicate the Brillouin zone boundaries q = nπ/a, and the first, second, and third bandgaps are denoted by the red-, green-, and blue-shaded regions, respectively. The intensities of the SWs are represented by color scale.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475054&req=5

Figure 2: Dispersion relations for transversely magnetized MCWs. (a) 16Fe/4Ni, (b) 16Fe/4Py, (c) 16Py/4Ni, (d) 16Co/4Ni, (e) 16Co/4Py, and (f) 16Co/4Fe MCWs under a H = 600 mT field applied along the y axis. The dotted lines indicate the Brillouin zone boundaries q = nπ/a, and the first, second, and third bandgaps are denoted by the red-, green-, and blue-shaded regions, respectively. The intensities of the SWs are represented by color scale.
Mentions: For the transversely magnetized waveguides (see Figure 1a), the calculated SW dispersion curves along the longitudinal symmetry axis of 16Fe/4Ni, 16Fe/4Py, 16Py/4Ni 16Co/4Ni, 16Co/4Py, and 16Co/4Fe MCWs for H = 600 mT are shown in Figure 2. Due to the effect of width confinement [22-24], the dispersion curves are characterized by a lower frequency limit, viz. 32.0 GHz for 16Fe/4Ni, 31.5 GHz for 16Fe/4Py, 21.0 GHz for 16Py/4Ni, 25.0 GHz for 16Co/4Ni, 43.0 GHz for 16Co/4Py, and 21.5 GHz for 16Co/4Fe MCWs. These values correspond to the minimum frequency of the lowest allowable SW modes propagating through the respective waveguides. In contrast to the single monotonic dispersion curve of the isolated nanostripes [22], the periodic character of the three dispersion branches of the MCWs, calculated up to the third Brillouin zone (BZ), is evident from Figure 2. The dispersion curves are observed to be folded and exhibit bandgaps at the BZ boundaries (q = nπ/a, n = 1, 2, and 3) due to the periodic modulation of the material magnetic properties along the SW propagation direction. For the 16Fe/4Ni MCW, the first three bandgaps with respective widths of 6.0, 31.5, and 51.5 GHz exhibited at the BZ boundaries are shown in Figure 2a. Another notable feature is the variation of the SW mode intensities of the three branches over the three BZs, which are proportional to the squared Fourier transform of the dynamic magnetization [25]. The lowest branch has the maximum intensity in the first BZ, the second one in the second BZ, and so on. This is a consequence of the Umklapp process, which involves the reciprocal lattice vector G (G = n2π/a) [11]. By comparing the widths and center frequencies of the bandgaps for the six MCWs studied as shown in Figure 2a,b,c,d,e,f, it is interesting to note that the width and center frequencies of bandgaps are dependent on the component materials of the MCWs.

Bottom Line: Our results show that the widths and center frequencies of the bandgaps are controllable by the component materials, the stripe widths, and the orientation of the applied magnetic field.One salient feature of the bandgap frequency plot against stripe width is that there are n-1 zero-width gaps for the nth bandgap for both transversely and longitudinally magnetized waveguides.Additionally, the largest bandgap widths are primarily dependent on the exchange constant contrast between the component materials of the nanostructured waveguides.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, National University of Singapore, Singapore, 117542, Singapore. phylimhs@nus.edu.sg.

ABSTRACT
The magnonic band structures for exchange spin waves propagating in one-dimensional magnonic crystal waveguides of different material combinations are investigated using micromagnetic simulations. The waveguides are periodic arrays of alternating nanostripes of different ferromagnetic materials. Our results show that the widths and center frequencies of the bandgaps are controllable by the component materials, the stripe widths, and the orientation of the applied magnetic field. One salient feature of the bandgap frequency plot against stripe width is that there are n-1 zero-width gaps for the nth bandgap for both transversely and longitudinally magnetized waveguides. Additionally, the largest bandgap widths are primarily dependent on the exchange constant contrast between the component materials of the nanostructured waveguides.

No MeSH data available.


Related in: MedlinePlus