Tunability of Domain Structure and Magnonic Spectra in Antidot Arrays of Heusler Alloy

Sougata Mallick, Sucheta Mondal, Takeshi Seki, Sourav Sahoo, Thomas Forrest, Francesco Maccherozzi, Zhenchao Wen, Saswati Barman, Anjan Barman, Koki Takanashi, and Subhankar Bedanta

Phys. Rev. Applied 12, 014043 – Published 24 July 2019

Abstract

Materials suitable for magnonic crystals demand low magnetic damping and long spin-wave propagation distance. In this context $Co$ -based Heusler compounds are ideal candidates for magnonic based applications. In this work, antidot arrays (with different shapes) of epitaxial ${Co}_{2} {Fe}_{0.4} {Mn}_{0.6} Si$ Heusler-alloy thin films are prepared using e-beam lithography and sputtering technique. Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance analysis confirm the presence of dominant cubic and moderate uniaxial magnetic anisotropies in the thin film. Domain imaging via x-ray photoemission electron microscopy on the antidot arrays reveals chainlike switching or correlated bigger domains for different antidot shapes. Time-resolved MOKE microscopy is performed to study the precessional dynamics and magnonic modes of the antidots with different shapes. We show that the optically induced spin-wave spectra in such antidot arrays can be tuned by changing the shape of the holes. The variation in internal-field profiles, pinning energy barrier, and anisotropy modifies the spin-wave spectra dramatically within the antidot arrays with different shapes. We further show that by combining the magnetocrystalline anisotropy with the shape anisotropy, an extra degree of freedom can be achieved to control the magnonic modes in such antidot lattices.

Received 10 January 2019
Revised 28 April 2019

DOI:https://doi.org/10.1103/PhysRevApplied.12.014043

Physics Subject Headings (PhySH)

Magnetic anisotropy Magnonic crystals Spin waves Spintronics Ultrafast magnetization dynamics

Heusler alloy Nanostructures Thin films

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Sougata Mallick¹, Sucheta Mondal², Takeshi Seki^3,4, Sourav Sahoo², Thomas Forrest⁵, Francesco Maccherozzi⁵, Zhenchao Wen^3,4,†, Saswati Barman⁶, Anjan Barman², Koki Takanashi^3,4, and Subhankar Bedanta ^1,*

¹Laboratory for Nanomagnetism and Magnetic Materials (LNMM), School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, Odisha, India
²Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India
³Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
⁴Center for Spintronics Research Network, Tohoku University, Sendai 980-8577, Japan
⁵Diamond Light Source Ltd., Diamond House, Didcot, Oxfordshire OX11 0DE, United Kingdom
⁶Institute of Engineering and Management, Sector V, Salt Lake, Kolkata 700091, India

^*sbedanta@niser.ac.in
^†Present address: National Institute for Materials Science, Tsukuba 305-0047, Japan.

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Vol. 12, Iss. 1 — July 2019

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Images

Figure 1
(a),(b) RHEED images for TF along CFMS [100] and CFMS [110] directions. (c) XRD pattern for TF showing the CFMS, $Cr$ , and $Mg O$ peaks. The peak denoted by $*$ appearing around $38^{\circ}$ arises from the (200) diffraction of the $Mg O$ substrate with $Cu - K_{β}$ sources. (d) $M$ - $H$ curve for TF measured by VSM at room temperature along the easy, i.e., CFMS $[\bar{1} 10]$ direction.
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Figure 2
Hysteresis loops measured using micro-MOKE along CFMS $[\bar{1} 10]$ direction at room temperature for CA, SA, TA, and DA, shown in (a)–(d), respectively. The insets show the corresponding SEM images of the antidot samples.
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Figure 3
(a) SEM image of CA (circular antidot). (b)–(f) Domain images in CA measured by XPEEM (XMCD at the $Fe$ $L_{3}$ edge) at magnetic field pulses of $- 40.56$ , 5.07, 8.11, 9.13, and 40.56 mT, respectively. (g) SEM image of TA (triangular antidot). (h)–(l) Domain images in TA at field pulses of $- 40.56$ , 4.26, 4.46, 5.07, and 40.56 mT, respectively. Scale bars for the XPEEM images are the same for both samples, which are shown in (b),(h). The field is applied along the EA (CFMS $[\bar{1} 10]$ ) and the direction is shown in (l).
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Figure 4
(a)–(d) SW spectra obtained at $μ_{0} H = 153 mT$ from the experimental time-resoled Kerr rotation data for CA, SA, TA, and DA, respectively. (e)–(h) Simulated SW spectra for CA, SA, TA, and DA, respectively. The numbers corresponding to different modes are shown in the individual images. The images in the insets of (a)–(d) and (e)–(h) show the shape of a single hole in the antidot array obtained from SEM images and bitmap images considered in the simulation, respectively.
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Figure 5
Simulated power maps for different precessional modes as shown in Figs. 4–4 for circular, square, triangular, and diamond antidots, respectively. Phase profiles are shown inside the dashed box at the top right corner of the images. The color map for the power distribution is shown at the bottom of the image. The respective mode numbers as per Fig. 4 is shown in the right side of the image. The quantization numbers are calculated from the profiles within the blue-colored boxed regions as shown in (g),(j). An external magnetic field of 153 mT is applied along the easy axis (CFMS $[\bar{1} 10]$ ) as shown in the figure.
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Figure 6
(a) Magnetostatic field distribution of different antidot lattices is shown. The line scans of $y$ component (CFMS $[\bar{1} 10]$ ) of the magnetostatic field (b) across the antidots [orange dashed line in (a)] and (c) along the channel between the two columns of antidots [green dotted line in (a)]. The magnified view of the minima in the line scan is shown at the inset of (b). The hollow boxes in (c) represent regions I and II as highlighted in (a). The color bar is presented at the bottom of (a).
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