Researcher:
Yağan, Rawana

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PhD Student

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Rawana

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Yağan

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Yağan, Rawana

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2020 - 20223

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Researcher Of Publications: search.filters.isAuthorOfPublication.19b3de0c-63d3-401f-81fb-6c475a917674

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    Damping and magnetic uniaxial anisotropy dependence of transient spin waves and mode type in magnetic nanowires
    (Institute of Electrical and Electronics Engineers Inc., 2020) Department of Electrical and Electronics Engineering; N/A; Onbaşlı, Mehmet Cengiz; Yağan, Rawana; Faculty Member; PhD Student; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 258783; N/A
    Patterned nanowires could enable tunable spin wave filters, logic and frequency multiplier devices. Using micromagnetic models, we investigate the effect of Gilbert damping and uniaxial anisotropy constant (K1) on the supported spin wave mode types, spatial and temporal transmission profile for a fixed finite patterned nanowire geometry under external DC and RF magnetic fields. Increasing damping constant leads to a shorter mode propagation length due to higher loss and flipping of the spin wave mode due to precession instability. Increasing K1 from -10-5 to 105 J·m-3also flips the mode and extends precession times. We further study the effect of changing the sample's initial magnetization orientation on the temporal and spectral responses. Anisotropy and damping engineering in patterned nanostructures could help build controlled spin wave filters, mode converters and multipliers.
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    PublicationOpen Access
    Steady state entanglement of distant nitrogen-vacancy centers in a coherent thermal magnon bath
    (American Physical Society (APS), 2022) Köse, Emre; Department of Physics; Department of Electrical and Electronics Engineering; Onbaşlı, Mehmet Cengiz; Müstecaplıoğlu, Özgür Esat; Ullah, Kamran; Yağan, Rawana; Faculty Member; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; 258783; 1674; N/A; N/A
    We investigate steady state entanglement (SSE) between two nitrogen-vacancy (NV) center defects in a diamond host on an ultrathin yttrium iron garnet (YIG) strip. We determine the dephasing and dissipative interactions of the qubits with the quanta of spin waves (magnon bath) in the YIG depending on the qubit positions on the strip. We show that the magnon's dephasing effect can be eliminated, and we can transform the bath into a multimode displaced thermal state using external magnetic fields. Entanglement dynamics of the qubits in such a displaced thermal bath have been analyzed by deriving and solving the master equation. An additional electric field is considered to engineer the magnon dispersion relation at the band edge to control the Markovian character of the open system dynamics. We determine the optimum geometrical parameters of the system of distant qubits and the YIG strip to get SSE. Furthermore, parameter regimes for which the shared displaced magnon bath can sustain significant SSE against the local dephasing and decoherence of NV centers to their nuclear spin environments have been determined. Along with SSE, we investigate the steady state coherence (SSC) and explain the physical mechanism of how delayed SSE appears following a rapid generation and sudden death of entanglement using the interplay of decoherence-free subspace states, system geometry, displacement of the thermal bath, and enhancement of the qubit dissipation near the magnon band edge. A nonmonotonic relation between bath coherence and SSE is found, and critical coherence for maximum SSE is determined. Our results illuminate the efficient use of system geometry, band edge in bath spectrum, and reservoir coherence to engineer system-reservoir interactions for robust SSE and SSC.
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    PublicationOpen Access
    Engineered magnetization dynamics of magnonic nanograting filters
    (Multidisciplinary Digital Publishing Institute (MDPI), 2021) Katmış, Ferhat; Department of Electrical and Electronics Engineering; Onbaşlı, Mehmet Cengiz; Yağan, Rawana; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 258783; N/A
    Magnonic crystals and gratings could enable tunable spin-wave filters, logic, and frequency multiplier devices. Using micromagnetic models, we investigate the effect of nanowire damping, excitation frequency and geometry on the spin wave modes, spatial and temporal transmission profiles for a finite patterned nanograting under external direct current (DC) and radio frequency (RF) magnetic fields. Studying the effect of Gilbert damping constant on the temporal and spectral responses shows that low-damping leads to longer mode propagation lengths due to low-loss and high-frequency excitations are also transmitted with high intensity. When the nanowire is excited with stronger external RF fields, higher frequency spin wave modes are transmitted with higher intensities. Changing the nanowire grating width, pitch and its number of periods helps shift the transmitted frequencies over super high-frequency (SHF) range, spans S, C, X, Ku, and K bands (3–30 GHz). Our design could enable spin-wave frequency multipliers, selective filtering, excitation, and suppression in magnetic nanowires.