The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
K Morrison - One of the best experts on this subject based on the ideXlab platform.
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spin seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid state method
EPL, 2019Co-Authors: G Venkat, T A Rose, Christopher D W Cox, G B G Stenning, Andrew J Caruana, K MorrisonAbstract:We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets prepared by the solid-state method, where the choice of the sintering temperature can lead to mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate the saturation magnetization from magnetometry and to extract the spin Wave Damping α . The lowest Damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE) coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline samples for thermomagnetic applications.
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Spin Seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid-state method [Letter]
2019Co-Authors: G Venkat, T A Rose, G B G Stenning, Andrew J Caruana, Chris Cox, K MorrisonAbstract:We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets prepared by the solid-state method, where the choice of the sintering temperature can lead to mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate the saturation magnetization from magnetometry and to extract the spin Wave Damping α. The lowest Damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE) coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline samples for thermomagnetic applications
T Van Doorsselaere - One of the best experts on this subject based on the ideXlab platform.
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Wave Damping observed in upwardly propagating sausage mode oscillations contained within a magnetic pore
The Astrophysical Journal, 2015Co-Authors: S D T Grant, D B Jess, M G Moreels, R J Morton, D J Christian, Ioannis Giagkiozis, G Verth, V Fedun, P H Keys, T Van DoorsselaereAbstract:We present observational evidence of compressible magnetohydrodynamic Wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four Wavelength bands using the Dunn Solar Telescope. Employing Fourier and Wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181 412 s, with an average period 290 s, consistent with the global p -mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles of 6: 12 ◦ , 5: 82 ◦ and 15: 97 ◦ between 4170 u A continuum – G-band, G-band – Na I D1 and Na I D1 – Ca II K heights, respectively, reiterating the presence of upwardly-propagating sausage-mode Waves. A phase relationship of 0 ◦ between same-bandpass emission and area perturbations of the pore best categorises the Waves as belonging to the ‘slow’ regime of a dispersion diagram. Theoretical calculations reveal that the Waves are surface modes, with initial photospheric energies in excess of 35000 Wm 2 . The Wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport Waves that exhibit appreciable energy Damping, which may release considerable energy into the local chromospheric plasma. Subject headings: Magnetohydrodynamics (MHD) – Sun: Chromosphere – Sun: Oscillations – Sun: Photosphere
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Wave Damping observed in upwardly propagating sausage mode oscillations contained within a magnetic pore
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: S D T Grant, D B Jess, M G Moreels, R J Morton, D J Christian, Ioannis Giagkiozis, G Verth, V Fedun, P H Keys, T Van DoorsselaereAbstract:We present observational evidence of compressible magnetohydrodynamic Wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four Wavelength bands using the Dunn Solar Telescope. Employing Fourier and Wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181-412s, with an average period ~290s, consistent with the global p-mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out-of-phase with one another, displaying phase angles of 6.12 degrees, 5.82 degrees and 15.97 degrees between 4170 Angstrom continuum - G-band, G-band - Na I D1 and Na I D1 - Ca II K heights, respectively, reiterating the presence of upwardly-propagating sausage-mode Waves. A phase relationship of ~0 degrees between same-bandpass emission and area perturbations of the pore best categorises the Waves as belonging to the `slow' regime of a dispersion diagram. Theoretical calculations reveal that the Waves are surface modes, with initial photospheric energies in excess of 35000 W/m^2. The Wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport Waves that exhibit appreciable energy Damping, which may release considerable energy into the local chromospheric plasma.
B Hillebrands - One of the best experts on this subject based on the ideXlab platform.
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realization of a spin Wave switch based on the spin transfer torque effect
IEEE Magnetics Letters, 2018Co-Authors: Thomas J Meyer, B Hillebrands, Thomas Bracher, Frank Heussner, A A Serga, Hiroshi Naganuma, K Mukaiyama, Mikihiko Oogane, Yasuo Ando, Philipp PirroAbstract:We investigate the amplification of externally excited spin-Waves via the spin-transfer-torque (STT) effect in combination with the spin-Hall effect (SHE) resulting from short current pulses. In the case of overcompensation of the spin-Wave Damping, a strong nonlinear shift of the spin-Wave frequency spectrum occurs. In particular, this shift limits spin-Wave amplification from the SHE-STT effect. However, it allows for the realization of a spin-Wave switch. At the corresponding working point, efficient spin-Wave excitation is possible only in the presence of the SHE-STT effect with a spin-Wave intensity that is a factor of 20 larger than in the absence of the SHE-STT effect.
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realization of a spin Wave switch based on the spin transfer torque effect
arXiv: Mesoscale and Nanoscale Physics, 2018Co-Authors: Thomas J Meyer, B Hillebrands, Thomas Bracher, Frank Heussner, A A Serga, Hiroshi Naganuma, K Mukaiyama, Mikihiko Oogane, Yasuo Ando, Philipp PirroAbstract:We investigate the amplification of externally excited spin Waves via the Spin-Transfer-Torque (STT) effect in combination with the Spin-Hall-Effect (SHE) employing short current pulses. The results reveal that, in the case of an overcompensation of the spin Wave Damping, a strong nonlinear shift of the spin Wave frequency spectrum occurs. In particular, this shift affects the spin Wave amplification using the SHE-STT effect. In contrast, this effect allows for the realization of a spin Wave switch. By determining the corresponding working point, an efficient spin Wave excitation is only possible in the presence of the SHE-STT effect yielding an increased spin Wave intensity of a factor of 20 compared to the absence of the SHE-STT effect.
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characterization of spin transfer torque effect induced magnetization dynamics driven by short current pulses
Applied Physics Letters, 2018Co-Authors: Thomas J Meyer, B Hillebrands, Thomas Bracher, Frank Heussner, A A Serga, Hiroshi Naganuma, K Mukaiyama, Mikihiko Oogane, Yasuo Ando, Philipp PirroAbstract:We present a time-resolved study of the magnetization dynamics in a microstructured Cr|Heusler|Pt Waveguide driven by the spin-Hall-effect and the spin-transfer-torque effect via short current pulses. In particular, we focus on the determination of the threshold current at which the spin-Wave Damping is compensated. We have developed an alternative method based on the temporal evolution of the magnon density at the beginning of an applied current pulse at which the magnon density deviates from the thermal level. Since this method does not depend on the signal-to-noise ratio, it allows for a robust and reliable determination of the threshold current which is important for the characterization of any future application based on the spin-transfer-torque effect.
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characterization of spin transfer torque effect induced magnetization dynamics driven by short current pulses
arXiv: Mesoscale and Nanoscale Physics, 2017Co-Authors: Thomas J Meyer, B Hillebrands, Thomas Bracher, Frank Heussner, A A Serga, Hiroshi Naganuma, K Mukaiyama, Mikihiko Oogane, Yasuo Ando, Philipp PirroAbstract:We present a time-resolved study of the magnetization dynamics in a microstructured Cr$|$Heusler$|$Pt Waveguide driven by the Spin-Hall-Effect and the Spin-Transfer-Torque effect via short current pulses. In particular, we focus on the determination of the threshold current at which the spin-Wave Damping is compensated. We have developed a novel method based on the temporal evolution of the magnon density at the beginning of an applied current pulse at which the magnon density deviates from the thermal level. Since this method does not depend on the signal-to-noise ratio, it allows for a robust and reliable determination of the threshold current which is important for the characterization of any future application based on the Spin-Transfer-Torque effect.
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spin Wave versus joule heating in spin hall effect spin transfer torque driven cr heusler pt Waveguides
arXiv: Mesoscale and Nanoscale Physics, 2017Co-Authors: Thomas J Meyer, B Hillebrands, Thomas Bracher, Frank Heussner, A A Serga, Hiroshi Naganuma, K Mukaiyama, Mikihiko Oogane, Yasuo Ando, P PirroAbstract:We present a time-resolved study of the DC-current driven magnetization dynamics in a microstructured Cr/Heusler/Pt Waveguide by means of Brillouin light scattering. A reduction of the effective spin-Wave Damping via the spin-transfer-torque effect leads to a strong increase in the magnon density. This is accompanied by a decrease of the spin-Wave frequencies. By evaluating the time scales of these effects, the origin of this frequency shift can be identified. However, recently, we found that the experimental setup partially influences the decay of the spin-Wave intensity after the current pulse is switched off. Thus, further investigations on the presented effect are needed to allow for a more detailed analysis. For this reason, we need to withdraw the manuscript at this point and might publish an updated version later.
Heidi Nepf - One of the best experts on this subject based on the ideXlab platform.
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Wave Damping by flexible vegetation: Connecting individual blade dynamics to the meadow scale
Coastal Engineering, 2019Co-Authors: Heidi NepfAbstract:Abstract Aquatic vegetation provides ecosystem services of great value, including the Damping of Waves, which protects shorelines and reduces resuspension. This study proposes a physically-based model to predict the Wave decay associated with a submerged meadow as a function of plant morphology, flexibility, and shoot density. In particular, the study considers both the rigid (sheath) and flexible (blade) segments of the plant. Flexible plants reconfigure in response to Wave orbital velocity, which diminishes Wave decay relative to a rigid plant of the same morphology. The impact of reconfiguration on Wave decay can be characterized using an effective blade length, l e , which represents the length of a rigid blade that generates the same drag as the flexible blade of length l . The effective blade length depends on the Cauchy number, which defines the ratio of hydrodynamic drag to blade stiffness, and the ratio of blade length to Wave orbital excursion. This laboratory study considered how the scaling laws determined for individual blades can be used to predict the Wave decay over a meadow of multiple plants, each consisting of multiple blades attached at a rigid stem (sheath). First, the drag force on and motion of individual model blades (made of low-density polyethylene) was studied for a range of Wave conditions to provide empirical coefficients for the theoretically determined scaling laws for effective blade length, l e . Second, the effective blade length predicted for individual blades was incorporated into a meadow-scale model to predict Wave decay over a meadow. The meadow-scale model accounts for both the rigid and flexible parts of individual plants. Finally, Wave decay was measured over meadows of different plant density (shoots per bed area), and the measured decay was used to validate the Wave-decay model. Wave decay was shown to be similar over meadows with regular and random arrangements of plants.
G Venkat - One of the best experts on this subject based on the ideXlab platform.
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spin seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid state method
EPL, 2019Co-Authors: G Venkat, T A Rose, Christopher D W Cox, G B G Stenning, Andrew J Caruana, K MorrisonAbstract:We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets prepared by the solid-state method, where the choice of the sintering temperature can lead to mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate the saturation magnetization from magnetometry and to extract the spin Wave Damping α . The lowest Damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE) coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline samples for thermomagnetic applications.
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Spin Seebeck effect in polycrystalline yttrium iron garnet pellets prepared by the solid-state method [Letter]
2019Co-Authors: G Venkat, T A Rose, G B G Stenning, Andrew J Caruana, Chris Cox, K MorrisonAbstract:We study the properties of polycrystalline bulk yttrium iron garnet (YIG) pellets prepared by the solid-state method, where the choice of the sintering temperature can lead to mixed phases of yttrium iron perovskite (YIP) and YIG or single phase YIG. Magnetometry shows multiple switching regimes in the mixed-phase pellets where the saturation magnetization is dominated by the proportion of YIG present. Ferromagnetic resonance was used to corroborate the saturation magnetization from magnetometry and to extract the spin Wave Damping α. The lowest Damping was observed for the YIG pellet, which resulted in a spin Seebeck effect (SSE) coefficient that was approximately 55% of single crystal YIG. This demonstrates that macroscale crystallization does not play a major role in the SSE and paves the way for utilising polycrystalline samples for thermomagnetic applications
