18 results on '"Ostler, Thomas"'
Search Results
2. Simulations of magnetization reversal in FM/AFM bilayers with THz frequency pulses
- Author
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Hirst, Joel, Ruta, Sergiu, Jackson, Jerome, and Ostler, Thomas
- Published
- 2023
- Full Text
- View/download PDF
3. Three-dimensional topological magnetic monopoles and their interactions in a ferromagnetic meta-lattice
- Author
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Rana, Arjun, Liao, Chen-Ting, Iacocca, Ezio, Zou, Ji, Pham, Minh, Lu, Xingyuan, Subramanian, Emma-Elizabeth Cating, Lo, Yuan Hung, Ryan, Sinéad A., Bevis, Charles S., Karl, Jr, Robert M., Glaid, Andrew J., Rable, Jeffrey, Mahale, Pratibha, Hirst, Joel, Ostler, Thomas, Liu, William, O’Leary, Colum M., Yu, Young-Sang, Bustillo, Karen, Ohldag, Hendrik, Shapiro, David A., Yazdi, Sadegh, Mallouk, Thomas E., Osher, Stanley J., Kapteyn, Henry C., Crespi, Vincent H., Badding, John V., Tserkovnyak, Yaroslav, Murnane, Margaret M., and Miao, Jianwei
- Published
- 2023
- Full Text
- View/download PDF
4. Timescales and contribution of heating and helicity effect in helicity-dependent all-optical switching
- Author
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Li, Guan-Qi, Zheng, Xiang-Yu, Wang, Jun-Lin, Lu, Xian-Yang, Wu, Jing, Cai, Jian-Wang, Meng, Hao, Liu, Bo, Ostler, Thomas A., and Xu, Yong-Bing
- Published
- 2023
- Full Text
- View/download PDF
5. Computer simulations of ultrafast magnetisation reversal
- Author
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Ostler, Thomas Andrew and Chantrell, Roy
- Subjects
538 - Abstract
Magnetisation reversal is a process that is of paramount technological importance, as well as fascinating scientists in the field. Despite its importance, only recently have scientists begun to probe the limits of what can be achieved. Driven by consumer desire for compact devices using large scale storage, the size and time limit of magnetisation reversal have begun to be unravelled by exciting experiments using large scale national facilities and state of the art modelling. In the work presented here we develop a model of a ferrimagnetic material parameterised on experimental observations. The key magnetic features are shown to agree well with experimental measurements and provide a basis for more complex calculations. Using time and element resolved X-ray magnetic circular dichroism experiments, model calculations of laser induced magnetisation dynamics are compared to experimental measurements. We present results of switching on the sub-picosecond timescale and conclude that it is possible to reverse magnetisation using heat alone. The conclusion that magnetisation can be reversed without a directional stimulus is scientifically intriguing and never before predicted. Confirmation of such a reversal mechanism using heat alone is verified experimentally, comparing well with the model predictions.
- Published
- 2012
6. Optical receiver with helicity-dependent magnetization eversal
- Author
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Azim, Zubair Al, Ostler, Thomas, Xu, Chudong, and Roy, Kaushik
- Abstract
In this paper, we propose helicity-dependent switching (HDS) of magnetization in Co/Pt for an energy efficient optical receiver. Designing a low-power optical receiver for optical-to-electrical signal conversion has proven to be very challenging. Current day optical receivers use a photodiode that produces a photocurrent in response to input optical signals, and power hungry transimpedance amplifiers are required to amplify the small photocurrents. These limitations can be overcome by using light helicity-induced switching of magnetization which can avoid the requirement of photodiodes and subsequent transimpedance amplification by sensing the change in magnetization with a magnetic tunnel junction (MTJ). Magnetization switching of a thin ferromagnet layer using circularly polarized laser pulses has recently been demonstrated which shows a one-to-one correspondence between light helicity and the magnetization state. We use these phenomena to directly switch the magnetization state of a thin Co/Pt ferromagnet layer at the receiver via circularly polarized laser pulses. The circular polarization is controlled in accordance with digital input data which establishes a one-to-one correspondence between the transmitted data and output magnetization state. The Co/Pt layer is used as the free layer of an MTJ, the resistance of which is modified by the laser pulses. Since the output magnetization state is controlled by the input data, the MTJ resistance is directly converted to a digital output signal. Our device-to-circuit level simulation results indicate that HDS-based optical receiver circuit consumes only 0.124 pJ/bit energy, which is much lower than existing techniques.
- Published
- 2019
7. Roles of heating and helicity in ultrafast all-optical magnetization switching in TbFeCo
- Author
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Lu, Xianyang, Zou, Xiao, Hinzke, Denize, Wang, Yichuan, Cheng, Tuyuan, Wu, Jing, Ostler, Thomas Andrew, Cai, Jianwang, Nowak, Ulrich, Chantrell, Roy William, Zhai, Ya, and Xu, Yongbing
- Abstract
Using the time-resolved magneto-optical Kerr effect method, helicity-dependent all-optical magnetization switching (HD-AOS) is observed in ferrimagnetic TbFeCo films. Our results reveal the individual roles of the thermal and nonthermal effects after a single circularly polarized laser pulse. The evolution of this ultrafast switching occurs over different time scales, and a defined magnetization reversal time of 460 fs is shown—the fastest ever observed. Micromagnetic simulations based on a single macro-spin model, taking into account both heating and the inverse Faraday effect, are performed which reproduce HD-AOS demonstrating a linear path for magnetization reversal.
- Published
- 2018
8. Substrate Induced Strain Field in FeRh Epilayers Grown on Single Crystal MgO (001) Substrates
- Author
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Barton, C. W., Ostler, Thomas, Huskisson, D., Kinane, C. J., Haigh, S. J., Hrkac, G., and Thomson, T
- Abstract
Equi-atomic FeRh is highly unusual in that it undergoes a first order meta-magnetic phase transition from an antiferromagnet to a ferromagnet above room temperature (Tr ≈ 370 K). This behavior opens new possibilities for creating multifunctional magnetic and spintronic devices which can utilise both thermal and applied field energy to change state and functionalise composites. A key requirement in realising multifunctional devices is the need to understand and control the properties of FeRh in the extreme thin film limit (tFeRh
- Published
- 2017
9. Soft x-ray vector ptycho-tomography: a new quantitative vector nanoimaging method for spin textures in 3D.
- Author
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Liao, Chen-Ting, Rana, Arjun, Iacocca, Ezio, Zou, Ji, Pham, Minh, Lu, Xingyuan, Cating Subramanian, Emma-Elizabeth, Lo, Yuan Hung, Ryan, Sinéad A., Bevis, Charles S., Karl, Robert M., Glaid, Andrew J., Rable, Jeffrey, Mahale, Pratibha, Hirst, Joel, Ostler, Thomas, Liu, William, O'Leary, Colum M., Yu, Young-Sang, and Bustillo, Karen
- Published
- 2023
- Full Text
- View/download PDF
10. Optical Receiver With Helicity-Dependent Magnetization Reversal.
- Author
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Azim, Zubair Al, Ostler, Thomas A., Xu, Chudong, and Roy, Kaushik
- Subjects
- *
MAGNETIZATION , *ELECTROMAGNETIC induction , *MAGNETOCALORIC effects , *HELICITY of nuclear particles , *MAGNETIC tunnelling - Abstract
In this paper, we propose helicity-dependent switching (HDS) of magnetization in Co/Pt for an energy efficient optical receiver. Designing a low-power optical receiver for optical-to-electrical signal conversion has proven to be very challenging. Current day optical receivers use a photodiode that produces a photocurrent in response to input optical signals, and power hungry transimpedance amplifiers are required to amplify the small photocurrents. These limitations can be overcome by using light helicity-induced switching of magnetization which can avoid the requirement of photodiodes and subsequent transimpedance amplification by sensing the change in magnetization with a magnetic tunnel junction (MTJ). Magnetization switching of a thin ferromagnet layer using circularly polarized laser pulses has recently been demonstrated which shows a one-to-one correspondence between light helicity and the magnetization state. We use these phenomena to directly switch the magnetization state of a thin Co/Pt ferromagnet layer at the receiver via circularly polarized laser pulses. The circular polarization is controlled in accordance with digital input data which establishes a one-to-one correspondence between the transmitted data and output magnetization state. The Co/Pt layer is used as the free layer of an MTJ, the resistance of which is modified by the laser pulses. Since the output magnetization state is controlled by the input data, the MTJ resistance is directly converted to a digital output signal. Our device-to-circuit level simulation results indicate that HDS-based optical receiver circuit consumes only 0.124 pJ/bit energy, which is much lower than existing techniques. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
11. Ultrafast thermally induced magnetic switching in synthetic ferrimagnets.
- Author
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Evans, Richard F. L., Ostler, Thomas A., Chantrell, Roy W., Radu, Ilie, and Rasing, Theo
- Subjects
- *
MAGNETIC control , *FERRIMAGNETIC materials , *MAGNETIC structure , *MAGNETIC moments , *OPTICAL switching , *ULTRASHORT laser pulses , *MAGNETIZATION - Abstract
Synthetic ferrimagnets are composite magnetic structures formed from two or more anti-ferromagnetically coupled magnetic sublattices with different magnetic moments. Here, we report on atomistic spin simulations of the laser-induced magnetization dynamics on such synthetic ferrimagnets and demonstrate that the application of ultrashort laser pulses leads to sub-picosecond magnetization dynamics and all-optical switching in a similar manner as in ferrimagnetic alloys. Moreover, we present the essential material properties for successful laser-induced switching, demonstrating the feasibility of using a synthetic ferrimagnet as a high density magnetic storage element without the need of a write field. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
12. Crystallographically amorphous ferrimagnetic alloys: Comparing a tocaliied atornisik spin model with experiments.
- Author
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Ostler, Thomas A., Evans, Richard F. L., Chantrell, Roy W., Atxitia, Unai, Chubykalo-Fesenko, Oksana, Radu, Ilie, Abrudan, Radu, Radu, Florin, Tsukamoto, Arata, Itoh, A., Kirilyuk, Andrei, Rasing, Theo, and Kimel, Alexey
- Subjects
- *
FERROMAGNETISM , *MAGNETOOPTICS , *CIRCULAR dichroism , *PARAMAGNETISM , *MAGNETIZATION - Abstract
We present a computational model of crystallographically amorphous ferrimagnetic alloys using a stochastic Landau-Lifshitz-Gilbert equation of motion for atomistic spins and an atomistic spin Hamiltonian with Heisenberg exchange. The spontaneous equilibrium magnetization is calculated and a comparison with a mean field model is made. The simulations show excellent agreement with experiments on GdFeCo using x-ray magnetic circular dichroism to determine the individual sublattice magnetizations. The calculated temperature dependence of the magnetization shows a polarization of the Gd sublattice leading to a common Curie temperature, in agreement with the experimental data. The intersublattice exchange is shown to be an important energy transfer channel for ultrafast dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
13. Laser Induced Magnetization Reversal for Detection in Optical Interconnects.
- Author
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Azim, Zubair Al, Fong, Xuanyao, Ostler, Thomas, Chantrell, Roy, and Roy, Kaushik
- Subjects
MAGNETIZATION reversal ,OPTICAL interconnects ,INTEGRATED circuit interconnections ,MAGNETIC tunnelling ,ENERGY consumption ,FEMTOSECOND lasers - Abstract
Optical interconnect has emerged as the front-runner to replace electrical interconnect especially for off-chip communication. However, a major drawback with optical interconnects is the need for photodetectors and amplifiers at the receiver, implemented usually by direct bandgap semiconductors and analog CMOS circuits, leading to large energy consumption and slow operating time. In this letter, we propose a new optical interconnect architecture that uses a magnetic tunnel junction (MTJ) at the receiver side that is switched by femtosecond laser pulses. The state of the MTJ can be sensed using simple digital CMOS latches, resulting in significant improvement in energy consumption. Moreover, magnetization in the MTJ can be switched on the picoseconds time-scale and our design can operate at a speed of 5 Gb/s for a single link. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
14. Modeling the thickness dependence of the magnetic phase transition temperature in thin FeRh films.
- Author
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Ostler, Thomas Andrew, Barton, Craig, Thomson, Thomas, and Hrkac, Gino
- Subjects
- *
MAGNETIC transitions , *TEMPERATURE , *MAGNESIUM oxide - Abstract
FeRh and its first-order phase transition can open new routes for magnetic hybrid materials and devices under the assumption that it can be exploited in ultra-thin-film structures. Motivated by experimental measurements showing an unexpected increase in the phase transition temperature with decreasing thickness of FeRh on top of MgO, we develop a computational model to investigate strain effects of FeRh in such magnetic structures. Our theoretical results show that the presence of the MgO interface results in a strain that changes the magnetic configuration which drives the anomalous behavior. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
15. Effects of interactions on the relaxation processes in magnetic nanostructures.
- Author
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Atkinson, Lewis J., Ostler, Thomas A., Hovorka, O., Wang, K. K., Lu, B., Ju, G. P., Hohlfeld, J., Bergman, B., Koopmans, B., and Chantrell, Roy W.
- Subjects
- *
MAGNETIC nanoparticles , *MAGNETIC storage , *OPTICAL resonance , *MAGNETIC relaxation , *MAGNETOSTATICS - Abstract
Controlling the relaxation of magnetization in magnetic nanostructures is key to optimizing magnetic storage device performance. This relaxation is governed by both intrinsic and extrinsic relaxation mechanisms and with the latter strongly dependent on the interactions between the nanostructures. In the present work we investigate laser induced magnetization dynamics in a broadband optical resonance type experiment revealing the role of interactions between nanostructures on the relaxation processes of granular magnetic structures. The results are corroborated by constructing a temperature dependent numerical micromagnetic model of magnetization dynamics based on the Landau-Lifshitz-Bloch equation. The model predicts a strong dependence of damping on the key material properties of coupled granular nanostructures in good agreement with the experimental data. We show that the intergranular, magnetostatic and exchange interactions provide a large extrinsic contribution to the damping. Finally we show that the mechanism can be attributed to an increase in spin-wave degeneracy with the ferromagnetic resonance mode as revealed by semianalytical spin-wave calculations. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
16. Local thermoelectric response from a single Ne'el domain wall.
- Author
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Puttock, Robert, Barton, Craig, Saugar, Elias, Klapetek, Petr, Fernández-Scarioni, Alexander, Freitas, Paulo, Schumacher, Hans W., Ostler, Thomas, Chubykalo-Fesenko, Oksana, and Kazakova, Olga
- Subjects
- *
CONDENSED matter physics , *NERNST effect , *NANOWIRES - Abstract
The article presents a analysis of the thermoelectric response from a single trapped domain wall with the use of a heated scanning probe. Topics discussed include the importance of resolving the nanoscale magnetization in addressing the underconstrained problem of determining the spin texture, symmetry of magnetothermoelectric effects, and the key features of the scanning thermoelectric microscopy technique.
- Published
- 2022
- Full Text
- View/download PDF
17. A multiscale model of the efect of Ir thickness on the static and dynamic properties of Fe/Ir/Fe flms
- Author
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Thomas Ostler, Roy W. Chantrell, László Szunyogh, Gino Hrkac, László Oroszlány, Ramón Cuadrado, Vienna Science and Technology Fund, Engineering and Physical Sciences Research Council (UK), Royal Society (UK), European Commission, Université de Liège, Hungarian Scientific Research Fund, Ministerio de Economía y Competitividad (España), Hungarian Academy of Sciences, National Research, Development and Innovation Office (Hungary), Chantrell, Roy W., Ostler, Thomas A., Chantrell, Roy W. [0000-0001-5410-5615], and Ostler, Thomas A. [0000-0002-1328-1839]
- Subjects
Materials science ,media_common.quotation_subject ,lcsh:Medicine ,Frustration ,02 engineering and technology ,01 natural sciences ,Article ,Magnetization ,Surfaces, interfaces and thin films ,Magnetic properties and materials ,0103 physical sciences ,medicine ,lcsh:Science ,010306 general physics ,Softening ,media_common ,Multidisciplinary ,Condensed matter physics ,Magnon ,lcsh:R ,Demagnetizing field ,Stiffness ,021001 nanoscience & nanotechnology ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,medicine.symptom ,0210 nano-technology ,Dispersion (chemistry) ,Ultrashort pulse - Abstract
The complex magnetic properties of Fe/Ir/Fe sandwiches are studied using a hierarchical multi-scale model. The approach uses first principles calculations and thermodynamic models to reveal the equilibrium spinwave, magnetization and dynamic demagnetisation properties. Finite temperature calculations show a complex spinwave dispersion and an initially counter-intuitive, increasing exchange stiffness with temperature (a key quantity for device applications) due to the effects of frustration at the interface, which then decreases due to magnon softening. Finally, the demagnetisation process in these structures is shown to be much slower at the interface as compared with the bulk, a key insight to interpret ultrafast laser-induced demagnetization processes in layered or interface materials., Gino Hrkac (GH) acknowledges support from the Vienna Science and Technology Fund (WWTF) under Grant No. MA14-44, through the EPSRC Grant No. EP/K008412/1, and from the Royal Society under Grant No. UF080837. Thomas A Ostler (TAO) gratefully acknowledges the support of the Marie Curie incoming BeIPD-COFUND fellowship program at the University of Liège. Ramon Cuadrado (RC) acknowledges the funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodoswa-Curie grant agreement No. 665919. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2013-0295). László Oroszlány (LO) and László Szunyogh (LS) are grateful for the support by the Hungarian National Scientific Research Fund (NKFIH) under project Nos. K115575, K108676, K115608 and FK124723. L. O. also acknowledges support from the Janos Bolyai Scholarship of the Hungarian Academy of Sciences as well as the National Quantum Technologies Program 2017-1.2.1-NKP-2017-00001 of the NRDI Office of Hungary. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 737093, FEMTOTERABYTE as well as the financial support of the Advanced Storage Technology Consortium and Seagate Technology.
- Published
- 2018
18. A multiscale model of the effect of Ir thickness on the static and dynamic properties of Fe/Ir/Fe films.
- Author
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Cuadrado R, Oroszlány L, Szunyogh L, Hrkac G, Chantrell RW, and Ostler TA
- Abstract
The complex magnetic properties of Fe/Ir/Fe sandwiches are studied using a hierarchical multi-scale model. The approach uses first principles calculations and thermodynamic models to reveal the equilibrium spinwave, magnetization and dynamic demagnetisation properties. Finite temperature calculations show a complex spinwave dispersion and an initially counter-intuitive, increasing exchange stiffness with temperature (a key quantity for device applications) due to the effects of frustration at the interface, which then decreases due to magnon softening. Finally, the demagnetisation process in these structures is shown to be much slower at the interface as compared with the bulk, a key insight to interpret ultrafast laser-induced demagnetization processes in layered or interface materials.
- Published
- 2018
- Full Text
- View/download PDF
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