| 1. |
- Čiučiulkaitė, Agnė, MSc, 1991-
(författare)
-
Dynamics in magnetic metamaterials
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metamaterials are artificially created structures with properties that are not found in nature. They can be tailored to achieve desired response to external excitations such as external electric and magnetic fields, as well as to enhance materials’ optical or magnetic activity. Magnetic metamaterials comprised of arrays of sub-micrometer sized magnetic elements, can be used for a range of different applications, such as magnonic crystals and building blocks for magnetic memory elements.In this work, pathways for tuning magnetization dynamics are explored. Different magnetic metamaterials containing arrays of sub-micrometer sized elements, refered to as nanomagnets, were used as model systems for these explorations. The nano-magnets comrising these arrays are of two kinds: XY-rotors, with a magnetization direction rotating freely in-plane of a disk, and Ising-like spins, pointing along either of the two allowed magnetization directions. The Ising-like spins can be realized in either in-plane or out-of-plane magnetized materials.Collective magnetization dynamics were investigated in square arrays of coupled nanomagnets. Studies revealed that nanomagnet’s magnetization state cannot always be approximated by a ridig mesospin approximation. Instead, it was demonstrated that upon an external perturbation, such as an external magnetic or thermal field, internal magnetization experience texture excitations. The observed texture excitations have implications on the nanomagnet coupling in an array.Arrays, where collective phenomena emerge via excited plasmon resonances, were used for investigations of light-induced dynamics processes. Studies revealed importance of an array design for the observation of magneto-optical activity enhancement and more eÿcient ultrafast magnetization dynamics. It was reported that in arrays containing truncated Au nanocones with TbCo tip, enhancement of TbCo demagnetization can be achieved via resonant light illumination.Utilizing the array concept and magnetic anisotropy of a material, it is possible to create metamaterials, where a range of magnetization dynamics regimes can be investigated. Inter-element spacing defines on which lengthscale the nanomagnets will be coupled and which effects can be utilized for tuning system’s magneto-optical response and excited magnetization dynamics.
|
|
| 2. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
-
Impact of the magnetic layer crystal growth optimization on the THzemission from spintronic Fe/Pt emitters
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate the THz emission characteristics of ferromagnetic/non-magnetic metallic heterostructures, focusing on thin Fe/Pt bilayers. In particular, we report on the impact of optimized crystal growth of the epitaxial Fe layers on the THz emission amplitude and spectral bandwidth. We demonstrate a 5 % enhancement of the emitted intensity, related to reduced spin scattering and higher interface transmission. Our work provides a pathway for devicing optimal spintronic THz emitters based on epitaxial Fe. It also highlights how THz emission measurements can be utilized to characterize the changes in out-of-equilibrium spin current dynamics in metallic heterostructures, driven by subtle structural refinement.
|
|
| 3. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
-
Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys
- 2020
-
Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 4:10
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous TbxCo100-x magnetic alloys exhibit a list of intriguing properties, such as perpendicular magnetic anisotropy, high magneto-optical activity, and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field, and the performance of light-induced magnetization switching. In this paper, we investigate the magnetic, optical, and magneto-optical properties of various TbxCo100-x thin-film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of TbxCo100-x layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at. %, helicity-dependent all-optical switching of magnetization can be achieved, albeit in a multishot framework. We explain this property to arise from the helicity-dependent laser-induced magnetization on the Co sublattice due to the inverse Faraday effect. Our paper provides an insight into material aspects for future potential hybrid magnetoplasmonic TbCo-based architectures.
|
|
| 4. |
- Ciuciulkaite, Agne, MSc, 1991-
(författare)
-
The interaction of light and magnetism in the TbxCo100-x system
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development of the faster and denser magnetic memory storage elements has been an active area of research since early 20th century. The path of research on magnetization manipulation began with firstly changing the magnetization state of a medium in an external magnetic field, then heating of a medium and magnetizing with a permanent magnet was explored, while the latest efforts have been focused on switching the magnetization only by a polarized laser light. Nowadays due to the technological advancement of lasers and material fabrication methods, the search and development process of magnetic memory elements is much faster. The implementation of such technologies, however, relies on finding suitable magnetic materials which would allow for a fast magnetization writing and read-out processes and would remain magnetized, even with the reduced dimensions. Ferrimagnetic rare Earth - transition metal (RE-TM) alloys have been used for fabricating magneto-optical recording media already since the 1990’s. Relatively recently, in 2007, it was demonstrated that the ferrimagnetic GdFeCo alloy magnetization state can be switched using only circularly polarized laser light. Hence, ferrimagnetic RE-TMalloys could be suitable candidates for all-optical light-induced magnetization switching (AOS), without any external magnetic field. Another combination of RE-TM alloys that was shown to exhibit AOS is ferrimagnetic amorphous alloys containing terbium and cobalt (Tb:Co). They have attracted attention due to their strong out-of-plane magnetic anisotropy, high magneto-optical activity and amorphicity, which makes them attractive from a fabrication point of view since a variety of substrates and buffer layers could be used for growing such layers. In this Thesis, TbCo alloys are investigated in order to examine how the magnetic, optical and magneto-optical properties could be tuned by varying the elemental ratio and film thickness. The main question that was addressed here was whether such a system is suitable for fabrication of nanosized magnetic elements as the building blocks for the magnetic memory applications. TbCo alloys were prepared as thin films by magnetron co-sputtering method onto different substrates and buffer layers. Films were characterized using a variety of techniques such as an ion beam analysis, an x-ray reflectivity and diffraction, and magneto-optical characterization techniques. It was observed that the properties of such alloys depend not only on the Tb:Co ratio but also on the film thickness and an underlying buffer layer. Magnetization compensation point, at which the magnetization of a film is zero, as in an antiferromagnet, can be modified depending on the buffer layer. All-optical switching (AOS) of magnetization experiments were performed on the fabricated samples. It was determined that AOS with at least 50-100 laserpulses can be achieved for the films grown directly onto fused silica substrates and with the compositions above the magnetization compensation point at room temperature, in the range of 24 - 30 at.% Tb. In the Outlook, the initial efforts of patterning the films into the arrays of nanosized elements are presented. It is demonstrated that after the lithographic patterning of the films, the resulting nanosized elements remained out-of-plane magnetized. In this work it is shown that the ferrimagnetic TbCo alloy system is a potential candidate material for bothfacilitating AOS and the fabrication of arrays of nanomagnets. Combining the TbCo alloys,which show AOS, together with a suitable buffer layer and patterning the hybrid structure,could enable selective element-by-element magnetization switching for the magnetic memorystorage devices.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Mishra, K., et al.
(författare)
-
Ultrafast Demagnetization Control in Magnetophotonic Surface Crystals
- 2022
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 22:23, s. 9773-80
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic memory combining plasmonics and magnetism is poised to dramatically increase the bit density and energy efficiency of light-assisted ultrafast magnetic storage, thanks to nanoplasmon-driven enhancement and confinement of light. Here we devise a new path for that, simultaneously enabling light driven bit downscaling, reduction of the required energy for magnetic memory writing, and a subtle control over the degree of demagnetization in a magnetophotonic surface crystal. It features a regular array of truncated-nanocone-shaped Au-TbCo antennas showing both localized plasmon and surface lattice resonance modes. The ultrafast magnetization dynamics of the nanoantennas show a 3-fold resonant enhancement of the demagnetization efficiency. The degree of demagnetization is further tuned by activating surface lattice modes. This reveals a platform where ultrafast demagnetization is localized at the nanoscale and its extent can be controlled at will, rendering it multistate and potentially opening up so-far-unforeseen nanomagnetic neuromorphic-like systems operating at femtosecond time scales controlled by light.
|
|
| 8. |
|
|
| 9. |
- Mishra, K., et al.
(författare)
-
Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling
- 2021
-
Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:46, s. 19367-19375
-
Tidskriftsartikel (refereegranskat)abstract
- The quest to improve the density, speed and energy efficiency of magnetic memory storage has led to the exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus the potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy funneling through plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such a substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the resonant optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This observation is an important step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.
|
|
| 10. |
- Pohlit, Merlin, et al.
(författare)
-
Collective magnetic dynamics in artificial spin ice probed by ac susceptibility
- 2020
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:13
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the study of the thermal dynamics of square artificial spin ice, probed by means of temperatureand frequency-dependent ac susceptibility. Pronounced influence of the interisland coupling strength was found on the frequency response of the samples. Through the subsequent analysis of the frequency- and coupling-dependent freezing temperatures, we discuss the phenomenological parameters obtained in the framework of the Vogel-Fulcher-Tammann law in terms of the samples' microscopic features. The high sensitivity and robust signal to noise ratio of ac susceptibility validate the latter as a promising and simple experimental technique for resolving the dynamics and temperature driven dynamics crossovers for the case of artificial spin ice.
|
|
