6 research outputs found
Accessing ultrafast spin-transport dynamics in copper using broadband terahertz spectroscopy
We study the spatiotemporal dynamics of ultrafast electron spin transport
across nanometer-thick copper layers using broadband terahertz spectroscopy.
Our analysis of temporal delays, broadening and attenuation of the spin-current
pulse revealed ballistic-like propagation of the pulse peak, approaching the
Fermi velocity, and diffusive features including a significant velocity
dispersion. A comparison to the frequency-dependent Ficks law identified the
diffusion-dominated transport regime for distances larger than 2 nm. The
findings lie the groundwork for designing future broadband spintronic devices.Comment: Main text consists of 3 figures and 4 pages of tex
Terahertz probing of anisotropic conductivity and morphology of CuMnAs epitaxial thin films
Antiferromagnetic CuMnAs thin films have attracted attention since the
discovery of the manipulation of their magnetic structure via electrical,
optical, and terahertz pulses of electric fields, enabling convenient
approaches to the switching between magnetoresistive states of the film for the
information storage. However, the magnetic structure and, thus, the efficiency
of the manipulation can be affected by the film morphology and growth defects.
In this study, we investigate the properties of CuMnAs thin films by probing
the defect-related uniaxial anisotropy of electric conductivity by contact-free
terahertz transmission spectroscopy. We show that the terahertz measurements
conveniently detect the conductivity anisotropy, that are consistent with
conventional DC Hall-bar measurements. Moreover, the terahertz technique allows
for considerably finer determination of anisotropy axes and it is less
sensitive to the local film degradation. Thanks to the averaging over a large
detection area, the THz probing also allows for an analysis of strongly
non-uniform thin films. Using scanning near-field terahertz and electron
microscopies, we relate the observed anisotropic conductivity of CuMnAs to the
elongation and orientation of growth defects, which influence the local
microscopic conductivity. We also demonstrate control over the morphology of
defects by using vicinal substrates.Comment: 33 pages, 16 figure
Study of spintronic phenomena in magnetically ordered stuctures using terahertz spectroscopy
The main objective of this thesis was to bring the first experimental evidence about the spin-Hall magnetoresistance (SMR) in the Terahertz (THz) spectral range. The time-domain THz spectroscopy (TDTS) was chosen as the main method, and we presented a new experimental scheme, which allows us to observe SMR or magnetoresistive effects with similar symmetry at a wide range of THz frequencies very efficiently. We focused on the study of SMR in the bilayers consisting of either a prototypical ferrimagnetic isolator or of heavy metal (FI/HM) and metallic stacks of ferromagnetic CoFeB and heavy metal Pt layer (FM/HM). While SMR shows a rapid decrease already at the lowest THz frequencies (< 1 THz) in the FI/HM structures, the SMR in FM/HM bilayers persists above 30 THz. These observations are then explained by a different mechanism of SMR. The second part of the thesis is devoted to the construction of the new TDTS setup and an easy-to-use model of the THz setup using the Gaussian description of THz radiation. The simulated results have been compared to corresponding experimental measurements using a spintronic THz emitter (STE). The last part of the thesis describes the emission of intensive THz pulses from large-area STE
Studium spintronických jevů v magneticky uspořádaných strukturách pomocí terahertzové spektroskopie
Hlavným cieľom tejto práce bolo priniesť prvý experimentálny dôkaz o existencií spin-Hall magnetorezistencie (SMR) v Terahertzovej (THz) spektrálnej oblasti. Ako hlavnú metódu sme zvolili časovo-rozlíšenú THz spektroskopiu (TDTS) a prezentovali sme experimentálne usporiadanie, ktoré umožňuje pozorovať efektívne SMR alebo iné magnetorezistívne javy s podobnou symetriou v širokom rozsahu THz frekvencií. V rámci tejto práce sme sa zamerali na štúdium dvojvrstiev ferimagnetického izolátoru a ťažkého kovu (FI/HM) a kovových dvojvrstiev feromagnetu CoFeB a ťažkého kovu Pt (FM/HM). Zatiaľ čo SMR v FI/HM štruktúre vykazuje výrazný pokles už v nízkych THz frekvenciách (<1 THz), SMR v dvojvrstvách FM/HM pretrváva aj nad 30 THz. Tieto výsledky sú nasledovne vysvetlené rozdielnymi mechanizmami SMR. Druhá časť tejto práce sa zaoberá konštrukciou nového TDTS experimentálneho usporiadania a jednoduchým modelom THz experimentálneho usporiadania pomocou Gaussovských zväzkov THz žiarenia. Výsledky simulácií boli následne porovnané s príslušnými experimentálnymi meraniami pomocou spintronického THz emitoru (STE). Posledná časť sa venuje popisu intenzívnym laserových pulzov z plošných STE.The main objective of this thesis was to bring the first experimental evidence about the spin-Hall magnetoresistance (SMR) in the Terahertz (THz) spectral range. The time-domain THz spectroscopy (TDTS) was chosen as the main method, and we presented a new experimental scheme, which allows us to observe SMR or magnetoresistive effects with similar symmetry at a wide range of THz frequencies very efficiently. We focused on the study of SMR in the bilayers consisting of either a prototypical ferrimagnetic isolator or of heavy metal (FI/HM) and metallic stacks of ferromagnetic CoFeB and heavy metal Pt layer (FM/HM). While SMR shows a rapid decrease already at the lowest THz frequencies (< 1 THz) in the FI/HM structures, the SMR in FM/HM bilayers persists above 30 THz. These observations are then explained by a different mechanism of SMR. The second part of the thesis is devoted to the construction of the new TDTS setup and an easy-to-use model of the THz setup using the Gaussian description of THz radiation. The simulated results have been compared to corresponding experimental measurements using a spintronic THz emitter (STE). The last part of the thesis describes the emission of intensive THz pulses from large-area STE.Department of Chemical Physics and OpticsKatedra chemické fyziky a optikyMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Magneto-optical study of antiferromagnetic materials for spintronics
The main goal of this thesis was to develop an experimental technique for investigation of ferromagnetic and antiferromagnetic materials using magneto-optical effects that are quadratic in magnetization. Using a prototype of 2-dimensional electromagnet, which enables to rotate magnetic field of constant magnitude in the sample plane, we were able to study spectral dependences and anisotropies of corresponding magneto-optical coefficients. In ferromagnetic semiconductor GaMnAs we revealed that the anisotropy of Voigt effect magneto-optical coefficient is strongly wavelength dependent - this coefficient can be both isotropic and anisotropic. Very strong anisotropy of this coefficient was observed for metallic FeRh in a ferromagnetic state. Finally, a new method that can be used to measure Voigt effect in antiferromagnetic state of FeRh was demonstrated
Magneto-optické studium antiferomagnetických materiálů pro spintroniku
The main goal of this thesis was to develop an experimental technique for investigation of ferromagnetic and antiferromagnetic materials using magneto-optical effects that are quadratic in magnetization. Using a prototype of 2-dimensional electromagnet, which enables to rotate magnetic field of constant magnitude in the sample plane, we were able to study spectral dependences and anisotropies of corresponding magneto-optical coefficients. In ferromagnetic semiconductor GaMnAs we revealed that the anisotropy of Voigt effect magneto-optical coefficient is strongly wavelength dependent - this coefficient can be both isotropic and anisotropic. Very strong anisotropy of this coefficient was observed for metallic FeRh in a ferromagnetic state. Finally, a new method that can be used to measure Voigt effect in antiferromagnetic state of FeRh was demonstrated.Hlavným cieľom tejto práce bolo vyvinúť experimentálnu techniku na štúdium feromagnetických a antiferomagnetických materiálov využitím magneto-optických javov kvadratických v magnetizácií. Využitím prototypu 2-dimenzionálneho elektromagnetu, ktorý umožňuje točiť magnetickým poľom konštantnej veľkosti v rovine vzorku, sme boli schoppný študovať spektrálnu závislosť a anizotropiu príslušných magneto-optických koeficientov. Vo feromagnetickom polovodiči GaMnAs sme zistili, že anizotropia koeficientu Voigtovho javu je silne závislá na vlnovej dĺžke - tento koeficient môže byť izotropný aj anizotropný. Veľmi silná anizotropia tohto koeficientu bola pozorovaná pre kov FeRh vo feromagnetickom stave. Na záver bola demonštrovaná nová metóda, ktorá umožňuje merať Voigtov jav v antiferomagnetickom stave FeRh.Katedra chemické fyziky a optikyDepartment of Chemical Physics and OpticsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic