Kohärente Spinphänomene in Festkörpern
Permanent URI for this collection
Browse
Recent Submissions
Item Modulation of the transient magnetization of an EuO/Co bilayer tuned by optical excitation(2023-07-14) Mönkebüscher, David; Rosenberger, Paul; Mertens, Fabian; Adam, Roman; Schneider, Claus M.; Parlak, Umut; Müller, Martina; Cinchetti, MirkoThe magnetic proximity effect provides a promising way to increase the low Curie temperature (TC) of europium monoxide (EuO) toward or even above room temperature, while keeping its stoichiometry and insulating properties. This work studies EuO/Co bilayers using static and time-resolved magneto-optical Kerr effect measurements, and explores the influence of magnetic proximity on TC and on the spin dynamics in EuO. Excitation above the EuO bandgap results in an ultrafast enhancement of the EuO magnetization followed by a demagnetization within nanoseconds. This behaviour is also visible upon selectively photoexciting Co in the EuO/Co bilayer placed in an out-of-plane magnetic field, which is attributed to propagation of a superdiffusive spin current from Co into EuO. As the spin dynamics of Co shows a transient thermal demagnetization, the bilayer provides a system where the transient magneto-optical signal can be tuned in amplitude and sign by varying external parameters such as the sample temperature or pump fluence. Moreover, in a strong excitation regime it is possible to measure the magnetic hysteresis of the underlying EuO, which is present up to room temperature – giving experimental evidence for the presence of a tuneable magnetic proximity coupling between Co and EuO.Item Enhancing electron correlation at a 3d ferromagnetic surface(2022-10-27) Janas, David Maximilian; Droghetti, Andrea; Ponzoni, Stefano; Cojocariu, Iulia; Jugovac, Matteo; Feyer, Vitaliy; Radonjić, Miloš M.; Rungger, Ivan; Chioncel, Liviu; Zamborlini, Giovanni; Cinchetti, MirkoSpin-resolved momentum microscopy and theoretical calculations are combined beyond the one-electron approximation to unveil the spin-dependent electronic structure of the interface formed between iron (Fe) and an ordered oxygen (O) atomic layer, and an adsorbate-induced enhancement of electronic correlations is found. It is demonstrated that this enhancement is responsible for a drastic narrowing of the Fe d-bands close to the Fermi energy (EF) and a reduction of the exchange splitting, which is not accounted for in the Stoner picture of ferromagnetism. In addition, correlation leads to a significant spin-dependent broadening of the electronic bands at higher binding energies and their merging with satellite features, which are manifestations of a pure many-electron behavior. Overall, adatom adsorption can be used to vary the material parameters of transition metal surfaces to access different intermediate electronic correlated regimes, which will otherwise not be accessible. The results show that the concepts developed to understand the physics and chemistry of adsorbate–metal interfaces, relevant for a variety of research areas, from spintronics to catalysis, need to be reconsidered with many-particle effects being of utmost importance. These may affect chemisorption energy, spin transport, magnetic order, and even play a key role in the emergence of ferromagnetism at interfaces between non-magnetic systems.Item Ultrafast coherent THz lattice dynamics coupled to spins in the van der Waals antiferromagnet FePS3(2022-12-21) Mertens, Fabian; Mönkebüscher, David; Parlak, Umut; Boix-Constant, Carla; Mañas-Valero, Samuel; Matzer, Margherita; Adhikari, Rajdeep; Bonanni, Alberta; Coronado, Eugenio; Kalashnikova, Alexandra M.; Bossini, Davide; Cinchetti, MirkoCoherent THz optical lattice and hybridized phonon–magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS3. The laser-driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which is utilized to excite the hybridized phonon–magnon mode optically. These findings open a pathway toward the optical control of coherent THz photo–magnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the 2D limit.Item Phononkopplung an Spins und Ladungen auf der ultraschnellen Zeitskala im antiferromagnetischen Halbleiter MnTe(2022) Terschanski, Marc; Cinchetti, Mirko; Akimov, IlyaIm ersten Teil dieser Arbeit wird ein neu installierter Aufbau beschrieben, der die gleichzeitige Durchführung optischer und magneto-optischer Pump-Probe Experimente als Funktion der Temperatur, eines Magnetfeldes oder eines angelegten elektrischen Feldes ermöglicht. Im zweiten Teil dieser Arbeit wird mit optischen Anregungen untersucht, ob eine Kopplung zwischen dem Spinsystem und dem elektronischen System in dem magnetischen Halbleiter α-MnTe existiert. Dazu wird eine 200 nm dicke Schicht α-MnTe mit verschiedenen experimentellen Methoden vermessen. Die Bandlücke von α-MnTe ist um einen zusätzlichen Beitrag in der antiferromagnetischen Phase blauverschoben, welcher proportional mit der Untergittermagnetisierung skaliert. Diese statische Kopplung zwischen der Bandlücke und dem Spinsystem wird erfolgreich in unserer Probe reproduziert. Darauf aufbauend wird die Dynamik der Bandlücke unter Verwendung des Pump-Probe Verfahrens untersucht. Die transiente Reflektivität zeigt, dass die Bandlücke durch das optisch aktive α-Phonon kohärent moduliert wird. Im finalen Schritt wird die Bandlücke kohärent angeregt und die Antwort des Spinsystems, die Rotation der Polarisation, detektiert. Diese ist ebenfalls durch das α-Phonon kohärent moduliert und zeigt einen zusätzlichen inkohärenten Beitrag in der antiferromagnetischen Phase, welcher eindeutig auf die magnetische Ordnung zurückzuführen ist. Die Zerfallszeit dieses Beitrags entspricht der der Zeitskala der Untergitterdemagnetisierung. Somit konnte in dieser Arbeit eine phonongestützte Kopplung zwischen dem elektronischen System und dem Spinsystem in α-MnTe gezeigt werden.