arXiv subjects

T. Zalewski

Publications and source records attributed to T. Zalewski.

5 recordsLinked to original sources

arXiv2026

A crystal-field route to THz-driven magnetization

Light carries angular momentum, but the microscopic pathways that transform it into magnetization remain elusive. Here we establish that crystal-field excitations, historically viewed primarily as equilibrium spectroscopic fingerprints of localized 4$f$ electrons, constitute an active microscopic route through which circularly-polarized terahertz (THz) light creates magnetic polarization. Using wavelength-selective ultrafast Faraday spectroscopy on the paramagnetic insulator CeF$_3$, we show that resonant excitation of localized 4$f$ crystal-field transitions generates a helicity-dependent magnetization that survives for up to about 100 ps. Most strikingly, while the optical helicity is held fixed, the THz-driven response reverses sign as the excitation wavelength is tuned across the crystal-field resonance. The resulting dispersive spectral response follows the crystal-field excitation spectrum rather than that of optical phonons, and is captured by resonant electronic theory of the inverse Faraday effect. Our results identify crystal-field excitations as a previously unrecognized dynamical reservoir for optical angular momentum and broaden the microscopic pathways through which THz light can create and manipulate magnetic states.

cond-mat.mtrl-sci↗

arXiv2023

Coherent control of photomagnetic back-switching by double-pump laser pulses

The control of nonthermal, all-optical magnetization switching under the regime with an independent state of laser polarization opens up new opportunities for ultrafast magnetic recording. Here, we investigate the photo-magnetic back-switching capabilities of the write and erase magnetic domain pattern using double-pump pulse excitations in an iron garnet film with pure cubic magnetocrystalline symmetry. It is essential to note that forward and backward magnetization switching is achievable in two distinctive scenarios: using identical linearly polarized laser pulses and with pulses having orthogonal polarization planes. By observing the switch of magnetization at domains independent of the initial state, one can nonthermally toggle the magnetization, equivalent to XOR logical operation, at frequencies reaching up to 50 GHz.

cond-mat.mtrl-sci↗

arXiv2023

Ultrafast all-optical toggle writing of magnetic bits without relying on heat

While in accordance with Curie's principle, one would intuitively expect that symmetry of the cause has to be found in the symmetry of the effect, ultrafast excitation of matter is able to violate this principle. For instance, it is believed that heating alone, obviously not having the symmetry of a magnetic field, cannot result in a deterministic reversal of magnetization. However, if the heating is induced by a femtosecond laser pulse and thus ultrafast, it does facilitate toggle switching of magnetization between stable bit-states without any magnetic field at all. Here we show that the regime of ultrafast toggle switching can be also realized via a mechanism without relying on any heat. The obvious mismatch between symmetries of the cause and the response can thus be seen as a violation of Curie's principle. In particular, ultrafast laser excitation of iron-garnet with linearly polarized light modifies magnetic anisotropy and thus causes toggling magnetization between two stable bit states. In contrast to the laser-heat-induced magnetization reversal, this new regime of 'cold' toggle switching can be observed in ferrimagnets without the compensation point and in an exceptionally broad temperature range. The control of magnetic anisotropy required for the toggle switching is accompanied by lower dissipations, than in the mechanism of laser-induced-heating, but the dissipations and the switching-time are shown to be competing parameters.

cond-mat.mtrl-sci↗

arXiv2023

Non-reciprocal coherent all-optical switching between magnetic multi-states

We present experimental and computational findings of the laser-induced non-reciprocal motion of magnetization during ultrafast photo-magnetic switching in garnets. We found distinct coherent magnetization precession trajectories and switching times between four magnetization states, depending on both directions of the light linear polarization and initial magnetic state. As a fingerprint of the topological symmetry, the choice of the switching trajectory is governed by an interplay of the photo-magnetic torque and magnetic anisotropy. Our results open a plethora of possibilities for designing energy-efficient magnetization switching routes at arbitrary energy landscapes.

cond-mat.mtrl-sci↗

arXiv2021

Single-shot imaging of ultrafast all-optical magnetization dynamics with a spatio-temporal resolution

We present a laboratory system for single-shot magneto-optical (MO) imaging of ultrafast magnetization dynamics with high-sensitivity of MO rotation. We create a stack of MO images repeatedly employing a single pair of a pump and defocused probe pulses to induce and visualize MO changes in the sample. Both laser beams are independently wavelength-tunable allowing for a flexible, resonant adjustable two-color pump and probe scheme. To increase the MO contrast the probe beam is spatially filtered. We performed the all-optical switching experiment in Co-doped yttrium iron garnet films (YIG:Co) to demonstrate the capability of the presented method. We determine the spatial-temporal distribution of the effective field of photo-induced anisotropy driving the all-optical switching of the magnetization in YIG:Co film without an external magnetic field. Moreover, using this imaging method, we tracked the process of the laser-induced magnetization precession.

cond-mat.mtrl-sci↗