arXiv subjects

Sebastien E. Hadjadj

Publications and source records attributed to Sebastien E. Hadjadj.

2 recordsLinked to original sources

arXiv2026

Atomic scale demonstration of ferromagnetism in a single layer FeCl2 on Au(111)

FeCl2 is a promising single-layer material with sizeable magnetic susceptibility and insulating character that can be easily grown by molecular beam epitaxy on various surfaces. In order to include it into the select palette of van der Waals materials used to engineer functional heterostructures, it is necessary to confirm its magnetic and electronic ground states, and understand the influence of the supporting substrate. In this work, we unambiguously demonstrate ferromagnetic ordering in a single-layer FeCl2 on Au(111) by means of spin-polarized scanning tunnelling microscopy. The material features a relatively wide insulating gap of 3.3 eV and a strongly spin-polarized conduction band that emerges at 1.5 eV above the Fermi level. Atomic scale defects with triangular shape play a primary role in the electronic gap and spin density distribution. Specifically, in a region of 1.6 nm around each defect, the conduction band is locally suppressed and the tunnelling magneto-conductance is reduced a factor of four. By tracking the spin-dependent tunnelling conductance as a function of the applied magnetic field, we record atomically resolved hysteresis loops, revealing a soft ferromagnetic ground state with pronounced out-of-plane anisotropy and coercive fields in the range of 15-50 mT.

cond-mat.mtrl-sci↗

arXiv2025

Studying all-optical magnetization switching of GdFe by double-pulse laser excitation

The tremendous interest in the technology and underlying physics of all-optical switching of magnetization brings up the question of how fast the switching can occur and how high the frequency of writing the data with ultrafast laser pulses can be. To answer this question, we excited a GdFe ferrimagnetic alloy, the magnetization of which can be reversed by single laser pulses, a phenomenon known as toggle switching, by two pulses with a certain time delay in between. Using photoemission electron microscopy and Kerr microscopy for magnetic domain imaging, we explore the effects of varying fluences of the first and second pulse as well as the time delay between the two pulses. Our results show that when the fluence of the first pulse is adjusted just above the threshold of single-pulse switching, a second pulse with about 60% of the fluence of the first pulse, arriving only 3 ps later, switches the magnetization back. This reswitching persists up to about 40 ps pulse separation. We interpret the latter as the time required for the sample to cool down and remagnetize after the first pulse. For shorter time delays below about 2 ps, no re-switching occurs. However, the effect of the two pulses adds up, enabling switching for fluences of both pulses below the threshold for single-pulse switching. Atomistic spin dynamics simulations are used to model the experimental data, successfully confirming our results.

cond-mat.mtrl-sci↗