Public Thesis Defense of Alessandra CANETTA - IMCN
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Impact of magnetic order on the mechanical and thermoelectric properties of 2D magnets
Friday December 5, 2025 - 4:30pm - Auditorium CYCL01 - Marc de Hemptinne building - Chemin du Cyclotron 2, 1348 Louvain-la-Neuve
In two-dimensional (2D) materials, neighboring atoms are held together by strong in-plane covalent bonds and weak out-of-plane van der Waals (vdW) forces. Such particular structure confines the charge carriers along one direction, offering multiple advantages in terms of mechanical, electrical and thermal properties with respect to bulk systems. This thesis focuses on 2D magnets and how the magnetic ordering affects their thermoelectric and mechanical properties, in particular across magnetic phase transitions. A-type antiferromagnetic semiconductor Chromium Sulfide Bromide (CrSBr) and room temperature ferromagnetic metal Chromium Ditelluride(CrTe2) are investigated. First, the electrical and thermoelectric properties are recorded as a function of the temperature . CrSBr Seebeck coefficient α decreasing trend with temperature as well as its maximum at the phase transition temperature TN are associated with the spin-entropy contribution in the total thermopower. Applying an external magnetic field produces an increase in both α and the electrical conductance G, due to the reactivation of interlayer tunneling. G and α manifest similar dependences from temperature and magnetic field, leading to an enhancement of the power factor at TN. Temperature-dependent CrTe2 Seebeck coefficient shows instead a bow tie-like shape, attributed to different spin-entropy productions in the heating and cooling thermal processes. CrTe2 magnetic phase transition is also investigated by means of temperature-dependent Raman spectroscopy. Strong oscillations around the linear trend are reported in the case of the out-of-plane A1g mode. Ultrasonic Force Microscopy (UFM) is then introduced as an effective method to study the mechanical properties of 2D systems. A benchmark of the technique is done by measuring minimally twisted double bilayer graphene. Temperature-dependent UFM maps of CrTe2 are finally recorded, in order to identify changes in Young’s modulus across the magnetic phase transition. A discontinuity is indeed found around at the phase transition temperature, above which the amplitude of the signal tends to linearly increase.
Jury members :
Prof. Pascal Gehring (UCLouvain)(Supervisor)
Prof. Xavier Urbain (UCLouvain) (Chairperson)
Prof. Benoît Hackens (UCLouvain) (Secretary)
Prof. Jean-Christophe Charlier (UCLouvain)
Prof. Matthieu Verstraete (Université de Liège)
Prof. Martin Lee (Eindhoven University of Technology)