Seminar DON, axes 1 and 4 presented Abdelghani Laraoui

Abdelghani Laraoui (Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln)

Abstract :
Magnetic microscopy based on nitrogen vacancy (NV) centers in diamond has become a versatile tool to detect magnetic fields with an unprecedented combination of spatial resolution and magnetic sensitivity, opening up new frontiers in biological [1] and condensed physics matter research [2]. In this seminar, I will present two examples of using NV magnetic microscopy in both scanning probe microscopy (SPM) and wide-field microscopy (WFM) geometries to study nanoscale magnetic phenomena in different materials. First, I will discuss NV-SPM measurements of antiferromagnetic (AFM) domains switching in Cr2O3 and B-Cr2O3 thin films and device structures [3, 4]. Cr2O3 is an archetypical AFM oxide that permits voltage-control of the Néel vector. In addition, boron doping increases Néel temperature from 307 K to 400 K and allows realizing voltage controlled Néel vector at zero applied magnetic field, a promising finding to AFM spintronics. Then, I will discuss NV-WFM measurements on individual Fe(Htrz)2(trz)](BF4)] (Fe triazole) spin-crossover (SCO) nano-rods of size varying from 20 to 1000 nm [5]. Fe triazole SCO complexes exhibit thermal switching between low spin (LS) and high spin (HS) states which are applicable in thermal sensors and molecular switches. While the bulk magnetic properties of these molecules are widely studied by bulk magnetometry techniques their properties at the individual level are missing. The stray magnetic fields produced by individual Fe-triazole nano-rods are imaged by NV magnetic microscopy as a function of temperature (up to 150 0C) and applied magnetic field (up to 3500 G). We found that in most of the nanorods the LS state is slightly paramagnetic, possibly originating from the surface oxidation and/or the greater Fe(III) presence along the nanorods’ edges [5].

References: [1] I. Fescenko, A. Laraoui, et al., Phys. Rev. App. 11, 034029 (2019). [2] A. Laraoui and K.
Ambal, Appl. Phys. Lett. 121, 060502 (2022). [3] A. Erickson, A. Laraoui, et al., RSC Adv. 13, 178-185 (2023).
[4] A. Erickson, A. Laraoui, et al., to be submitted to Nat. Mat. (2023). [5] S. Lamichhane, A. Laraoui, et al.,
ACS Nano 17, 9, 8694–8704 (2023).

Contact : Valérie Halté (

Seminar DMONS : Maximilien BARBIER

Speaker : Maximilien BARBIER / Lecturer in Theoretical Physics/Applied Mathematics University of the West of Scotland, United Kingdom

Abstract :

Thermodynamics in its standard form applies to systems that are at equilibrium. It hence says very little about the processes that may drive a system from one equilibrium state to another. Describing such processes is the goal of nonequilibrium thermodynamics.

The study of nonequilibrium systems has originally been restricted to phenomena that occur near equilibrium. This approach yielded important results such as the celebrated Onsager-Casimir reciprocity relations or the fluctuation-dissipation theorem. Close to equilibrium, the response of the system depends linearly on the constraints that drive it out of equilibrium. This linear behavior breaks down as the system is driven farther away from equilibrium. Alternative methods are thus required to treat such nonlinear regimes. To this regard, exact results have been obtained in the form of the so-called fluctuation relations (or fluctuation theorems) whose main strength is to remain valid arbitrarily far from equilibrium.
In this talk, I will introduce some of the main ideas that underly nonequilibrium thermodynamics and discuss how fluctuation relations can be used to access the nonequilibrium properties of general systems. In particular, I will quantify the impact of a fluctuation relation on the full statistics of the nonequilibrium currents that take place in the system.

Pour tout contact :

Rodolfo JALABERT :

Dietmar WEINMANN :