Temperature and coupling
Understanding the effects of temperature on the magnetic properties of magnetically coupled nanostructures reveals the fundamental mechanisms of these couplings. Also, this understanding makes it possible to examine and anticipate the stability of devices that are subjected to temperature variations. For these reasons, many research and development studies focus on temperature behaviour. Materials are generally subjected to temperature variations by passing below the magnetic ordering temperature (Curie, Neel and/or Blocking temperatures).
In addition, the understanding of magnetic effects on temperature within materials is given particular attention through magnetocaloric and hyperthermia effects. The former would allow refrigeration technologies to be modified while the latter is being explored for medical applications in the localized treatment of malignant cells. The use of magnetic nanostructures to achieve these effects is attracting increasing interest. Many questions remain open, in particular the interest of coupling in multilayers to obtain a high magneto-caloric effect, or of internal coupling to nanoparticles for hyperthermal effects.
All these studies are carried out in close collaboration with the Department of Physics at the University of Johannesburg.
In recent years, we have studied the temperature behaviour of exchange-coupled bilayers and have demonstrated the non-stability of magnetic energies below the scheduling, Curie, Neel and blocking temperatures. This type of study demonstrates, and allows the quantification of the temperature sensitivity of devices based on the magnetic properties of these nanostructures. [J. Richy Thèse Brest 2016, INTERMAG 2015]
1. we have undertaken to characterize the angular and temperature behaviour of multi-ferroic materials coupled by exchange. For this purpose, we have developed an immersion cryostat allowing measurements at 77K and integrating into our vector magnetometer with vibrating sample.
2. we have developed a theoretical model to determine the magnetic reversal of exchange-coupled nanoparticles. The originality of this work is that it includes the dispersion in sizes of an assembly of nanoparticles. This template is available in open source by following the following link: https://github.com/LabMagUBO/StoneX.
3. we are currently developing studies on nanoparticles in order to characterize their temperature properties with the objective of experimentally characterizing hyperthermal, and/or magnetocaloric properties.
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