Speaker
Description
Magnetocaloric cooling is being widely studied for its multifaceted applications such as magnetic refrigeration, liquefaction of gases, hyperthermia, etc. Magnetocaloric effect (MCE) involves the cooling/heating of a magnetic material under adiabatic magnetic field change. Rare-earth-based materials exhibit large MCE due to their inherently large magnetic moment but are not sustainable. Transition metals-based MCE materials are therefore gaining momentum and are being engineered in multiple ways to maximize the MCE.
Our work is centered on producing textured polycrystalline samples of transition metals-based alloys with a pronounced magnetocrystalline anisotropy. This will enable us to tap into the rotational magnetocaloric effect (RMCE) which would generate a larger magnetic entropy change than the traditional MCE. In this pursuit, we are using ‘Magnetic Slip Casting’ to synthesize textured polycrystals. The target alloy is prepared by arc melting or solid-state synthesis, post which it is subjected to ball milling to reduce the particle size. Using a suitable solvent like absolute ethanol and a stabilizing agent such as polyethylenimine, a stable slurry is prepared and casted into a silica tube mounted on an alumina support with a membrane filter. Over a few hours, the solvent dries up leaving behind a pellet. If this process is done in the presence of a small magnetic field, the crystals can be aligned along the magnetic easy axis, resulting in a crystallographically textured green body. This method requires tremendous optimization of several parameters like particle size, solvent-to-powder ratio, pH of the slurry, etc. However, this technique will be an effective process and has, so far, not been used to produce magnetocaloric materials.
We are focusing on Mn$_{x}$Fe$_{5-x}$Si$_{3}$ and (Mn,Fe)$_{2}$(P,Si) materials as they have strong magnetocrystalline anisotropy with an easy ab plane and an easy c-axis, respectively [1,2]. The textured sample when rotated in a constant magnetic field from its easy to hard direction, exhibits a sizeable magnetic entropy change. RMCE is generally observed in single crystals, which are tedious to grow, and mimicking the same effect by the proposed method will prove to be competent.
Acknowledgements
The project MagRota is funding by Normandy Region under the program « Normandie Recherche - Labels d'excellence» (n°23E06217)
References
[1] L. Caron et al., “Magnetocrystalline Anisotropy and the Magnetocaloric Effect in Fe$_2$P”, Physical Review B, vol. 88, no. 9. American Physical Society (APS), Sep. 30, 2013. https://doi.org/10.1103/physrevb.88.094440
[2] H. Yibole et al., “Magnetic properties, anisotropy parameters and magnetocaloric effect of flux grown MnFe4Si3 single crystal,” Journal of Magnetism and Magnetic Materials, vol. 504. Elsevier BV, p. 166597, Jun. 2020. https://doi.org/10.1016/j.jmmm.2020.166597
