Methods for the analysis of thermomagnetic phase transitions of magnetocaloric materials

This thesis focuses on the analysis of the relation between thermomagnetic phase transitions and magnetocaloric response of materials. First, various experimental factors that can a ect the measurements of the magnetocaloric e ect and can potentially cause misleading interpretation or artifacts are studied with the aid of experimental data and numerical calculations. These are sample geometry, compositional inhomogeneities, low temperature limitation in heat capacity measurements and measurement protocols in direct techniques. After that, it is shown that the analysis of the magnetic eld dependence of the magnetocaloric e ect is useful for obtaining information of thermomagnetic phase transitions, such as Curie temperature, critical exponents (even in biphasic systems), order of the phase transition and critical composition for which rst order phase transition becomes second order. These analyses were performed in well know materials such as Gd, Gd5Si2Ge2, La(Fe,Si)13, Ni-Mn-In Heusler alloys and Fe-, Co-, Ni-amorphous and nanocrystalline alloys. Next, various possible avenues to optimize the magnetocaloric behavior by tapping on the characteristics of rst and second order phase transition type systems were investigated. For second order phase transition type, the coe cient of refrigerant performance was optimized as a function of the amount of the various phase fractions in Gd-GdZn composite, while an enhanced magnetic eld responsiveness is achived in nanostructured Gd/Ti multilayers. For rst order phase transition type, reduction of hysteresis and enhancement of rst order character is achieved in Ni- and Cr-doped La(Fe,Si)13 compounds, respectively.

Author dc:creator

• Moreno Ramírez, Luis Miguel

Advisors dc:contributor.advisor

• Conde Amiano, Alejandro
• Franco García, Victorino

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 Internacional

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/11441/88165

OAI identifier oai:identifier

oai:idus.us.es:11441/88165