Microstructural and magnetic characterization of materials

To understand properly the magnetic behavior of any material, an in-depth correlation with the microstructure is required since the different microstructural parameters (atomic order, internal strains, grain size, precipitates, dislocations, cracks, etc.) modify and control their physical and magnetic properties. So, our group has been working on the comparative microstructural and macroscopic magnetic characterization of different materials, such as ferrites and Fe oxide magnetic nanoparticles, Co-Fe based soft magnetic alloys, or magnetic shape memory alloys, especially Ni-Mn-Sn-Co and Ni-Mn-In-Co. This analysis is mainly performed through X-ray diffraction technique and magnetometry based on a SQUID magnetometer. Other techniques such as TEM or neutron diffractometry, are also used for this purpose employing external facilities. 

Particularly, our group is focussed on the study of the effect of defects in the magnetostructural properties of metamagnetic shape memory alloys. For example, one of the most interesting results obtained recently shows that in Ni-Mn-Sn-Co alloy, the sample subjected to soft-milling presents a higher magnetocaloric effect than in the sample where a thermal treatment to remove the induced defects was done. Another result shows how the increase of defects (internal strains) reduces the saturation magnetization of Ni-Mn-Sn alloy subjected to different thermal treatments.

• (1) Comparison of magnetocaloric effect analysis between a soft-milled sample (as-milled) and a sample with thermal treatment (annealed)
• (2) Saturation magnetization evolution with the induced defects (internal strains).

(1) Magnetocaloric effect experimented by a Ni-Mn-Sn alloy before and after thermal treatment.

(2) Evolution of its saturation magnetization with the induced crystallographic defects.

Contact: José Ignacio Pérez de Landazábal Berganzo