Magnetocaloric Effect, Structure, Spinodal Decomposition and Phase Transformations Heusler Alloy Ni-Mn-In.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Magnetism

Background:

• Heusler alloys, particularly Ni-Mn-In systems, are known for their magnetocaloric properties and phase transitions.
• Understanding the interplay between magnetic properties, temperature, and microstructure is crucial for optimizing their performance in magnetic refrigeration.

Purpose of the Study:

• To investigate the magnetocaloric effect of Ni46Mn41In13 Heusler alloy.
• To analyze the structural transformations and phase behavior as a function of temperature and sample thickness.
• To explore the relationship between concentration stratification and magnetic properties.

Main Methods:

• Magnetization measurements were performed as a function of temperature in magnetic fields up to 13.5 T.
• The magnetocaloric effect was measured directly under quasi-adiabatic conditions.
• Transmission electron microscopy (TEM) was used to study the alloy's structure at varying temperatures and foil thicknesses.

Main Results:

• A maximum magnetocaloric effect of ΔT_ad = -4.2 K was observed at 212 K under a 10 T magnetic field, coinciding with the martensitic transformation.
• Concentration stratification, potentially via spinodal decomposition, into nanoscale regions was identified in the temperature range of 353 K to 215 K.
• Martensitic phase with 14 M modulation was observed below 215 K for sample thicknesses > 50 nm, while thinner foils (< 50 nm) retained austenite from 353 K to 100 K.

Conclusions:

• The Ni46Mn41In13 alloy exhibits significant magnetocaloric properties linked to its martensitic transformation.
• Spinodal decomposition plays a role in the alloy's structural evolution.
• Sample thickness critically influences the observed phase behavior, particularly the retention of austenite at lower temperatures.