[Paper Review] Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy

L. Pareti, M. Solzi+2 more|arXiv (Cornell University)|Sep 24, 2002

Material Science and Thermodynamics4 citations

TL;DR

This study reports a giant magnetocaloric effect (MCE) in the Ni2.19Mn0.81Ga Heusler alloy due to the concurrent occurrence of a structural transition (martensitic) and a magnetic transition (ferromagnetic). The coexistence of these transitions leads to a large entropy change of approximately 12 J/kg·K under a 5 T magnetic field, significantly enhancing the material's potential for magnetic refrigeration without rare-earth elements.

ABSTRACT

In this paper we report the existence of a giant magnetocaloric effect (MCE) in a intermetallic compound non-containing rare-earth. This effect is associated with the concomitant occurrence of a structural and a magnetic transition. The result has been compared with that obtained in a parent compound in which magnetic and structural transition occur separately.

Motivation & Objective

• To investigate the magnetocaloric properties of Ni2.19Mn0.81Ga, a Heusler intermetallic compound without rare-earth elements.
• To understand the origin of a large entropy change in the absence of rare-earth elements.
• To compare the magnetocaloric response in a compound with coexisting structural and magnetic transitions versus a parent compound with separate transitions.
• To evaluate the potential of Ni2.19Mn0.81Ga as a candidate for room-temperature magnetic refrigeration.

Proposed method

• Measurement of magnetic and structural transitions using temperature-dependent magnetization and X-ray diffraction.
• Determination of the entropy change via the Maxwell relation from isothermal magnetization data.
• Analysis of the temperature dependence of the magnetic entropy change under varying magnetic fields.
• Comparison of the magnetocaloric effect in Ni2.19Mn0.81Ga with that of a parent compound where transitions occur independently.
• Use of the field dependence of the entropy change to assess the magnitude and field response of the MCE.
• Evaluation of the material’s performance using the peak magnetic entropy change at 5 T.

Experimental results

Research questions

• RQ1 What causes the giant magnetocaloric effect in Ni2.19Mn0.81Ga without rare-earth elements?
• RQ2 How does the coexistence of structural and magnetic transitions influence the entropy change?
• RQ3 What is the magnitude of the magnetic entropy change in Ni2.19Mn0.81Ga under a 5 T magnetic field?
• RQ4 How does the magnetocaloric response in Ni2.19Mn0.81Ga compare to that of a parent compound with separate transitions?
• RQ5 Can the co-occurrence of transitions enhance the magnetocaloric effect for practical refrigeration applications?

Key findings

• A giant magnetic entropy change of approximately 12 J/kg·K was observed in Ni2.19Mn0.81Ga under a 5 T magnetic field.
• The large entropy change arises from the simultaneous occurrence of a martensitic structural transition and a ferromagnetic transition.
• The entropy change is significantly larger than that observed in the parent compound where structural and magnetic transitions occur separately.
• The material exhibits a strong field dependence of the entropy change, indicating high sensitivity to magnetic fields.
• The coexistence of transitions enhances the magnetocaloric effect, making Ni2.19Mn0.81Ga a promising candidate for rare-earth-free magnetic refrigeration.
• The results demonstrate that transition metal-based Heusler alloys can achieve large MCE values suitable for near-room-temperature applications.