Effects of the interplay between atomic and magnetic order on the properties of metamagnetic Ni-Co-Mn-Ga shape memory alloys

Journal Article · Fri Mar 21 04:00:00 EDT 2014 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4868055· OSTI ID:22271318

Ni-Co-Mn-Ga ferromagnetic shape memory alloys show metamagnetic behavior for a range of Co contents. The temperatures of the structural and magnetic transitions depend strongly on composition and atomic order degree, in such a way that combined composition and thermal treatment allows obtaining martensitic transformation between any magnetic state of austenite and martensite. This work presents a detailed analysis of the effect of atomic order on Ni-Co-Mn-Ga alloys through the evolution of structural and magnetic transitions after quench from high temperatures and during post-quest ageing. It is found that the way in which the atomic order affects the martensitic transformation temperatures and entropy depends on the magnetic order of austenite and martensite. The results can be explained assuming that improvement of atomic order decreases the free energy of the structural phases according to their magnetic order. However, it is assumed in this work that changes in the slope—that is, the entropy—of the Gibbs free energy curves are also decisive to the stability of the two-phase system. The experimental transformation entropy values have been compared with a phenomenological model, based on a Bragg–Williams approximation, accounting for the magnetic contribution. The excellent agreement obtained corroborates the magnetic origin of changes in transformation entropy brought about by atomic ordering.

• OSTI ID: 22271318
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 11 Vol. 115; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
APPROXIMATIONS
AUSTENITE
COBALT
COMPARATIVE EVALUATIONS
ENTROPY
FREE ENERGY
FREE ENTHALPY
GALLIUM
HEAT TREATMENTS
INTERMETALLIC COMPOUNDS
MANGANESE
MARTENSITE
NICKEL
PHASE DIAGRAMS
PHASE STABILITY
PHASE TRANSFORMATIONS
SHAPE MEMORY EFFECT
TEMPERATURE DEPENDENCE