Properties Of Ni2MnGa Research Articles

Phase Constitution and Transformation Behavior of Ni<sub>2</sub>MnGa-Cu<sub>2</sub>MnAl Pseudobinary Intermetallic Compounds

The phase constitution, lattice parameter, martensitic and magnetic transformation behavior and hardness of the Ni2MnGa-Cu2MnAl pseudobinary alloys designed as (Ni2MnGa)x(Cu2MnAl)1-x were investigated in order to improve magnetic properties of Ni2MnGa. It was revealed that L21 Ni2MnGa and Cu2MnAl make a continuous solid solution of (Ni,Cu)2Mn(Ga,Al) when heat treated at 1073K, and that the lattice parameter of the L21 phase increases monotonously with increasing the compositional ratio x, that is, the amount of Cu2MnAl. Curie temperature TC also increases with increasing x. On the other hand, the martensitic transformation temperature of Ni2MnGa seems to decrease rapidly by adding Cu2MnAl. Hardness of the alloys heat-treated at 1073K ranges from HV200 to HV370, and solution hardening was recognized by mixing. When heat treated at 773K, a phase decomposition from L21 phase to Cu9Al4 and b-Mn was confirmed in the Cu2MnAl-rich alloys. The phase decomposition causes a decrease in the lattice parameter of L21 phase and TC and a significant increase in hardness.

The influence of atomic order and residual strain on the magnetic and structural properties of Ni2MnGa

Abstract The effect of atomic order and residual strain on the magnetic and structural properties of the ferromagnetic shape memory compound Ni2MnGa has been investigated using magnetisation and neutron diffraction measurements.

Dynamical properties of Ni2MnGa determined from density functional calculations

The phonon spectrum for Ni2MnGa in the cubic L21 structure has been calculated by using density functional theory. Several vibrational anomalies have been found at particular wave vectors, which are related to experimentally observed phase transformations leading to different modulated structures. The cubic L21 structure has been found to be unstable at zero temperature with respect to a particular rearrangement of the atoms which can be related to the TA2 phonon mode. The dispersion of optical phonons of the Ni atoms lies in a relatively low energy window, which leads to a hybridization with acoustic phonons emphasizing the role of a strong electron–phonon coupling in Ni2MnGa.

Lattice instability of Ni2MnGa

Anomalies have been detected in the temperature behavior of the physical properties of Ni2MnGa in the temperature interval preceding the martensitic transformation, which is attributed to TA2 phonon mode condensation at T=TI>Tm (Tm is the martensitic transition temperature).