Papers by Author: K.R.A. Ziebeck

Abstract: X-ray powder diffraction, permeability, magnetization and differential scanning calorimetry measurements were carried out on the magnetic shape memory alloys Ni2MnGa1−xCux (0 ≤ x ≤ 0.25). On the basis of the experimental results, the phase diagram in the temperature– concentration plane was determined for this alloy system. The determined phase diagram is spanned by the paramagnetic austenite phase (Para-A), paramagnetic martensite phase (Para-M), ferromagnetic austenite phase (Ferro-A), ferromagnetic martensite phase (Ferro-M) and the premartensite phase. It was found that the magnetostructural transition between the phases Para-A and Ferro-M can occur in the concentration region 0.12 < x ≤ 0.14 and that Ni2MnGa1−xCux has the characteristics of the phase diagram similar to those of the phase diagrams of Ni2+xMn1−xGa and Ni2Mn1−xCuxGa. In order to understand the phase diagram, the phenomenological free energy as a function of the martensitic distortion and magnetization was constructed and analyzed.

Abstract: X-ray powder diffraction and magnetization measurements were done on the magnetic shape memory alloys Ni2Mn1+xSn1-x. The alloys with 0≤x≾0.4 crystallize in the cubic L21 structure and exhibit the ferromagnetic behavior. X-ray diffraction patterns indicate that the excess Mn atoms occupy the Sn sites. Furthermore, magnetization measurements make clear that the Mn atoms, which substitute for Sn sites, are coupled antiferromagnetically to the ferromagnetic manganese sublattices. The alloys with 0.4≾x≤0.6 undergo a martensitic transition from the high temperature L21 structure to the orthorhombic 4O one. These alloys show a variety of magnetic transitions. A magnetic phase diagram of Ni2Mn1+xSn1-x system is discussed qualitatively on the basis of the interatomic dependence of the exchange interactions.