Compositional Dependence of Magnetocrystalline Anisotropy in Fe-, Co-, and Cu-Alloyed Ni-Mn-Ga

Michal Rameš,Vít Kopecký,Oleg Heczko

doi:10.3390/met12010133

Abstract

The key for the existence of magnetic induced reorientation is strong magnetocrystalline anisotropy, i.e., the coupling between ferroelastic and ferromagnetic ordering. To increase the transformation temperatures and thus functionality, various elemental alloying in Ni-Mn-Ga is tried. We analyzed more than twenty polycrystalline alloys alloyed by small amount (up to 5atom%) of transitional metals Co, Fe, Ni, and Cu for the value of magnetic anisotropy in search of general trends with alloying. In agreement with previous reports, we found that maximum anisotropy occurs at stoichiometric Ni2MnGa and any alloying decreases its value. The strongest decrease of the anisotropy is observed in the case where the alloyed elements substitute Ga.

Highlights

Magnetocrystalline anisotropy is a key parameter for existence of magnetically induced reorientation (MIR) [1], i.e., giant magnetic field induced strain enabled by twin boundary motion and consequent lattice reorientation [2]
A new impetus was provided by discovery of giant magnetic field induced strain (MFIS) in Ni-MSM effect: keeping Ni (Mn)-Ga in relatively modest field below 1 T close to room temperature [4]
The method does not provide precise values of the anisotropy, it supplies the useful comparative values and helps to evaluate anisotropy trend with elemental alloying. Such knowledge has a practical impact for the MIR effect, in particular alloys and for theoretical investigation, to guide their calculation being able to predict new magnetic shape memory (MSM) materials

Summary

Introduction

Magnetocrystalline anisotropy is a key parameter for existence of magnetically induced reorientation (MIR) [1], i.e., giant magnetic field induced strain enabled by twin boundary motion and consequent lattice reorientation [2]. The anisotropy was investigated by ferromagnetic resonance (FMR) method [22,23], but again, the polycrystalline and polytwinned martensite can result in a much lower anisotropy value [24] compared to single crystal due to averaging Another method is to use magnetization approach to saturation [3]. The method does not provide precise values of the anisotropy, it supplies the useful comparative values and helps to evaluate anisotropy trend with elemental alloying Such knowledge has a practical impact for the MIR effect, in particular alloys and for theoretical investigation, to guide their calculation being able to predict new magnetic shape memory (MSM) materials

Materials and Methods

Results and Discussion

Ni2MnGa substitution for element X