Origin of magnetocrystalline anisotropy in Ni-Mn-Ga-Co-Cu tetragonal martensite

•Magnetocrystalline anisotropy of Ni-Mn-Ga decreases with increasing Co and Cu concentration.•A deviation from stoichiometry results in decrease of the anisotropy.•The anisotropy decrease is larger for Cu in Ga sublattice compared to Mn sublattice.•The effect of Co on the anisotropy is only indirect...

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Bibliographic Details
Published inJournal of magnetism and magnetic materials Vol. 503; p. 166522
Main Authors Zelený, M., Straka, L., Rameš, M., Sozinov, A., Heczko, O.
Format Journal Article
LanguageEnglish
Published Amsterdam Elsevier B.V 01.06.2020
Elsevier BV
Subjects
Ab initio calculations
Anisotropy
Copper
Density functional theory
Magnetic moments
Magnetic shape memory
Magnetocrystalline anisotropy
Manganese
Martensite
Mathematical analysis
Maxima
Ni-Mn-Ga
Ni-Mn-Ga-Co-Cu
Nickel
Stoichiometry
Magnetocrystalline anisotropy
Magnetic shape memory
Ni-Mn-Ga-Co-Cu
Ab initio calculations
Ni-Mn-Ga
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Summary:•Magnetocrystalline anisotropy of Ni-Mn-Ga decreases with increasing Co and Cu concentration.•A deviation from stoichiometry results in decrease of the anisotropy.•The anisotropy decrease is larger for Cu in Ga sublattice compared to Mn sublattice.•The effect of Co on the anisotropy is only indirect caused by deficiency in Ni. We investigate the origin of magnetocrystalline anisotropy (MCA) in non-modulated martensite of Ni-Mn-Ga-Co-Cu exhibiting magnetic-field-induced strain up to 12%. Experiments as well as theoretical calculations using density functional theory show that Co and Cu doping or deviation from Ni2MnGa stoichiometry decreases the MCA. As follows from the calculations, the decrease of MCA is much stronger for Cu in Ga sublattice in comparison to Cu in Mn sublattice. The decreasing effect of Co on the MCA is only indirect caused by deficiency in Ni, which is the main element governing the MCA. For further insight, we calculated MCA and magnetic moment as a function of lattice tetragonality c/a. The MCA reaches a maximum at the same c/a where Ni magnetic moment is maximum. However, the tetragonality of equilibrium does not coincide with these maxima. Consequently, in contrast to common expectation, decreasing tetragonality from equilibrium can increase the MCA.
ISSN:0304-8853
1873-4766
DOI:10.1016/j.jmmm.2020.166522