Ordering tendencies and electronic properties in quaternary Heusler derivatives

Pascal Neibecker, Markus E. Gruner, Xiao Xu, Ryosuke Kainuma, Winfried Petry, Rossitza Pentcheva, Michael Leitner

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

The phase stabilities and ordering tendencies in the quaternary full-Heusler alloys NiCoMnAl and NiCoMnGa have been investigated by in situ neutron diffraction, calorimetry, and magnetization measurements. NiCoMnGa was found to adopt the L21 structure, with distinct Mn and Ga sublattices but a common Ni-Co sublattice. A second-order phase transition to the B2 phase with disorder also between Mn and Ga was observed at 1160K. In contrast, in NiCoMnAl slow cooling or low-temperature annealing treatments are required to induce incipient L21 ordering, otherwise the system displays only B2 order. Linked to L21 ordering, a drastic increase in the magnetic transition temperature was observed in NiCoMnAl, while annealing affected the magnetic behavior of NiCoMnGa only weakly due to the low degree of quenched-in disorder. First principles calculations were employed to study the thermodynamics as well as order-dependent electronic properties of both compounds. It was found that a near half-metallic pseudogap emerges in the minority spin channel only for the completely ordered Y structure. However, this structure is energetically unstable compared to a tetragonal structure with alternating layers of Ni and Co, which is predicted to be the low-temperature ground state. The experimental inaccessibility of the totally ordered structures is explained by kinetic limitations due to the low ordering energies.

Original languageEnglish
Article number165131
JournalPhysical Review B
Volume96
Issue number16
DOIs
Publication statusPublished - 2017 Oct 16

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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