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arXiv · 1704.08100

Ordering tendencies and electronic properties in quaternary Heusler derivatives

Pascal Neibecker·Markus E. Gruner·Xiao Xu·Ryosuke Kainuma·Winfried Petry·Rossitza Pentcheva·Michael Leitner
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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 L2$_1$ 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 1160 K. In contrast, in NiCoMnAl slow cooling or low-temperature annealing treatments are required to induce incipient L2$_1$ ordering, otherwise the system displays only B2 order. Linked to this L2$_1$ 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 pseudo-gap emerges in the minority spin channel only for the completely ordered Y structure, which however is energetically unstable compared to the predicted ground state of a tetragonal structure with alternating layers of Ni and Co. The experimental inaccessibility of the totally ordered structures is explained by kinetic limitations due to the low ordering energies.

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Pascal Neibecker, Markus E. Gruner, Xiao Xu, Ryosuke Kainuma, Winfried Petry, Rossitza Pentcheva, Michael Leitner. 2017-04-26. Ordering tendencies and electronic properties in quaternary Heusler derivatives. https://doi.org/10.1103/physrevb.96.165131

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