Relation between the weak itinerant magnetism in A2Ni7 compounds ( A = Y, La) and their stacked crystal structures - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Physics: Condensed Matter Année : 2020

Relation between the weak itinerant magnetism in A2Ni7 compounds ( A = Y, La) and their stacked crystal structures

Résumé

The weak itinerant magnetic properties of A2Ni7 compounds with A  =  {Y, La} have been investigated using electronic band structure calculations in the relation with their polymorphic crystal structures. These compounds crystallizes in two structures resulting from the stacking of two and three blocks of [A2Ni4  +  2 ANi5] units for hexagonal 2H-La2Ni7 (Ce2Ni7 type) and rhombohedral 3R-Y2Ni7 (Gd2Co7 type) respectively. Experimentally, 2H-La2Ni7 is a weak itinerant antiferromagnet whereas 3R-Y2Ni7 is a weak itinerant ferromagnet. From the present first principles calculation within non-spin polarized state, both compounds present an electronic density of state with a sharp and narrow peak centered at the Fermi level corresponding to flat bands from 3d-Ni. This induces a magnetic instability and both compounds are more stable in a ferromagnetic (FM) order compared to a paramagnetic state (ΔE  ≈  −35 meV/f.u.). The magnetic moment of each of the five Ni sites varies with their positions relative to the [A2Ni4] and [ANi5] units: they are minimum in the [A2Ni4] unit and maximum at the interface between two [ANi5] units. For 2H-La2Ni7, an antiferromagnetic (AFM) structure has been proposed and found with an energy comparable to that of the FM state. This AFM structure is described by two FM unit blocks of opposite Ni spin sign separated by a non-magnetic layer at z  =  0 and ½. The Ni (2a) atoms belonging to this intermediate layer are located in the [La2Ni4] unit and are at a center of symmetry of the hexagonal cell (P63/mmc) where the resultant molecular field is cancelled. Further non-collinear spin calculations have been performed to determine the Ni moment orientations which are found preferentially parallel to the c axis for both FM and AFM structures
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Dates et versions

hal-02436487 , version 1 (01-10-2020)

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J-C Crivello, V. Paul-Boncour. Relation between the weak itinerant magnetism in A2Ni7 compounds ( A = Y, La) and their stacked crystal structures. Journal of Physics: Condensed Matter, 2020, 32 (14), pp.145802. ⟨10.1088/1361-648x/ab6045⟩. ⟨hal-02436487⟩
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