Correlations between stacked structures and weak itinerant magnetic properties of La2-xYxNi7compounds.

Hexagonal La2Ni7and rhombohedral Y2Ni7are weak itinerant antiferromagnet (wAFM) and ferromagnet (wFM), respectively. To follow the evolution between these two compounds, the crystal structure and magnetic properties ofA2B7intermetallic compounds (A= La, Y,B= Ni) have been investigated combining x-ray powder diffraction and magnetic measurements. The La2-xYxNi7intermetallic compounds with 0 ⩽x⩽ 1 crystallize in the hexagonal Ce2Ni7-type structure with Y preferentially located in the [A2B4] units. The compounds with larger Y content (1.2 ⩽x< 2) crystallize in both hexagonal and rhombohedral (Gd2Co7-type) structures with a substitution of Y for La in both [A2B4] and [AB5] units. Y2Ni7crystallizes in the rhombohedral structure only. The average cell volume decreases linearly versus Y content, whereas thec/aratio presents a minimum atx= 1 due to geometric constrains. The magnetic properties are strongly dependent on the structure type and the Y content. La2Ni7displays a complex metamagnetic behavior with split AFM peaks. Compounds withx= 0.25 and 0.5 display a wAFM ground state and two metamagnetic transitions, the first one toward an intermediate wAFM state and the second one toward a FM state.TNand the second critical fieldμ0Hc2increase with the Y content, indicating a stabilization of the AFM state. LaYNi7, which is as the boundary between the two structure types, presents a very wFM state at low field and an AFM state as the applied field increases. All the compounds withx> 1, and which contains a rhombohedral phase are wFM withTC= 53(2) K. In addition to the experimental studies, first principles calculations using spin polarization have been performed to interpret the evolution of structural phase stability for 0 ⩽x⩽ 2.