The Mg-Rich Phase NdNiMg₁₅: Structural and Magnetic Properties

Abstract

The intermetallic NdNiMg15 is the Mg-richest phase (more than 88 at% of Mg) discovered in the Mg-Nd-Ni system. Its structure was determined by X-ray diffraction on single-crystal with the following crystal data: tetragonal system, P4/nmm, Z = 2, a = 10.0602(1) Å, c = 7.7612(2) Å, dcalc = 2.40 g.cm -3 . Its structure is made of a 3-Dimensional framework of magnesium atoms showing channels filled by 1D chain consisting of alternating Nd and Ni atoms along the c-axis. Antiferromagnetic ordering was observed with TN = 9K, which is remarkably high considering the long distances between magnetic atoms, i.e Nd atoms. The effective magnetic moment eff is equal to 3.58 µB which is consistent with magnetic Nd 3+ ions and weakly or non-magnetic Ni-atoms. Below TN, the M(H) curves show field induced metamagnetic transitions at critical fields increasing with decreasing temperatures. The magnetic structure of NdNiMg15 was determined from neutron powder diffraction data by considering the propagation vector k = (½ ½ 0). This magnetic structure consists in ferromagnetic chains along the c-axis of Nd atoms carrying moments, only separated by Ni atoms. The chains are ferromagnetically coupled within planes perpendicular to the [110] direction and these planes are antiferromagnetically coupled to neighboring planes forming a checkerboard-like magnetic structure.