Magnetostructural behavior in the non-centrosymmetric compound NdPd.

A systematic study of the physical properties and microscopic magnetism of NdPd compound, which in the paramagnetic state crystallizes in the non-centrosymmetric hexagonal ThFe-type structure (hP20-P6 mc; with a  =  10.1367(1) Å and c  =  6.3847(1) Å at 300 K), confirms multiple magnetic ordering transitions that occur upon cooling. Antiferromagnetic transition is observed at T   =  37 K, which is followed by ferromagnetic transformation at T   =  33 K. The first-order magnetic transition at T is magnetoelastic: it involves a change of crystal symmetry from P6 mc to Cmc2 and leads to anisotropic changes of the unit cell parameters. While the antiferromagnetic structure is symmetry allowed in P6 mc, the ferromagnetic structure with magnetic moments along the a-direction of the original hexagonal unit cell induces the first order transition to Cmc2. Density functional theory calculations confirm the experimentally observed ground state with the a-axis as the easy magnetization direction.