Magnetic structure and transitions ofDy2Ni2Pb

Abstract

We have studied the magnetic structure and magnetic properties of the orthorhombic compound ${\mathrm{Dy}}_{2}{\mathrm{Ni}}_{2}\mathrm{Pb}$ by means of neutron-diffraction and bulk measurements. The bulk measurements (susceptibility, resistivity, and specific heat) suggest two distinct magnetic phase transitions: one antiferromagnetic at ${T}_{N}=14.5\mathrm{K}$ and the other at ${T}_{m}=3.5\mathrm{K},$ below which a ferrimagnetic or canted ferromagnetic structure is anticipated. On the contrary, neutron-diffraction measurements, which were made in the range 1.5--20 K, showed that ${\mathrm{Dy}}_{2}{\mathrm{Ni}}_{2}\mathrm{Pb}$ has a complicated noncollinear antiferromagnetic spin structure in the whole temperature range studied. The magnetic structure is described by two commensurate propagation vectors ${\mathbf{q}}_{1}=(0,0,0)$ and ${\mathbf{q}}_{2}=(1/3,0,0)$ with Dy moments confined to the $a\ensuremath{-}c$ plane. A smooth development of ${\mathbf{q}}_{1}$ and ${\mathbf{q}}_{2}$ magnetic-moment components at low temperatures indicates that the magnetic structure remains antiferromagnetic. We attempt to reconcile both bulk and neutron results. The possibility of another order-order magnetic phase transition at lower temperature is suggested.