Neutron diffraction investigation of the magnetic structure and magnetoelastic effects inNdMnO3

Abstract

We investigated the evolution of the magnetic structure and magnetoelastic effects ofNdMnO3 by neutron powder diffraction. We confirmed the A-type antiferromagnetic (AF) structure ofNdMnO3 belowTN≈82 K with magneticmoments parallel to the b axis of the orthorhombic crystal structure (space groupPbnm). We found that the magnetic moments of Nd order below aboutTN(Nd)≈20 K in a ferromagnetic structure with moments parallel to thec axis.At the same temperature the magnetic moments of Mn develop a ferromagnetic component parallel tothe c axis. We found strong magnetoelastic effects associated with the AF transition atTN≈82 K. The effect is veryprominent for the b lattice parameter. All three lattice parameters and therefore the unit cell volume contracts atTN≈82 K. We treated quantitatively the magnetoelastic effect of theb lattice parameter and found that the extra change in the lattice parameterΔb due to the magnetoelastic effect is proportional to the magnetic moment of the Mnion. We also determined the critical exponent of the AF phase transition to beβ = 0.296 ± 0.008.