Crystal and magnetic structure of antiferromagnetic Mn${}_2$PtPd

Abstract

We have investigated the crystal and magnetic structure of Mn${}_2$PtPd alloy using powder x-ray and neutron diffraction experiments. This compound is believed to belong to the Heusler family having crystal symmetry $I$4/$mmm$ (TiAl${}_3$-type). However, in this work we found that the Pd and Pt atoms are disordered and thus Mn${}_2$PtPd crystallizes in the $L$1${}_0$ structure having $P$4/$mmm$ symmetry (CuAu-I type) like MnPt and MnPd binary alloys. The lattice constants are $a$ = 2.86 à and $c$ = 3.62 à at room temperature. Mn${}_2$PtPd has a collinear antiferromagnetic spin structure below the Néel temperature $T$${}_N$ = 866 K, where Mn moments of $\sim$4 $\hat{I}¼$${}_B$ lie in the $ab$-plane. We observed a strong change in the lattice parameters near $T$${}_N$. The sample exhibits metallic behaviour, where electrical resistivity and carrier concentration are of the order of 10${}^{-5}$ $\hat{I}\text{c◯}$ cm and 10${}^{21}$ cm${}^{-3}$, respectively.