Magnetic Structure of CrAs and Mn-Substituted CrAs

Abstract

A neutron diffraction study has been made of powdered samples of CrAs and Mn‐substituted CrAs, namely, Cr_0.7Mn_0.3As, Cr_0.4Mn_0.6As, and Cr_0.3Mn_0.7As. Although CrAs shows a kink in susceptibility at 796°K, the anomaly was found to be due to a crystallographic transformation, from MnP‐type structure (low‐temperature side) to NiAs type. The liquid‐nitrogen temperature diffraction pattern contains a number of magnetic peaks. An analysis of the data gives a double‐layered helical structure, with the propagation vector along the c axis (the space group Pnma), like that found in MnP. The Néel temperature as determined from the temperature dependence of (101)⁻ intensity is about 280°K. The magnetic structure of Cr_0.7Mn_0.3As is much the same as that of CrAs, but with the Néel temperature at 263°K. Cr_0.4Mn_0.6As is ferromagnetic with a Curie temperature at 160°K, and has a magnetic transition in the paramagnetic range, which separates the low‐temperature low‐spin state from the high‐temperature intermediate‐spin state. Cr_0.3Mn_0.7As is metamagnetic at low temperatures.