Magnetic Properties of Quaternary Selenides

We will investigate magnetic ordering in Cu2MGeSe4 (M = Mn, Fe, Co), for which magnetic susceptibility data indicate a transition to antiferromagnetic order at temperatures in the range 10–20 K. The Mn- and Co-containing phases exhibit Curie-Weiss behaviour at high temperatures with effective magnetic moments in good agreement with spin-only values. The Fe analogue exhibits more complex behaviour with a second feature observed in the susceptibility below TN and a broad maximum in the high-temperature susceptibility, leading to non-Curie-Weiss behaviour. We seek to determine the magnetic structure for each phase, and its evolution with temperature, by collection of data at base temperature and on warming through TN. We will extend the collections to higher temperature for the Fe analogue to understand the origin of the different behaviour exhibited by this phase.