Structure determination and magnetic properties of the Mn-doped MAX phase Cr2GaC

Abstract

Introducing magnetic elements into the structure of layered ternary transition metal-based carbides that belong to the family of MAX phases has led to various intriguing phenomena, such as magnetic ordering close to or even above room temperature and structural changes accompanying magnetic transitions. However, synthesizing manganese – or even iron-containing – MAX phases has proven to be extremely challenging as a result of the intrinsic structural instability at higher electron counts of the later transition metals as well as the favored formation of thermodynamically stable competing phases. Owing to the available kinetic control over the reaction product coupled with (atomically) precise growth techniques, the thin film community has taken the lead in the synthesis of MAX phases that exhibit magnetic ordering. Producing bulk samples of sufficient quality to study the complex magnetic properties of Mn-containing MAX phase compounds poses a major obstacle, particularly if conventional high-temperature methods are used that promote the formation of stable side phases. Using a milder wet chemical-based approach, we have synthesized Mn-containing solid solutions of MAX phase Cr₂GaC with Mn amounts ranging from 2 to 20 at% in the M-layers. The resulting (Cr_1−xMn_x)₂GaC (x = 0.02–0.2) particles are structurally characterized using X-ray and neutron powder diffractometry, as well as scanning transmission electron microscopy to enable detailed magnetometry studies. We demonstrate that low amounts of Mn on the Cr site do not induce magnetic ordering, and a sample with a Mn content of x = 0.20 is also predominantly paramagnetic. Taking all side phases into account, locally ordered parts of the MAX phase could explain the magnetic order we observe at elevated temperatures.