ИСТИНА

MAX-phases are the relatively new class of compounds with the common Mn+1AXn chemistry, where M is an early transition metal, A is an A-group element and X is either C or N. Due to the natural nano-lamellar crystal structure MAX-phases combine metallic and ceramic properties such as high values of electronic and thermal conductivity, easy machinability, good tolerance to oxidation, mechanical damages and thermal shock. The major part of MAX-phases are paramagnets although some representatives such as (Cr1-xMnx)2AlC were anticipated to possess long-range magnetic ordering. Magnetism of MAX-phases is strongly correlated to the phase purity of the samples which is especially crucial for the bulk ones as the bulk synthesis techniques are frequently deficient to obtain the necessary quality. Besides, it’s problematic to successfully include dopant element, for example manganese, to the MAX-phase structure as the solubility limit is low for the major part of synthesis techniques. Herein we observe how the very initial method of the bulk MAX-phase synthesis, the arc melting technique, can be optimized for the sake of producing almost phase-pure samples of (Cr1-xMnx)2AlC MAX-phase. The optimization procedure was conducted in three steps. On the first step, Cr2AlC MAX-phase samples with different stoichiometry (2:x:1, x = 1 - 1.5) were produced in order to reveal the proper stoichiometry where the incorporation of the by-phases to the sample’s volume reaches its minimum. On the second step, other parameters of the synthesis process such as the pressure in the melting chamber and annealing time were taken into account and precisely investigated. Also samples melted from Cr3C2 and Al9Cr4 precursors and from the cold-pressed powder pellets were studied. On the third step manganese was added to the samples as the dopant element in order to explore its solubility limit and to prove the sufficiency of its incorporation to the MAX-phase structure. All the samples were investigated by means on the XRD and SEM-EDX analysis to both quantitatively and qualitatively observe their phase composition. The final series of (Cr1-xMnx)2AlC MAX-phase samples with x = 0, 0.025, 0.05 and 0.1 was produced by means of the fully optimized arc melting technique. Their structural properties and phase purity was also confirmed using XRD and SEM-EDX techniques. Their magnetism was explored by SQUID magnetometry. M vs H curves taken both at the room temperature and at 2 K both with the M vs T dependency in the range from 2 K to 350 K revealed the canted antiferromagnetic (AFM) state in the whole range of the studied temperatures. Manganese was successfully included to the MAX-phase structure and enhanced the net magnetic moment although not changing the resulting type of magnetic ordering. This result opens the way to further tune the magnetic properties of (Cr1-xMnx)2AlC MAX-phase and to possibly trigger the theoretically predicted AFM-FM transition which makes this compound promising for the variety of practical applications.