Luc Martin

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The chemical ordering in samples of Heusler alloys of the series Ni₂MnxV₁-xSn, where x stands for 1.0, 0.8, and 0.6, has been measured by neutron diffraction. Measurements were performed at room temperature. The samples were long thing single crystals with cross-section less than 1 mm. The samples had been cut by spark erosion from large single crystal boules. Extinction was still present. The data were fitted with a nuclear structure factor, allowing for chemical disorder, based on a model of the crystal structure. They highly order in the L2₁ type crystal structure. Slight Mn, V←→Ni disorder was sufficient to explain the data. For x=1.0, (3.5 ± 1.2) at % disorder between Mn-V and Ni atoms was necessary to obtain the best fit. For x=0.8 the best fit was obtained with no disorder. Disorder was (2.8 ± 0.9) at % between Mn-V and Ni atoms for the x=0.6 sample. No evidence of any other type of disorder was found.