Magnetic and transport properties in the Heusler series Ni2−xMn1+xSn affected by chemical disorder

• Crystal structure, magnetic and transport properties of Ni2−xMn1+x Sn have been studied.
• Development of a nomenclature, describing the transition metal type of disorder in Heusler alloys.
• First-principle calculations are in reasonable agreement with the experiments.
• Discussion of simple rules, predicting the ordering of the transition metals at high temperature.

Crystal structure, magnetic and transport characteristics of Ni2−x Mn1+x Sn Heusler series have been studied with the emphasis on chemical disorder effects. It is shown that the structure and the disorder character in these series can be predicted by using simple rules. Ni2 MnSn is a ferromagnetic, congruent melting phase, which crystallizes cubic in the L21 structure type. By increasing x, Ni and Mn atoms randomly mix and occupy the heterocubic sites of the regular Heusler structure, and the magnetic structure becomes ferrimagnetic. The total magnetic moment msat decreases linearly in the range 0.2 ≤ x ≤ 1, while the Curie temperature TC increases. At low Mn content (x < 0.2), the unit cell volume shows anomalous behavior, characterized by constant msat and TC. Electrical resistivity, Seebeck coefficient, and thermal conductivity strongly depend on the amount of disorder, which increases with the Mn content. Results of first-principle calculations based on the coherent potential approximation (CPA) alloy theory for the magnetic and electrical properties are in reasonable agreement with the simple rules and all experimental data.

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