Magnetization and exchange-bias effect in powders of the Heusler Ni2MnSn-based alloys

Experimental investigation of properties of powders of the Heusler Ni ₂ MnSn-based alloys revealed the extreme suppression of both, the magnetization and the exchange-bias and exchange spring effects in powders of the alloys. Furthermore, the structural transformation between austenite and martensite phases of the alloys is hindered in the powders, hysteresis curves do not exhibit saturation and observed cluster-glass behavior of the powders at low temperature is almost independent on magnetic field and on composition of the alloys. A complex conjunction of exchange-bias effect and frozen magnetization contribution has been revealed in the case of the powders. All the mentioned phenomena are strongly dependent on the size and the shape of particles of the powders prepared either in an agate mortar or in a ball mill. Temperature treatment of the powders and the compressed pellets at temperature 1173 K under argon led to a recovery of the applicable properties that are characteristic for the bulk alloys. Results of the earlier quantum mechanical calculations of effects of different arrangement of Mn and Sn atoms in crystal structure of the alloys have been used to discuss the observed properties of the powders and to assess a formation of clusters in magneto-crystalline structure of the alloys.