Effects of Si substitution on phase transformation and exchange bias in Ni-Mn-In ribbons

The effects of partial Si substitution for In on phase transformation and exchange bias (EB) behaviour in as-spun and annealed Ni48Mn39In13-xSix (x 0-4) ribbons have been investigated. It was observed that an increase in Si concentration strongly affects the magnetic state of the martensitic phase and the EB properties of the ribbons. Both martensitic transition temperature (TM) and the Curie temperature (TC) of the austenitic phase decrease with increasing Si concentration for x 3, while the ribbon for x 4 possess the modulated martensitic monoclinic structure at room temperature, but its magnetization is unlike (considerably smaller than) those of other ribbons. Both the exchange bias field (HE) and the coercivity (HC) are strongly dependent on Si content. The values of HE and HC vary from 216 Oe and 314 Oe to 434 Oe and 1682 Oe, respectively, for the as-spun ribbons at 10 K after cooling in a field of 20 kOe, as x is increased from 0 to 4, while they change from 258 Oe and 192 Oe to 456 Oe and 1488 Oe for the annealed ones. The EB phenomena are attributed to the exchange interactions that occurred in AFM-FM interfaces in Si-substituted Ni-Mn-In ribbons.