Mechanical hysteresis (MEH):  The magnetically induced reorientation (MIR) and MIR-related functionality is mediated by the motion of martensite twin boundaries, which is inevitably accompanied by mechanical hysteresis. A so-called twinning stress is a direct quantitative measure of MEH. The functionality can occur only when mechanical hysteresis (twinning stress) is very small. The fellow and his collaborators were the first to show that so-called Type 2 twin boundaries in Ni-Mn-Ga MSMAs can exhibit extremely low MEH (twinning stress of ~0.1 MPa) [1], about one order smaller than was previously reported. Moreover, they showed as first that such low MEH can be almost temperature independent for specially designed alloy compositions [2], while previously reported alloys typically showed strong temperature dependence. These scientific findings have strongly expanded the potential practical applicability of MSMAs.


Fig. 1. Extremely low mechanical hysteresis (~0.1 MPa) observed in Ni-Mn-Ga single crystals [3].

[1] A. Sozinov, N. Lanska, A. Soroka, L. Straka, App. Phys. Lett. 99 (2011) 124103-1.
[2] L. Straka, A. Sozinov, J. Drahokoupil, et al., J. App. Phys. 114 (2013) 063504-1.
[3] L. Straka,N. Lanska, K. Ullakko, A. Sozinov, Appl. Phys. Lett. 96, 131903 (2010); doi: