We report on vibrating reed measurements combined with density functional theory-based calculations to assess the elastic and damping properties of Fe-Pd ferromagnetic shape memory alloy splats. While the austenite-martensite phase transformation is generally accompanied by lattice softening, a severe modulus defect and elevated damping behavior are characteristic of the martensitic state. We interpret the latter in terms of twin boundary motion between pinning defects via partial 'twinning' dislocations. Energy dissipation is governed by twin boundary drag, primarily due to lattice imperfections, as concluded from the temperature dependence of damping and related activation enthalpies. Gesellschaft where the MSM effect was initially discovered [1-3] and strains as high as 10% are achieved [4], Fe-Pd-based MSM alloys, which have been demonstrated to yield up to 5% strain in single crystals [5][6][7], are highly promising owing to their higher corrosion resistance, reduced brittleness and recently demonstrated biocompatibility [8]. Although macroscopic properties and processing of bulk Fe-Pd samples are rather well established, the latter are much less understood when miniaturized. In particular, phase formation and twin boundary mobility are severely affected by the presence of open surfaces, substrates, strain fields and lattice defects-which on the one hand reveal an additional complication, but also bear the potential for optimization and new applications [9]. In fact, as recently shown for the complementary Ni-Mn-Ga system, maximum strains are feasible not only in single crystals, but also in porous polycrystals (i.e. in the presence of sufficient surfaces to relieve constraints) [10]. This hints at the high potential of appropriately processed polycrystalline foils based, for example, on the melt spinning [11][12][13][14] or splat quenching [15] techniques to achieve the desired face-centered tetragonal (fct) martensitic phase by a rapid quench of the austenitic face-centered cubic (fcc) lattice. These foils present an economical alternative to freestanding single crystalline films that can be grown, for example, by molecular beam epitaxy [9] and subsequently have to be lifted off the substrate [16].The MSM effect is based on a magnetic-field-induced reorientation of martensite variants, which is known to occur via twin boundary motion once the equivalent magnetic stresses overcome the twinning stress, σ t [17]. For high enough magnetic fields the maximum attainable equivalent magnetic stresses are limited by the magnetic anisotropy, K 1 , as it prevents rotation of the magnetic moments. That is, the maximum tolerable twinning stress is given by σ t < K 1 / 0 , where 0 denotes the maximum theoretical strain given solely by the lattice geometry of the martensite. On the microscopic scale, it is well established that reorientation of martensite New Journal of Physics 13 (2011) 063034 (http://www.njp.org/)
