Nanoscale magneto-structural coupling in as-deposited and freestanding single-crystalline Fe₇Pd₃ferromagnetic shape memory alloy thin films

Abstract

Ferromagnetic shape memory alloys are characterized by strong magneto-mechanical coupling occurring at the atomic scale causing large magnetically inducible strains at the macroscopic level. Employing combined atomic and magnetic force microscopy studies at variable temperature, we systematically explore the relation between the magnetic domain pattern and the underlying structure for as-deposited and freestanding single-crystalline Fe7Pd3 thin films across the martensite–austenite transition. We find experimental evidence that magnetic domain appearance is strongly affected by the presence and absence of nanotwinning. While the martensite–austenite transition upon temperature variation of as-deposited films is clearly reflected in topography by the presence and absence of a characteristic surface corrugation pattern, the magnetic domain pattern is hardly affected. These findings are discussed considering the impact of significant thermal stresses arising in the austenite phase. Freestanding martensitic films reveal a hierarchical structure of micro- and nanotwinning. The associated domain organization appears more complex, since the dominance of magnetic energy contributors alters within this length scale regime.

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3ferromagnetic shape memory alloy thin films

“…The unirradiated sample shows a well-defined and ordered MFM pattern consisting of alternating dark and bright stripes with a width in the range of 300 nm. This finding, which we have reported previously [34], indicates significant out-of-plane contributions to the magnetization, which, at first glance, is at odds with the cubic symmetry of the single crystalline austenite Fe 7 Pd 3 film, as in-plane alignment of the magnetic moments is expected to reduce stray fields. As we demonstrated previously [34], however, a strong anisotropy caused by film stresses can explain this scenario, even quantitatively.…”

“…This finding, which we have reported previously [34], indicates significant out-of-plane contributions to the magnetization, which, at first glance, is at odds with the cubic symmetry of the single crystalline austenite Fe 7 Pd 3 film, as in-plane alignment of the magnetic moments is expected to reduce stray fields. As we demonstrated previously [34], however, a strong anisotropy caused by film stresses can explain this scenario, even quantitatively. Upon transformation to martensite, the two longer axes of the tetragonal unit cell constitute the easy axes of magnetization [32].…”

Behaviors of Ferromagnetic Shape Memory Alloy Ni–Mn–Ga Under Incomplete Magneto‐Mechanical Loading–Unloading Cycles

“…[10,11] Among the known FSMAs, Ni-Mn-Ga alloys are the most widely explored due to their low twinning stress and sufficiently high magnetocrystalline anisotropy energy. [13,14] Although many investigations have been reported on several aspects of FSMAs including development of new alloys, [15,16] thin films, [17] and surface characteristics, [18,19] it seems that more studies are required on their behavior under incomplete loadingunloading cycles. [12] Therefore, one of the main research goals is to produce FSMA in which a large MFIS can be induced at high stress levels for the purpose of maximizing the work output.…”

Exploring Coupled Martensitic and Order–Disorder Phase Transitions in Fe7Pd3 Shape Memory Alloys Equilibrated Along the Bain Path: An Embedded Atom Method and Ab Initio Based Monte Carlo Study

“…[9,10] This alloy still constitutes one of the most prominent representatives of this class due to its ferromagnetic shape memory effect (FSME) and magneto-caloric effect. [4,[11][12][13] When describing the Fe 7 Pd 3 alloy, however, there are still ambiguities in regard to influences on phase stability and consequently phase transitions. In the case of disordered Fe 7 Pd 3 four metastable phases are reported: the high temperature austenite phase, crystallographically assigned to the face centered cubic (fcc) lattice, as well as three lower temperature martensite phases, which are distinguished by the degree of tetragonal distortion compared to the fcc/austenite phase.…”