Self-patterning of epitaxial Ni–Mn–Ga/MgO(001) thin films

Abstract

In this work, a detailed report on the growth of elongated bar-like crystallites with a definite crystallographic orientation, forming a self-organized patterned surface layer, with a thickness of about 100 nm, onto 900 nm thick ferromagnetic shape memory alloy Ni-Mn-Ga films epitaxially grown on MgO(001) is presented. The phenomenon appears above a threshold of lattice mismatch (≈2%) between the film and substrate. The structural, magnetic and transformation properties of such films are described and analyzed. Particularly, the different magnetic states of the two film layers are discerned by ferromagnetic resonance. The feasibility of creating a ferromagnetic shape memory alloy with a nanoscale self-patterned surface, during the very same process of film deposition, can be interesting for potential applications where control of the surface architecture would be needed.

Properties and Decomposition of Heusler Alloys

“…If the e / a ‐ratio is increased by substitution of Ga by Mn, very stable alloys are achieved. Other interesting aspects like large precipitates, “self‐patterning”, and the influence of vacancies on modulated and non‐modulated phases were investigated . This short discussion of properties of nonstoichiometric Heusler alloys is by far not complete, but, it gives an impression on the rich properties of functional magnetic Heusler alloys.…”

“…Other interesting aspects like large precipitates," self-patterning", and the influence of vacancies on modulated and non-modulated phases were investigated. [79][80][81] This short discussion of properties of nonstoichiometric Heusler alloys is by far not complete,b ut, it gives an impression on the rich properties of functional magnetic Heusler alloys.W er emind the reader of the shift of the martensitic transformation temperaturef or the rapidly quenched alloys,w hich is proportional to the square of the external magneticf ield and which was already predicted by Ghatake tal. [38,39] Thea ssociated so-calledk inetic arrest phenomenon still requires further simulation work for full understanding.…”

Probing Structural and Magnetic Instabilities and Hysteresis in Heuslers by Density Functional Theory Calculations

“…If the ratio e / a is increased by substitution of Ga by Mn, very stable alloys are achieved. Other interesting aspects like large precipitates, “self‐patterning”, influence of vacancies on modulated and non‐modulated phases were investigated . This short list of discussing properties of non‐stoichiometric Heusler alloys is by far not complete, but, it gives an impression on the rich properties of functional magnetic Heusler alloys.…”

Microstructural evolution and magnetic properties of binder jet additive manufactured Ni-Mn-Ga magnetic shape memory alloy foam

“…In general, polycrystalline bulk Ni-Mn-Ga alloysare brittle, costly and display moderate MFIS due to high twinning stresses limiting their practical applications. Therefore, various processing methods have been developed to modify microstructure and mechanical properties of the Ni-Mn-Ga alloys such as melt spinning [13], spark plasma sintering [14,15], composites [16][17][18][19]and thin films [20][21][22]. Another alternative to reach high MFIS is to manufacture a porous structure to reduce internal constraints.…”

“…Another alternative to reach high MFIS is to manufacture a porous structure to reduce internal constraints. Chmielus et alpresented a Ni-Mn-Ga open-pore foam with a monomodal [22] and bimodal [23]pore size of 76% volume fraction and an MFIS of 0.12%.Müllneret al [25] proposed that the main mechanism of reducing internal and external constraints via porosity and foam architecture is based on the reduction in twin-twin and twingrain boundary interactions.It is expected that high saturation magnetization is favorable to the MFIS [9]. The saturation magnetization of Ni-Mn-Ga single crystals may vary between 50 and 70 Am 2 /kg [26,27] and after ball milling, it may drop to 15-25 Am 2 /kg depending on the time and milling energy [28].…”