Artificial Single Variant Martensite in Freestanding Fe<sub>70</sub>Pd<sub>30</sub>Films Obtained by Coherent Epitaxial Growth

Bechtold, Christoph; Buschbeck, J.; Lotnyk, Andriy; Erkartal, Burak; Hamann, Sven; Zamponi, Christiane; Schultz, L.; Ludwig, Alfred; Kienle, Lorenz; Fähler, S.; Quandt, Eckhard

doi:10.1002/adma.201000599

Cited by 20 publications

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“…The substrate defines different in-plane lattice constants, which allowed varying the tetragonal distortion within the Bain transformation path. In the thickness range from 50 nm up to 2 µm no relaxation was observed [8]. In the present work, we introduce Cu as a new substrate, which induces a tetragonal distortion of c/a = 1.09 within the Fe 70 Pd 30 filma value well beyond the Bain transformation path.…”

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Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

et al. 2011

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We exploit the intrinsic structural instability of the Fe(70)Pd(30) magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic, and ferroelectric materials.

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Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

et al. 2011

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“…This type of application also requires a high K and benefits from high J S and T C . In contrast to MSM microactuators, which require a release from the substrate [12] this is not necessary for recording applications. This paper is arranged as follows: After a short description of sample preparation and methods used for analysis we characterise in detail the structure of the epitaxial films.…”

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confidence: 99%

“…This reduces the driving force for the transformation and all associated relaxation processes and is thus favourable for strained epitaxial growth. Indeed, to avoid unfavourable relaxation mechanism like (111) fcc deformation twinning[37], very low deposition rates of 0.024 nm s -1 were required for epitaxial growth of binary Fe 70 Pd 30 films[12]. The present Fe-Pd-Cu films, however, were grown with a deposition rate one order of magnitude higher (0.3 nm s -1 ).…”

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Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

et al. 2012

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Strained epitaxial growth provides the opportunity to understand the dependence of intrinsic and extrinsic properties of functional materials at frozen intermediate stages of a phase transformation. In this study, a combination of thin film experiments and firstprinciples calculations yields the binding energy and magnetic properties of tetragonal Fe 70 Pd 30-x Cu x ferromagnetic shape memory thin films with x = 0, 3, 7 and structures ranging from bcc to beyond fcc (1.07 < c/a bct < 1.57).We find that Cu enhances the quality of epitaxial growth, while spontaneous polarisation and Curie temperature are only moderately lowered as expected from our calculations. Beyond c/a bct > 1.41 the samples undergo structural relaxations through adaptive nanotwinning. For all tetragonal structures, we observe a significant increase of the magnetocrystalline anisotropy constant K 1 , which reaches a maximum of K 1 ≈ -2.4*10 5 Jm -3 at room temperature around c/a bct = 1.33 and is thus even larger than for binary Fe 70 Pd 30 and the prototype Ni-Mn-Ga magnetic shape memory system. Since K 1 represents the driving force for variant reorientation in magnetic shape memory systems, we conclude that Fe-Pd-Cu alloys offer a promising route towards microactuators applications with significantly improved work output. Contents 1. Introduction 2. Experimental and theoretical methods 3. Structure and epitaxial relationship 4. Remanence, coercivity and saturation field 5. Change of Curie temperature and spontaneous polarisation 6. Change of magnetocrystalline anisotropy energy 7. Conclusions Acknowledgments References 1. Introduction Due to huge strains up to 10% [1] magnetic shape memory (MSM) alloys are of particular interest for microactuators [2]. Most research on bulk and thin films focuses on the Ni-Mn-Ga prototype system [3], but in particular for microsystems Fe 70 Pd 30 as the second system discovered [4] shows several advantages. While in the Ni-Mn-Ga system oxidation can result in functional degradation [5] the high content of the noble element Pd in Fe-Pd makes this MSM alloy even biocompatible [6]. Spontaneous magnetic polarisation J S and Curie temperature T C are considerably higher [7,8] compared to Ni-Mn-Ga. Whereas the high material cost hinder bulk applications of Fe-Pd, microsystems require only small masses of active material, which makes the material costs negligible compared to the increased process costs of film preparation.In this paper we quantify the influence of Cu alloying on the magnetic properties of Fe 70 Pd 30-x Cu x . Recent combinatorial experiments revealed that Cu can substantially increase the martensitic transformation temperature [9] which marks the upper limit of the working range for MSM applications. After a thorough crystallographic characterisation of the films we will focus on magnetic aspects, in particular on the magnetocrystalline anisotropy energy.As an intrinsic material property, the anisotropy constant K represents the maximum energy density which can be supplied by an external magnetic fi...

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“…Close to this bcc ground state, Fe 70 Pd 30 films on Au buffer grow epitaxial up to a thickness of 1.2 µm [31]. In case of this Au buffer, no bcc-type twinning was observed.…”

Section: Bcc Deformation/growth Twinsmentioning

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Twinning Phenomena along and beyond the Bain Path

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et al. 2013

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Twinning is a phenomenon that occurs, e.g., during deformation, martensitic transformation and film growth. The present study shows that the crystallography of twinning can be described by two twinning modes along the complete Bain transformation path and beyond connecting body-centered and face-centered cubic structures. To probe this concept, we used strained epitaxial films of the Fe-Pd magnetic shape memory system. As the substrate acts as an absolute reference frame, we could show by pole figure measurements that all observed twinning can be a body-centered and face-centered cubic twinning mode. This continuously transforms towards identity when approaching the complementary structure.

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Artificial Single Variant Martensite in Freestanding Fe₇₀Pd₃₀Films Obtained by Coherent Epitaxial Growth

Cited by 20 publications

References 18 publications

Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

Twinning Phenomena along and beyond the Bain Path

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Artificial Single Variant Martensite in Freestanding Fe70Pd30Films Obtained by Coherent Epitaxial Growth

Cited by 20 publications

References 18 publications

Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

Magnetic Nanostructures by Adaptive Twinning in Strained Epitaxial Films

Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu

Twinning Phenomena along and beyond the Bain Path

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Artificial Single Variant Martensite in Freestanding Fe₇₀Pd₃₀Films Obtained by Coherent Epitaxial Growth