Magnetically induced reorientation of martensite variants in constrained epitaxial Ni–Mn–Ga films grown on MgO(001)

Thomas, Michael F.; Heczko, Oleg; Buschbeck, J.; Rößler, U.; McCord, Jeffrey; Scheerbaum, N.; Schultz, L.; Fähler, S.

doi:10.1088/1367-2630/10/2/023040

Cited by 112 publications

(128 citation statements)

References 32 publications

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“…This is of advantage as the martensitic microstructure of epitaxial films has been examined in detail. [18][19][20][21] All measurements have been performed in the as-deposited state at room temperature, which is below the ferroelastic and ferromagnetic order temperature. We did not apply an external magnetic field during the 4 measurements.…”

Section: Introductionmentioning

confidence: 99%

Magnetic domain pattern in hierarchically twinned epitaxial Ni–Mn–Ga films

Diestel

Neu

Backen

et al. 2013

J. Phys.: Condens. Matter

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Magnetic shape memory alloys exhibit a hierarchically twinned microstructure, which has been well examined in epitaxial Ni-Mn-Ga films. Here we analyze consequences of this "twin within twins" microstructure on the magnetic domain pattern. Atomic and magnetic force microscopy are used to probe the correlation between the martensitic microstructure and magnetic domains. We examine consequences of different twin boundary orientations with respect to the substrate normal as well as variant boundaries between differently aligned twinned laminates. A detailed micromagnetic analysis is given which describes the influence of the finite film thickness on the formation of magnetic band domains in these multiferroic materials.

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Section: Introductionmentioning

confidence: 99%

Magnetic domain pattern in hierarchically twinned epitaxial Ni–Mn–Ga films

Diestel

Neu

Backen

et al. 2013

J. Phys.: Condens. Matter

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“…[10][11][12][13] It is remarkable that the reported values of the switching field are similar despite different growth techniques, sample orientations, and used substrates. In the following, we will show that this behavior can be explained on the basis of the model, which assumes the martensitic twin variant structure as fixed and only considers the magnetostatic interactions and the evolution of magnetic domains.…”

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confidence: 90%

“…[10][11][12][13] In analogy to bulk materials, this effect has also been identified as MIR of twin variants. However, a conclusive MIR model for thin films on a rigid substrate is still missing, owing to the fact that the substrate inhibits any macroscopic length change and thus hampers the magnetically induced change in the martensitic microstructure of an MSM film.…”

mentioning

confidence: 99%

“…10 This model is based on the fact that an orthorhombic structure allows three free parameters for the orientation of the unit cell. Hence, in an applied magnetic field, a reorientation of the unit cells is possible if the fraction of the a-variants (longest lattice constant) is reduced when the fraction of b-variants (medium lattice constant) increases and the fraction of c-variants (shortest lattice constant) is reduced at the same time.…”

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confidence: 99%

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Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

Laptev

Lebecki

Welker

et al. 2016

Applied Physics Letters

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We study the temperature dependent magnetization properties of (010)-oriented Ni-Mn-Ga epitaxial films on MgO(001) substrates. In the martensitic phase, we observe pronounced abrupt slope changes in the magnetization loops for all studied samples. Our experimental findings are discussed in conjunction with the micromagnetic simulations, revealing that the characteristic magnetization behavior is governed solely by the magnetization switching within the specific martensitic variant pattern, and no reorientation of twin variants is involved in the process. Our study emphasizes the important role of the magnetostatic interactions in the magnetization behavior of magnetic shape memory alloy thin films. Published by AIP Publishing.[http://dx.doi.org/10.1063/1.4963264] Magnetic shape memory (MSM) alloys exhibit a remarkable functional property to generate macroscopic strains upon exposure to a magnetic field of sufficient strength. 1,2 The strong coupling between the structural and magnetic degrees of freedom gives rise to the magnetically induced reorientation (MIR) of the twinned martensitic microstructure, resulting in a magnetic field-induced strain (MFIS). Strain values of up to 12% were reported for single crystals, 3-5 boosting the research interest especially in MSM thin films, which have a strong application potential in sensing and actuation systems. [6][7][8] In particular, the investigation of twin variant reorientation in epitaxial films has been the subject of several studies. However, the direct identification of the change of microstructure or the shape upon the application of external magnetic fields in thin films is a challenging task. Therefore, in analogy to bulk material studies, 9 magnetization measurements have been utilized in order to identify the MIR of twin variants. The reorientation of martensitic variants is linked to the reorientation of the easy magnetization axis, resulting in a strong change of the measured magnetization of the sample.A step-like increase in the magnetization has indeed been observed in constrained epitaxial thin films grown on different substrates. [10][11][12][13] In analogy to bulk materials, this effect has also been identified as MIR of twin variants. However, a conclusive MIR model for thin films on a rigid substrate is still missing, owing to the fact that the substrate inhibits any macroscopic length change and thus hampers the magnetically induced change in the martensitic microstructure of an MSM film.In this paper, we address the origin of steps in the magnetization loops of constrained epitaxial MSM films. We study the role of the martensitic microstructure and the magnetostatic interactions on the magnetization process of epitaxial Ni-Mn-Ga films on a rigid substrate. We employ temperature-dependent magnetization measurements and micromagnetic simulations to develop a model, which consistently explains the peculiar magnetization behavior.For this study, we use three epitaxial Ni-Mn-Ga film samples with different thicknesses (see Table I), prepared by DC m...

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“…This kind of morphology also been observed in other shape memory alloy system e.g. Ni-Mn-Ga. [33][34][35][36][37] The twinning in the films P3 and P4 at RT indicate the presence of a finely twinned room temperature martensite which could not be detected in RT x-ray diffraction studies, that are sensitive to the epitaxial lattice planes parallel to the substrate surface only. The observed morphologies are also evident in the SEM measurements.…”

Section: Microstructural Featuresmentioning

confidence: 99%

Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

Machavarapu

Jakob

2015

AIP Advances

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We report the effect of substrate temperature (TS) and Ar gas pressure (PD) on the martensitic transformations, magnetic and exchange bias (EB) properties in Heusler type Ni-Co-Mn-Sn epitaxial thin films. Martensitic transformation temperatures and EB fields at 5 K were found to increase with increasing TS. The observed maximum EB value of 320 Oe after field cooling in the film deposited at 650 ∘C is high among the values reported for Ni-Mn-Sn thin films which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AF) phases in the martensitic state. In the case of PD variation, with increase in PD, martensitic transformation temperatures were increased and a sharp transformation was observed in the film deposited at 0.06 mbar. Magnetization values at 5 K were higher for increasing PD. These observations are attributed to the compositional shift. EB effect is also present in these films. Microstructural features observed using atomic force microscopy (AFM) shows a fine twinning and reduced precipitation with increase in PD, which is also confirmed from the scanning electron microscopy (SEM) images. EB effects in both series were confirmed from the training effect. Target ageing effect has been observed in the films deposited before and after ninety days of time interval. This has been confirmed both on substrate temperature and Ar gas pressure variations.

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Magnetically induced reorientation of martensite variants in constrained epitaxial Ni–Mn–Ga films grown on MgO(001)

Cited by 112 publications

References 32 publications

Magnetic domain pattern in hierarchically twinned epitaxial Ni–Mn–Ga films

Magnetic domain pattern in hierarchically twinned epitaxial Ni–Mn–Ga films

Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

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