Comment on "Ultralow magnetostrictive flexible ferromagnetic nanowires" by G. Muscas, P. E. Jönsson, I. G. Serrano, Ö. Vallin, and M. V. Kamalakar, Nanoscale, 2021, 13, 6043-6052.

In a recent paper (G. Muscas et al.),1 the magnetomechanical behavior of cobalt (Co) magnetic nanowire arrays on a polymeric substrate (polyethylene naphthalate (PEN)) under bending was measured by magneto-optical Kerr effect (MOKE) magnetometry in situ. The authors showed that the magnetomechanical effects were very small and assigned this result to a low effective magnetostriction coefficient due to the nanostructuring. In this comment, we show by numerical calculations that it is the ongoing/current stress distribution within the system that generates this effect. Indeed, the nanostructures being very rigid with respect to the compliant substrate, the strains are mainly concentrated in the substrate and less than 3% of the macroscopic stress is transmitted to the nanostructures.

A review on nanostructured thin films on flexible substrates: links between strains and magnetic properties.

This paper provides a topical review of work on systems based on magnetic nanostructured thin films on polymer substrates. This topic has indeed experienced a significant growth in the last ten years. Several studies show a strong potential of these systems for a number of applications requiring functionalities on non-planar surfaces. However, the deformations necessary for this type of applications are likely to modify their magnetic properties, and the relationships between strain fields, potential damages and functional properties must be well understood. This review focuses both on the development of techniques dedicated to this research, on the synthesis of the experimental results obtained over the last ten years and on the perspectives related to stretchable or flexible magnetoelectric systems. In particular, the article focuses on the links between magnetic behavior and the strain field developing during the whole history of these systems (elaboration, reversible and irreversible loading).

Origin of relationship between ferromagnetic response and damage in stretched systems.

This article presents a study whose purpose is to elucidate the damage effects in thin films on their magnetic response. Co40Fe40B20 and Ni80Fe20 films of different nanometric thicknesses were stretched by more than 10% and in situ probed by atomic force microscopy measurements to determine their irreversible mechanical behavior (multi-cracking, buckling). Once these phenomena have been well identified, magnetic behavior of these stretched systems has been studied by ferromagnetic resonance to measure resulting magnetic anisotropy and damping evolutions. All of these experimental studies show that the magnetic properties are mainly affected by the stresses generated during the damage but not by the local discontinuities induced by the numerous cracks and buckles. This is in particular confirmed by the almost zero sensitivity to the damage of the magnetic properties of Ni80Fe20 alloy which is known for its vanishing magnetostriction.

Setup for high-temperature surface Brillouin light scattering: Application to opaque thin films and coatings.

A setup combining surface Brillouin light scattering with a high-temperature chamber has been developed. The temperature of the sample is controlled with a Bühler HDK chamber for optical measurements (maximum temperature of 1600 °C), in controlled atmospheres or high vacuum (10-6 mbar). This setup allows the study of sound velocity of surface acoustic waves and of the elastic constants of opaque thin films and coatings in situ as a function of temperature from surface Brillouin light scattering, by analyzing the backscattered light from the sample at a fixed angle of incidence. In this paper, we will demonstrate the applications of this setup for metallic glass thin films devitrification study and evaluation of high temperature elastic properties of hard nitride coatings. This kind of study using surface acoustic waves is rare, in contrast to those made on transparent bulk materials.

Data on the impact of increasing the W amount on the mass density and compressive properties of Ni-W alloys processed by spark plasma sintering.

Bulk Ni-W alloys having composite-like microstructures are processed by spark plasma sintering (SPS) route of Ni and W powder blends as reported in a recent study of Sadat et al. (2016) (DOI of original article: doi:10.1016/j.matdes.2015.10.083) [1]. The present dataset deals with determination of mass density and evaluation of room temperature compressive mechanical properties as function of the amount of W (%wt. basis). The presented data concern: (i) measurement of the mass of each investigated Ni-W alloy which is subsequently used to compute the mass density of the alloy and (ii) the raw (stress (MPa) and strain ([Formula: see text])) data, which can be subsequently used for stress/ strain plots.

Laue-DIC: a new method for improved stress field measurements at the micrometer scale.

A better understanding of the effective mechanical behavior of polycrystalline materials requires an accurate knowledge of the behavior at a scale smaller than the grain size. The X-ray Laue microdiffraction technique available at beamline BM32 at the European Synchrotron Radiation Facility is ideally suited for probing elastic strains (and associated stresses) in deformed polycrystalline materials with a spatial resolution smaller than a micrometer. However, the standard technique used to evaluate local stresses from the distortion of Laue patterns lacks accuracy for many micromechanical applications, mostly due to (i) the fitting of Laue spots by analytical functions, and (ii) the necessary comparison of the measured pattern with the theoretical one from an unstrained reference specimen. In the present paper, a new method for the analysis of Laue images is presented. A Digital Image Correlation (DIC) technique, which is essentially insensitive to the shape of Laue spots, is applied to measure the relative distortion of Laue patterns acquired at two different positions on the specimen. The new method is tested on an in situ deformed Si single-crystal, for which the prescribed stress distribution has been calculated by finite-element analysis. It is shown that the new Laue-DIC method allows determination of local stresses with a strain resolution of the order of 10(-5).

Development of a synchrotron biaxial tensile device for in situ characterization of thin films mechanical response.

We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine working in the synchrotron environment for in situ diffraction characterization of thin polycrystalline films mechanical response. The machine has been designed to test compliant substrates coated by the studied films under controlled, applied strain field. Technological challenges comprise the sample design including fixation of the substrate ends, the related generation of a uniform strain field in the studied (central) volume, and the operations from the beamline pilot. Preliminary tests on 150 nm thick W films deposited onto polyimide cruciform substrates are presented. The obtained results for applied strains using x-ray diffraction and digital image correlation methods clearly show the full potentialities of this new setup.