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The change in length of a ferromagnetic iron rod when magnetized was observed by J Joule in 1842 and is the first observation of the magnetostriction effect. The inverse effect—magnetoelasticity—was observed a few years later in 1865 by E Villari when looking at the magnetic susceptibility changes under stress in a ferromagnetic material. In the context of this special issue, we may define the magnetoelastic effect (or inverse magnetostriction) as the change of any magnetic property under mechanical deformation (strain). In a broader sense and beyond the scope of this collection, magnetoelasticity could be generalized as the mutual interconnection of magnetic and mechanical properties.
Although magnetoelasticity has been under investigation for a long time, recently we have seen a strong rise of interest in the field, often triggered by the promise of an alternative control of magnetization, without involving electrical currents, and at the nanoscale. For instance, in multiferroic heterostructures, ferroelectric and magnetic orders can be efficiently coupled through strain. In Spintronics devices, strain can be used as an additional degree of freedom or as a knob to reversibly adjust magnetic properties. The field of 'Straintronics' is emerging and we note that strain tuning of functionalities is not limited to magnetic ones.
In this special topic, we find an interesting collection of different methods and properties addressed, that reflect the diversity and the applied character of the field today. On the one hand, strain can be experimentally generated by a number of different approaches: for example, Finizio and coauthors use mechanical force (gas pressure) bending of a thin membrane [1]; Shepley and coautors a piezoelectric transducer [2] and Foerster and coauthors a piezoelectric substrate [3], both controlled by voltage signals. Kuszewski and coauthors create dynamical strain from a surface acoustic wave (SAW) [4]; Lauzier and coauthors employ the temperature driven structural phase transition of underlaying VO2 [5].
A similar variety is found in the targeted properties and magnetic systems addressed: Material parameters of in-plane magnetized thin films are modified (Ni, Lauzier et al [5], Co, Foerster et al [3]), while Duquesne and coautors propose a new method to determine those from experiment measuring the dynamic response to strain changes [6]. Strain-driven switching of magnetization is demonstrated by Kuszewski et al [4] in (Ga,Mn)As and treated in simulations for microstructures by Abeed and coauthors [7], who show not only that an optimal strain exists (more is not always better) but also that material defects can have a large influence. Finizio et al [1] observe an unexpected strong change in the vortex gyration frequency of CoFeB elements under isotropic strain, while Shepley et al [2] measure domain wall creep velocities in perpendicular magnetized Pt/Co/Ir and correlate them with the domain wall energy.
The presented work advances the field by adding predictive power (Sheply et al [2], Abeed et al [7]), developing new methods (Duquesne et al [6]) and reporting unexpected phenomena (Finizio et al [1]), in a case related to an imperfection of the piezosubstrate (Foerster et al [3]). From the applied point of view, questions of reversibility (Lauzier et al [5]) and reliability (Abeed et al [7]) are addressed and the possibility for deterministic switching explored (Kuszewski et al [4]). Thus, in several cases not only advances are reported, but maybe equally important, potential problems on the way to realization are highlighted and analyzed.
We hope the reader enjoys this special issue collection and finds it a useful collection, or better said, a starting point. There are many more works in past and recent literature to be found.
We deeply appreciate the contribution and efforts of all authors and want to thank the Editor team at IOP Journal of Physics: Condensed matter for the exemplary collaboration in bringing this special issue to life.