Reversible Modification of Ferromagnetism through Electrically Controlled Morphology

Abstract

Converse magnetoelectric coupling in artificial multiferroics is generally modeled through three possible mechanisms: charge transfer, strain mediated effects or ion migration. Here the role played by electrically controlled morphological modifications on the ferromagnetic response of a multiferroic heterostructure, specifically FexMn1−x ferromagnetic films on piezoferroelectric PMN‐PT [001] substrates, is discussed. The substrates present, in correspondence to electrical switching, fully reversible morphological changes at the surface, to which correspond reproducible modifications of the ferromagnetic response of the FexMn1−x films. Topographic analysis by atomic force microscopy shows the formation of surface cracks (up to 100 nm in height) upon application of a sufficiently high positive electric field (up to 6 kV cm−1). The cracks disappear after application of negative electric field of the same magnitude. Correspondingly, in operando X‐ray magnetic circular dichroic spectroscopy at Fe edge in FexMn1−x layers and micro‐MOKE measurements show local variations in the intensity of the dichroic signal and in the magnetic anisotropy as a function of the electrically driven morphological state. This morphologic parameter, rarely explored in literature, directly affects the ferromagnetic response of the system. Its proof of electrically reversible modification of the magnetic response adds a new possibility in the design of electrically controlled magnetic devices.

Interplay between morphology and magnetoelectric coupling in Fe/PMN-PT multiferroic heterostructures studied by microscopy techniques

“…In the (001) case instead, the cracks are dense, highly irregular, and their shape varies drastically on the 100-μm scale. Therefore, magnetoelectric effects vary substantially on the same scale: opposite effects on M in response to the same electric polarization were observed, according to the mesoscopic area 344 probed and the crack pattern [38]. Another difference lies 345 in the relationship between cracks and easy axis.…”

“…With a field of view of 50 μm, the imaged area is comparable with the one probed by XMCD measurements. We can therefore use PEEM to have a "spatially resolved insight" of the previously reported data [38]. Two-dimensional (2D) maps of the magnetization were obtained at zero electric bias, before and after switching the polarization between P up and P down in situ on a demagnetized sample.…”

“…heterostructures [38]. Both reports show that the surface cracking of the substrate breaks the interfacing metallic film when switching the polarization out of plane.…”

“…Cracked and smooth 120 morphologies correspond hence to opposite orientations of 121 P (from here on, P up and P down , respectively). The change is 122 evident at the coercive electric field [E C ≈ 1.5 kV/cm, see 123 although terraces up to 100 nm high were observed [38].…”

CLeANFIT – Contact‐Less Axial Nearfield‐Based Fluorescence Imaging Topography: A Method for 3D Micro‐ and Nanotopography Characterization

“…[ 66–70 ] Targeting nanoinkjet printing, various characterization techniques have been proposed for the observation and analysis of the involved nano‐ to picoliter droplets. For morphological studies, both in the dried and the liquid states, confocal microscopy, [ 71 ] SEM, [ 72 ] AFM, [ 70 ] contact profilometry, [ 73 ] and interferometry [ 63 ] have been tested. However, all these methods are either limited by their axial resolution, or by damages on the material surface due to direct contact of the sample with a tip, preventing in situ analysis.…”