Reversible Modification of Ferromagnetism through Electrically Controlled Morphology

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.