Influence of Nonuniform Micron-Scale Strain Distributions on the Electrical Reorientation of Magnetic Microstructures in a Composite Multiferroic Heterostructure

Abstract

Composite multiferroic systems, consisting of a piezoelectric substrate coupled with a ferromagnetic thin film, are of great interest from a technological point of view because they offer a path toward the development of ultralow power magnetoelectric devices. The key aspect of those systems is the possibility to control magnetization via an electric field, relying on the magneto-elastic coupling at the interface between the piezoelectric and the ferromagnetic components. Accordingly, a direct measurement of both the electrically induced magnetic behavior and of the piezo-strain driving such behavior is crucial for better understanding and further developing these materials systems. In this work, we measure and characterize the micron-scale strain and magnetic response, as a function of an applied electric field, in a composite multiferroic system composed of 1 and 2 μm squares of Ni fabricated on a prepoled [Pb(MgNb)O]-[PbTiO] (PMN-PT) single crystal substrate by X-ray microdiffraction and X-ray photoemission electron microscopy, respectively. These two complementary measurements of the same area on the sample indicate the presence of a nonuniform strain which strongly influences the reorientation of the magnetic state within identical Ni microstructures along the surface of the sample. Micromagnetic simulations confirm these experimental observations. This study emphasizes the critical importance of surface and interface engineering on the micron-scale in composite multiferroic structures and introduces a robust method to characterize future devices on these length scales.

Shear-strain-mediated magnetoelectric effects revealed by imaging

“…These extrema in magnetization are consistent with the expected 25 extrema in macroscopic strain (Fig. S4b, Supplementary Note 3), which have been hitherto understood to drive 90 rotations of a global magnetic easy axis 25,26,29,35,47,49,51 . The minima in M y correspond to a ~50% change of magnetization, and a peak ME coupling coefficient of (Fig.…”

“…However, if the out-of-plane component of polarization is electrically switched on and off then the in-plane component is necessarily modified (71 and 109 switching), such that the resulting change of in-plane strain permits non-volatile ME effects 25,26 . In practice, the global magnetic easy axis has been reported to undergo electrically driven 90 rotations 25,26,29,35,47,49,51 , consistent with a dominant component of normal strain along y  [01 ̅ 1] c (ref. 48).…”

“…One of the main goals in the study of magnetoelectrics is the electrical control of magnetism [1][2][3][4][5] . This has been previously demonstrated using bulk multiferroic materials [6][7][8][9][10] ; strained multiferroic composites 11 or multilayers 12 ; ferromagnetic films in which a gate controls semiconductor carrier density [13][14][15][16] or interfacial electronic structure [17][18][19] ; ferromagnetic films to which a magnetoelectric (ME) material imparts exchange bias 20 ; and ferromagnetic films to which a ferroelectric material imparts strain [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] , charge [36][37][38][39] and/or exchange bias [37][38][39] . Proposals for electric-write magnetic-read data-storage devices [40][41][42] focus on patterned ferromagnetic films that experience strain or exchange bias from ferroelectrics that are typica...…”

“…Therefore PMN-PT is widely exploited in ME heterostructures 22,26,28,29,32,34,35,46,47 , and more generally in commercial electromechanical devices such as transducers and actuators.…”

Full voltage manipulation of the resistance of a magnetic tunnel junction

“…Much effort has been dedicated to developing electrical approaches to manipulating MTJs, such as using electric field-modified coercivity (11) or magnetization precession (12) with the assistance of a mag netic field and using ferroelectric materials as the barrier layer with cryogenic operation temperature (13)(14)(15). The manipulation of magnetization in nanomagnets by voltage has been realized in ferromagnetic/ferroelectric multiferroic heterostructures (16)(17)(18), which is most effectively applied to manipulate MTJs with voltage instead of magnetic field or current. Therefore, integrating spintronics and multiferroics is emerging as a promising strategy for memory and logic (19) and presents a new opportunity for the energyefficient operation of MTJs, the key elements in spintronics.…”