Interfacial coupling in multiferroic/ferromagnet heterostructures

Abstract

We report local probe investigations of the magnetic interaction between BiFeO 3 films and a ferromagnetic Co 0.9 Fe 0.1 layer. Within the constraints of intralayer exchange coupling in the Co 0.9 Fe 0.1 , the multiferroic imprint in the ferromagnet results in a collinear arrangement of the local magnetization and the in-plane BiFeO 3 ferroelectric polarization. The magnetic anisotropy is uniaxial, and an in-plane effective coupling field of order 10 mT is derived. Measurements as a function of multiferroic layer thickness show that the influence of the multiferroic layer on the magnetic layer becomes negligible for 3 nm thick BiFeO 3 films. We ascribe this breakdown in the exchange coupling to a weakening of the antiferromagnetic order in the ultrathin BiFeO 3 film based on our X-ray linear dichroism measurements. These observations are consistent with an interfacial exchange coupling between the CoFe moments and a canted antiferromagnetic moment in the BiFeO 3 .

Probing electric field control of magnetism using ferromagnetic resonance

“…1c) and the other with net IP magnetization antiparallel (blue/cyan striped region). The coexistence of parallel and antiparallel magnetization orientations, along with other measurements, demonstrates that the magnetic coupling to the BFO leads to a net uniaxial rather than unidirectional anisotropy in the CoFe layer 17 .…”

“…1a 17 . We image the magnetic structure of the CoFe layer at zero magnetic field using scanning electron microscopy with polarization analysis (SEMPA) 38 .…”

“…To understand the voltage-dependent FMR data, we consider a CoFe layer exchange coupled to the canted moments of a BFO layer within the two ferroelectric domains as shown in Fig. 3a [13][14][15][16][17] . The canted magnetic moment orientations (green and orange) in the two ferroelectric domains (red and blue, respectively) of the BFO thin film are perpendicular to each other 13 .…”

“…Multiferroic materials with simultaneous ferroelectricity and magnetism provide a pathway to achieving strong magnetoelectric coupling with efficient voltage control of magnetism, and compact and power-efficient electric field-tunable magnetic devices [1][2][3][4] . A variety of 'magnetoelectric-multiferroics' such as magnetic/ferroelectric [5][6][7][8][9][10][11][12] and magnetic/multiferroic [13][14][15][16][17] heterostructures have been investigated, which are providing pathways to novel electric field-tunable radio frequency (RF)/microwave signal processing devices 5 , magnetic field sensors 6 , MERAM devices 7 and voltagetunable magnetoresistance devices 8 .…”

“…The room temperature single-phase multiferroic, BiFeO 3 (BFO), has attracted a lot of recent research interest due to the coexistence of robust ferroelectricity (P) and antiferromagnetism (L) [13][14][15][16][17][29][30][31][32][33][34][35][36] and a weak canted magnetic moment (M C ). In bulk BFO, the weak moment results from the canting of the magnetic sublattices due to the Dzyaloshinskii-Moriya interaction 14 as predicted by the density functional theory 14 and confirmed experimentally 30,36 .…”