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Register a new userA dynamical magnetic field accompanying the motion of ferroelectric domain walls
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Added by
Dominik Maximilian Juraschek
Publication date
2019
fields
Physics
and research's language is
English
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The recently proposed dynamical multiferroic effect describes the generation of magnetization from temporally varying electric polarization. Here, we show that the effect can lead to a magnetic field at moving ferroelectric domain walls, where the rearrangement of ions corresponds to a rotation of ferroelectric polarization in time. We develop an expression for the dynamical magnetic field, and calculate the relevant parameters for the example of 90$^circ$ and 180$^circ$ domain walls in BaTiO$_3$ using a combination of density functional theory and phenomenological modeling. We find that the magnetic field reaches the order of several $mu$T at the center of the wall, and we propose two experiments to measure the effect with nitrogen-vacancy center magnetometry.
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We investigate magnetic domain wall (MDW) dynamics induced by applied electric fields in ferromagnetic-ferroelectric thin-film heterostructures. In contrast to conventional driving mechanisms where MDW motion is induced directly by magnetic fields or electric currents, MDW motion arises here as a result of strong pinning of MDWs onto ferroelectric domain walls (FDWs) via local strain coupling. By performing extensive micromagnetic simulations, we find several dynamical regimes, including instabilities such as spin wave emission and complex transformations of the MDW structure. In all cases, the time-averaged MDW velocity equals that of the FDW, indicating the absence of Walker breakdown.
The ease with which domain walls (DWs) in ferroelectric materials can be written and erased provides a versatile way to dynamically modulate heat fluxes. In this work we evaluate the thermal boundary resistance (TBR) of 180$^{circ}$ DWs in prototype ferroelectric perovskite PbTiO$_3$ within the numerical formalisms of nonequilibrium molecular dynamics and nonequilibrium Greens functions. An excellent agreement is obtained for the TBR of an isolated DW derived from both approaches, which reveals the harmonic character of the phonon-DW scattering mechanism. The thermal resistance of the ferroelectric material is shown to increase up to around 20%, in the system sizes here considered, due to the presence of a single DW, and larger resistances can be attained by incorporation of more DWs along the path of thermal flux. These results, obtained at device operation temperatures, prove the viability of an electrically actuated phononic switch based on ferroelectric DWs.
Magnetoelectric coupling in ferromagnet/multiferroic systems is often manifested in the exchange bias effect, which may have combined contributions from multiple sources, such as domain walls, chemical defects or strain. In this study we magnetically fingerprint the coupling behavior of CoFe grown on epitaxial BiFeO3 (BFO) thin films by magnetometry and first-order-reversal-curves (FORC). The contribution to exchange bias from 71{deg}, 109{deg} and charged ferroelectric domain walls (DWs) was elucidated by the FORC distribution. CoFe samples grown on BFO with 71{deg} DWs only exhibit an enhancement of the coercivity, but little exchange bias. Samples grown on BFO with 109{deg} DWs and mosaic DWs exhibit a much larger exchange bias, with the main enhancement attributed to 109{deg} and charged DWs. Based on the Malozemoff random field model, a varying-anisotropy model is proposed to account for the exchange bias enhancement. This work sheds light on the relationship between the exchange bias effect of the CoFe/BFO heterointerface and the ferroelectric DWs, and provides a path for multiferroic device analysis and design.
We report several procedures for the robust nucleation of magnetic domain walls in cylindrical permalloy nanowires. Specific features of the magnetic force microscopy contrast of such soft wires are discussed, with a view to avoid the misinterpretation of the magnetization states. The domain walls could be moved under quasistatic magnetic fields in the range 0.1--10 mT.
Ferroelectric domain walls represent multifunctional 2D-elements with great potential for novel device paradigms at the nanoscale. Improper ferroelectrics display particularly promising types of domain walls, which, due to their unique robustness, are the ideal template for imposing specific electronic behavior. Chemical doping, for instance, induces p- or n-type characteristics and electric fields reversibly switch between resistive and conductive domain-wall states. Here, we demonstrate diode-like conversion of alternating-current (AC) into direct-current (DC) output based on neutral 180$^{circ}$ domain walls in improper ferroelectric ErMnO$_3$. By combining scanning probe and dielectric spectroscopy, we show that the rectification occurs for frequencies at which the domain walls are fixed to their equilibrium position. The practical frequency regime and magnitude of the output is controlled by the bulk conductivity. Using density functional theory we attribute the transport behavior at the neutral walls to an accumulation of oxygen defects. Our study reveals domain walls acting as 2D half-wave rectifiers, extending domain-wall-based nanoelectronic applications into the realm of AC technology.
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