The direct current (d.c.) conductivity and emergent functionalities at ferroelectric domain walls are closely linked to the local polarization charges. Depending on the charge state, the walls can exhibit unusual d.c. conduction ranging from insulating to metallic-like, which is leveraged in domain-wall-based memory, multi-level data storage, and synaptic devices. In contrast to the functional d.c. behaviors at charged walls, their response to alternating currents (a.c.) remains to be resolved. Here, we reveal a.c. characteristics at positively and negatively charged walls in ErMnO3, distinctly different from the response of the surrounding domains. By combining voltage-dependent spectroscopic measurements on macroscopic and local scales, we demonstrate a pronounced non-linear response at the electrode-wall junction, which correlates with the domain-wall charge state. The dependence on the a.c. drive voltage enables reversible switching between uni-and bipolar output signals, providing conceptually new opportunities for the application of charged walls as functional nanoelements in a.c. circuitry.
Using strain, i.e. subtle changes in lattice constant in a thin film induced by the underlying substrate, opens up intriguing new ways to control material properties. We present a study of the effects of strain on structural and ferromagnetic properties of (1 1 1)-oriented LaSrMnO epitaxial thin films grown on NdGaO, SrTiO, and DyScO substrates. (The subscript pc denotes the pseudo-cubic symmetry.) The results show that LaSrMnO assumes a monoclinic unit cell on NdGaO and DyScO and a rhombohedral unit cell on SrTiO. For LaSrMnO on NdGaO and DyScO a uniaxial magnetic anisotropy is found, while LaSrMnO on SrTiO is magnetically isotropic. The Néel model is used to explain the anisotropy of the thin films on NdGaO and SrTiO, however, for LaSrMnO on DyScO the effect of octahedral rotations needs to be included through the single ion model. Through examination of the Curie temperature of the strained films we suggest that (1 1 1)-strain has a different effect on the Jahn-Teller splitting of e and t electron levels than what is seen in (0 0 1)-oriented LaSrMnO thin films.
Topologically nontrivial
spin textures, such as skyrmions and dislocations,
display emergent electrodynamics and can be moved by spin currents
over macroscopic distances. These unique properties and their nanoscale
size make them excellent candidates for the development of next-generation
race-track memory and unconventional computing. A major challenge
for these applications and the investigation of nanoscale magnetic
structures in general is the realization of suitable detection schemes.
We study magnetic disclinations, dislocations, and domain walls in
FeGe and reveal pronounced responses that distinguish them from the
helimagnetic background. A combination of magnetic force microscopy
(MFM) and micromagnetic simulations links the response to the local
magnetic susceptibility, that is, characteristic changes in the spin
texture driven by the MFM tip. On the basis of the findings, which
we explain using nonlinear response theory, we propose a read-out
scheme using superconducting microcoils, presenting an innovative
approach for detecting topological spin textures and domain walls
in device-relevant geometries.
The magnetic anisotropy of films of La0.7Sr0.3MnO3 grown on vicinal (111)-oriented SrTiO3 substrates are investigated. For temperatures above the tetragonal -cubic structural phase transition temperature of the substrate, a step edge induced uniaxial magnetic anisotropy is found at remanence, with a thickness-driven change in easy axis direction, from perpendicular to the step edges to parallel to the step edges with increasing thickness. The anisotropy constant for the investigated (111)-oriented samples is of the same magnitude as for previously reported (001)-oriented samples. The data is discussed in the framework of in-plane rotations of the oxygen octahedra resulting in a uniaxial anisotropy. Furthermore, the magnetic anisotropy is sensitive to the structural phase transition at 105K of the substrate, and the anisotropy constant increases drastically as the temperature is lowered below 105K.
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