arXiv subjects

Kristina M. Holsgrove

Publications and source records attributed to Kristina M. Holsgrove.

4 recordsLinked to original sources

arXiv2026

Low-Field Ferroelectric Switching realised by Forced Harmonic Oscillation of Domain Walls

Conventionally, dc fields are used for switching dipole orientations in ferroelectrics. Such fields tilt the potential surface experienced by domain walls and thereby lower activation energies for their movement: escape from tilted potential wells is then realised by thermal excitation, allowing a "creep" process of pinning and depinning to develop. Borrowing ideas of domain wall resonance from the magnetic racetrack community, we show that ac fields, applied at the right frequency, can cause switching at much lower field magnitudes than dc ones (by factors of 4-5). Ferroelectric wall motion appears to be overdamped in the system studied (relaxor strontium barium niobate) and so the maximum in switching efficacy observed, at ~100 kHz, cannot be associated with resonant amplification, which needs an underdamped environment. Instead, in this high viscosity system, the frequency at which the maximum switching efficacy occurs seems to represent a compromise between the attempt frequency for wall depinning (which increases with frequency) and the extent to which energy is transferred to the wall within each field cycle (which decreases with frequency). Notwithstanding the absence of true resonance, the observation that ac excitation can dramatically reduce the bias levels needed for ferroelectric switching could still have significant ramifications for low energy memory technology.

cond-mat.mtrl-sci↗

arXiv2025

Direct Thermal Imaging of Domain Wall Hot Spots in LiNbO3

Ferroelectric domain wall devices offer a promising route to low-voltage, reconfigurable nanoelectronics by confining currents to nanoscale conducting interfaces within an insulating bulk. However, the potential for resistive heating and unregulated temperature increases due to domain wall conduction remains unexplored. Here, scanning thermal microscopy is employed to directly image hot spots in thin-film lithium niobate domain wall devices. Piezoresponse force microscopy shows that the hot spots correlate with nanodomain structure, and thermal mapping reveals surface temperature rises of ~20 K at most, levels that are unlikely to negatively affect device performance. This is due to the moderate electrical conductivity of domain walls, their voltage-tunable erasure, and distributed current pathways, which inherently limit power dissipation and peak temperatures. Finite element electrothermal modelling indicates that domain walls behave as pseudo-planar heat sources, distinct from the filament-based heating typically observed in resistive switching oxides. These findings highlight the potential for domain wall devices as an energy-efficient, thermally stable platform for emerging memory and logic applications.

cond-mat.mtrl-sci↗

arXiv2024

AFM-based Functional Tomography-To Mill or not to Mill, that is the Question!

The electrical response of ferroelectric domain walls is often influenced by their geometry underneath the sample surface. Tomographic imaging in these material systems has therefore become increasingly important for its ability to correlate the surface-level functional response with subsurface domain microstructure. In this context, AFM-based tomography emerges as a compelling choice because of its simplicity, high resolution and robust contrast mechanism. However, to date, the technique has been implemented in a limited number of ferroelectric materials, typically to depths of a few hundred nanometers or on relatively soft materials, resulting in an unclear understanding of its capabilities and limitations. In this work, AFM tomography is carried out in YbMnO3, mapping its complex domain microstructure up to a depth of around 1.8 um along with its current pathways. A model is presented, describing the impact of interconnected domain walls within the network, which act as current dividers and codetermine how currents distribute. Finally, challenges such as tip-blunting and subsurface amorphisation are identified through TEM studies, and strategies to address them are also put forward. This study highlights the potential of AFM tomography and could spur interest within the ferroics community for its use in the investigation of similar material systems.

cond-mat.mtrl-sci↗

arXiv2024

Spatially Resolved High Voltage Kelvin Probe Force Microcopy: A Novel Avenue for Examining Electrical Phenomena at Nanoscale

Kelvin probe microscopy (KPFM) is a well-established scanning probe technique, used to measure surface potential accurately; it has found extensive use in the study of a range of materials phenomena. In its conventional form, KPFM frustratingly precludes imaging samples or scenarios where large surface potential exists or large surface potential gradients are created outside the typical +/-10V window. If the potential regime measurable via KPFM could be expanded, to enable precise and reliable metrology, through a high voltage KPFM (HV-KPFM) adaptation, it could open up pathways towards a range of novel experiments, where the detection limit of regular KPFM has so far prevented the use of the technique. In this work, HV-KPFM has been realised and shown to be capable of measuring large surface potential and potential gradients with accuracy and precision. The technique has been employed to study a range of materials (positive temperature coefficient of resistivity ceramics, charge storage fluoropolymers and pyroelectrics) where accurate spatially resolved mapping of surface potential within high voltage regime facilitates novel physical insight. The results demonstrate that HV-KPFM can be used as an effective tool to fill in existing gaps in surface potential measurements while also opening routes for novel studies in materials physics.

cond-mat.mtrl-sci↗