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Register a new userNanoscale magnetization and current imaging using scanning-probe magneto-thermal microscopy
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Magnetic microscopy that combines nanoscale spatial resolution with picosecond scale temporal resolution uniquely enables direct observation of the spatiotemporal magnetic phenomena that are relevant to future high-speed, high-density magnetic storage and logic technologies. Magnetic microscopes that combine these metrics has been limited to facility-level instruments. To address this gap in lab-accessible spatiotemporal imaging, we develop a time-resolved near-field magnetic microscope based on magneto-thermal interactions. We demonstrate both magnetization and current density imaging modalities, each with spatial resolution that far surpasses the optical diffraction limit. In addition, we study the near-field and time-resolved characteristics of our signal and find that our instrument possesses a spatial resolution on the scale of 100 nm and a temporal resolution below 100 ps. Our results demonstrate an accessible and comparatively low-cost approach to nanoscale spatiotemporal magnetic microscopy in a table-top form to aid the science and technology of dynamic magnetic devices with complex spin textures.
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Scanning Thermal Microscopy (SThM) uses micromachined thermal sensors integrated in a force sensing cantilever with a nanoscale tip can be highly useful for exploration of thermal management of nanoscale semiconductor devices. As well as mapping of surface properties of related materials. Whereas SThM is capable to image externally generated heat with nanoscale resolution, its ability to map and measure thermal conductivity of materials has been mainly limited to polymers or similar materials possessing low thermal conductivity in the range from 0.1 to 1 W/mK, with lateral resolution on the order of 1 mum. In this paper we use linked experimental and theoretical approaches to analyse thermal performance and sensitivity of the micromachined SThM probes in order to expand their applicability to a broader range of nanostructures from polymers to semiconductors and metals. We develop physical models of interlinked thermal and electrical phenomena in these probes and then validate these models using experimental measurements of the real probes, which provided the basis for analysing SThM performance in exploration of nanostructures. Our study then highlights critical features of these probes, namely, the geometrical location of the thermal sensor with respect to the probe apex, thermal conductance of the probe to the support base, heat conduction to the surrounding gas, and the thermal conductivity of tip material adjacent to the apex. It is furthermore allows us to propose a novel design of the SThM probe that incorporates a carbon nanotube (CNT) or similar high thermal conductivity graphene sheet material positioned near the probe apex. The new sensor is predicted to provide spatial resolution to the thermal properties of nanostructures on the order of few tens of nm, as well as to expand the sensitivity of the SThM probe to materials with heat conductivity values up to 100-1000 W/mK.
The ability to experimentally map the three-dimensional structure and dynamics in bulk and patterned three-dimensional ferromagnets is essential both for understanding fundamental micromagnetic processes, as well as for investigating technologically-relevant micromagnets whose functions are connected to the presence and dynamics of fundamental micromagnetic structures, such as domain walls and vortices. Here, we demonstrate time-resolved magnetic laminography, a technique which offers access to the temporal evolution of a complex three-dimensional magnetic structure with nanoscale resolution. We image the dynamics of the complex three-dimensional magnetization state in a two-phase bulk magnet with a lateral spatial resolution of 50 nm, mapping the transition between domain wall precession and the dynamics of a uniform magnetic domain that is attributed to variations in the magnetization state across the phase boundary. The capability to probe three-dimensional magnetic structures with temporal resolution paves the way for the experimental investigation of novel functionalities arising from dynamic phenomena in bulk and three-dimensional patterned nanomagnets.
Scanning probe microscopy is one of the most versatile windows into the nanoworld, providing imaging access to a variety of sample properties, depending on the probe employed. Tunneling probes map electronic properties of samples, magnetic and photonic probes image their magnetic and dielectric structure while sharp tips probe mechanical properties like surface topography, friction or stiffness. Most of these observables, however, are accessible only under limited circumstances. For instance, electronic properties are measurable only on conducting samples while atomic-resolution force microscopy requires careful preparation of samples in ultrahigh vacuum or liquid environments. Here we demonstrate a scanning probe imaging method that extends the range of accessible quantities to label-free imaging of chemical species operating on arbitrary samples - including insulating materials - under ambient conditions. Moreover, it provides three-dimensional depth information, thus revealing subsurface features. We achieve these results by recording nuclear magnetic resonance signals from a sample surface with a recently introduced scanning probe, a single nitrogen-vacancy center in diamond. We demonstrate NMR imaging with 10 nm resolution and achieve chemically specific contrast by separating fluorine from hydrogen rich regions. Our result opens the door to scanning probe imaging of the chemical composition and atomic structure of arbitrary samples. A method with these abilities will find widespread application in material science even on biological specimens down to the level of single macromolecules.
In this work we present the results of an experiment to locally resolve the spin Seebeck effect in a high-quality Pt/YIG sample. We achieve this by employing a locally heated scanning thermal probe to generate a highly local non-equilibrium spin current. To support our experimental results, we also present a model based on the non-equilibrium thermodynamic approach which is in a good agreement with experimental findings. To further corroborate our results, we index the locally resolved spin Seebeck effect with that of the local magnetisation texture by MFM and correlate corresponding regions. We hypothesise that this technique allows imaging of magnetisation textures within the magnon diffusion length and hence characterisation of spin caloritronic materials at the nanoscale.
Two-dimensional heterostructures with layers of slightly different lattice vectors exhibit a new periodic structure known as moire lattices. Moire lattice formation provides a powerful new way to engineer the electronic structure of two-dimensional materials for realizing novel correlated and topological phenomena. In addition, superstructures of moire lattices can emerge from multiple misaligned lattice vectors or inhomogeneous strain distribution, which offers an extra degree of freedom in the electronic band structure design. High-resolution imaging of the moire lattices and superstructures is critical for quantitative understanding of emerging moire physics. Here we report the nanoscale imaging of moire lattices and superstructures in various graphene-based samples under ambient conditions using an ultra-high-resolution implementation of scanning microwave impedance microscopy. We show that, quite remarkably, although the scanning probe tip has a gross radius of ~100 nm, an ultra-high spatial resolution in local conductivity profiles better than 5 nm can be achieved. This resolution enhancement not only enables to directly visualize the moire lattices in magic-angle twisted double bilayer graphene and composite super-moire lattices, but also allows design path toward artificial synthesis of novel moire superstructures such as the Kagome moire from the interplay and the supermodulation between twisted graphene and hexagonal boron nitride layers.
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