University of Münster Visualizes Buried Magnetic States with Microscopy

Researchers at the University of Münster, led by Prof Anika Schlenhoff and Dr Maciej Bazarnik, have modified scanning tunnelling microscopy to visualise magnetic properties beneath material surfaces, previously requiring destructive analysis. By employing a resonant measurement variant, the team imaged both structural and magnetic properties of an ultra-thin iron film covered by graphene, detecting local magnetic properties and variations in atomic stacking sequences. This advancement allows for the simultaneous investigation of layered systems’ top and buried interfacial layers with atomic-scale resolution, offering enhanced materials characterisation capabilities.

Visualising Buried Magnetic States

Researchers at the University of Münster have developed a resonant variant of scanning tunnelling microscopy capable of imaging properties beyond the uppermost atomic layer of a material. This technique investigates states located in front of the surface, which facilitates the investigation of electronic charge transfer at buried interfaces, and allows for the detection of local magnetic properties of underlying layers. The team successfully demonstrated the ability to detect the local magnetic properties of an ultra-thin iron film covered by a graphene layer, a feat previously requiring destructive material analysis.

This advancement in materials characterisation technology allows for the simultaneous investigation of both the top layer and a buried interfacial layer within a layered system, in terms of structural, electronic, and magnetic properties. Both layers can be analysed with uniquely high spatial resolution, extending down to the atomic scale, providing detailed insights into material composition and behaviour. The underlying physical principle relies on the penetration of surface-adjacent states, which become magnetised through interaction with the resonant scanning tunnelling microscopy.

Furthermore, the technique can resolve variations in the local position of layers for this material. For this process, variations in carbon atoms within the graphene layer, due to differing stacking sequences, could be resolved. This represents an improvement over conventional scanning tunnelling microscopy, which had previously been unable to resolve these differences in vertical stacking for this material system. The technique is sensitive to these variations, thus allowing these differences to be visualised.

Resonant Scanning Tunneling Microscopy Explained

The underlying physical principle involves the penetration of these surface-adjacent electronic states beneath the graphene layer, reaching the magnetic iron layer and becoming magnetised through interaction with it. This allows the microscope to effectively ‘see’ the magnetic properties of the buried iron film, revealing a contrast between areas with differing stacking sequences alongside a map of local spin polarisation stemming from spin density at the buried interface.

This advancement offers significant potential for materials characterisation, as the same scanning tunnelling microscope can now be used to investigate both the top layer of a layered system and a buried interfacial layer, in terms of their structural, electronic, and magnetic properties. Both layers can be analysed with uniquely high spatial resolution, extending down to the atomic scale.

Furthermore, the team demonstrated the ability to obtain information about the local position of the layers relative to each other, resolving variations in the position of carbon atoms within the graphene layer relative to the underlying iron atoms due to differing stacking sequences. Conventional scanning tunnelling microscopy had previously been unable to resolve these differences in vertical stacking for this material system, as the states near the surface, utilised in resonant scanning tunnelling microscopy, are sensitive to the stacking sequence.

Implications for Materials Characterisation

This resonant variant of scanning tunnelling microscopy extends the capabilities of materials characterisation technology by enabling the investigation of both structural and magnetic properties simultaneously. The technique allows for the analysis of both the top layer of a layered system and a buried interfacial layer, achieving uniquely high spatial resolution down to the atomic scale.

Furthermore, the method provides information regarding the local positioning of layers relative to each other, specifically resolving variations in the position of carbon atoms within a graphene layer relative to underlying iron atoms. These variations arise from differing stacking sequences, a feature previously unresolvable with conventional scanning tunnelling microscopy. The sensitivity of the employed states to stacking sequence facilitates the visualisation of these differences.