Magnetic Force Microscopy Imaging of Magnetic Vortices in Superconductors

By AZoNano Staff Writers

Table of Content

Introduction
Experimental Framework
Conclusion
About NanoScan AG

Introduction

The combination of NanoScan PPMS®-AFM and Quantum Design PPMS® enables users to image individual magnetic flux vortices in a superconductor at varying external magnetic field and low temperatures. This article describes MFM (magnetic force microscopy) measurements that display magnetic vortices in a single crystal niobium, and a newly discovered superconductor, iron pnictide.

Experimental Framework

In this study, the specimens were mounted in the PPMS®-AFM sans any additional preparation and cooled to below their temperature in a tiny magnetic field. Then, all MFM images were obtained at a stable average height. It was observed that the first three MFM images displayed vortices in the surface of iron pnictide.

Figure 1. Sample of iron pnictide

Subsequently, the first two images were obtained at the same position. It was observed that when external magnetic field increased, the density of the magnetic vortices also increased correspondingly.

The yellow arrow in the third MFM image signifies a terrace step which is a topographical element. The fourth image displays individual vortices in the surface of the crystal niobium sample. This image was acquired subsequent to cooling in a field of 30 Oe to 4.4K.

The final picture (Figures a - b) displays a range of unprocessed images (circled in red) that were acquired in the same area. The vortices displayed in the upper two images have a polarisation which is antiparallel to the tip magnetisation (bright spots). Here, a similar effect as on the iron pnictide was observed.

The vortices displayed in the lower two images have a polarisation which is parallel to the tip magnetisation (dark spots) with the same external magnetic field. It was possible to distinguish that one vortex has vanished between the acquirement of the two images.

Conclusion

From the above experiment, it is evident that the NanoScan PPMS®-AFM coupled with the Quantum Design PPMS® helps in imaging individual superconducting vortices even at unstable external magnetic field and low temperatures.

About NanoScan AG

With excellent know-how in the fast growing field of nanoscience, the main focus of NanoScan Ltd is on research and development of high-resolution and versatile magnetic and non-contact scanning force microscopes. These instruments are especially designed to fulfill the present and future analytical needs on nanometer-sized surface structures.

This information has been sourced, reviewed and adapted from materials provided by NanoScan AG.

For more information on this source, please visit NanoScan AG.

Date Added: Dec 17, 2013 | Updated: Jan 3, 2014
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