Analysing magnetism using scanning SQUID microscopy

Abstract

Scanning superconducting quantum interference device microscopy (SSM) is a scanning probe technique that images local magnetic flux, which allows for mapping of magnetic fields with high field and spatial accuracy. Many studies involving SSM have been published in the last few decades, using SSM to make qualitative statements about magnetism. However, quantitative analysis using SSM has received less attention. In this work, we discuss several aspects of interpreting SSM images and methods to improve quantitative analysis. First, we analyse the spatial resolution and how it depends on several factors. Second, we discuss the analysis of SSM scans and the information obtained from the SSM data. Using simulations, we show how signals evolve as a function of changing scan height, SQUID loop size, magnetization strength, and orientation. We also investigated 2-dimensional autocorrelation analysis to extract information about the size, shape, and symmetry of magnetic features. Finally, we provide an outlook on possible future applications and improvements.

Structure and magnetic properties of epitaxial CaFe2O4 thin films

“…7) indicate clear magnetic activity. The observed patterns resemble those of a weak ferromagnet 35 , but no clear structure in the signal is visible. This is due to the spatial resolution of the scanning SQUID setup (~5 μm) that causes averaging over multiple domains.…”

“…The experiments were performed with a scanning SQUID microscope 47 with a spatial resolution of approximately 5 μm 35 and field resolution of 50 nT. The samples were cooled and measured in zero background field at 4 K. Various sets of 12 scans of 250 μm × 250 μm size, with 250 μm spacing in between (total covered area about 1.75 mm × 1.75 mm), were collected in different areas to test for homogeneity of the samples.…”

Gate-tuned anomalous Hall effect driven by Rashba splitting in intermixed LaAlO3/GdTiO3/SrTiO3

“…The occurrence of AHE was explained with the polarization of magnetic moments, more specifically by the rotation of moments around the out-of-plane hard axis in a magnetic field perpendicular to the sample surface 28 . In order to investigate this further, we performed measurements with a scanning SQUID microscope 29 on non-gated samples and samples gated at 150 V, 0 V and -150 V. The resulting scans are presented in Supplementary Figure S4 . They did not show any signatures of ferromagnetic domains at 4.2 K, nor did they show ferromagnetic patches such as observed by scanning SQUID in LAO/STO structures 30 – 32 .…”

Granular Hall Sensors for Scanning Probe Microscopy

“…Scanning-probe based imaging of magnetic stray field distributions above a ferromagnetic sample can be accomplished by several complementary techniques, such as magnetic force microscopy (MFM) [1], scanning SQUID microscopy (SSQM) [2,3] and scanning Hall probe microscopy (SHPM) [4,5]. Each of these techniques has particular strengths and weaknesses.…”