Scanning SQUID-on-tip microscope in a top-loading cryogen-free dilution refrigerator

Abstract

The scanning superconducting quantum interference device (SQUID) fabricated on the tip of a sharp quartz pipette (SQUID-on-tip) has emerged as a versatile tool for nanoscale imaging of magnetic, thermal, and transport properties of microscopic devices of quantum materials. We present the design and performance of a scanning SQUID-on-tip microscope in a top-loading probe of a cryogen-free dilution refrigerator. The microscope is enclosed in a custom-made vacuum-tight cell mounted at the bottom of the probe and is suspended by springs to suppress vibrations caused by the pulse tube cryocooler. Two capillaries allow in-situ control of helium exchange gas pressure in the cell that is required for thermal imaging. A nanoscale heater is used to create local temperature gradients in the sample, which enables quantitative characterization of the relative vibrations between the tip and the sample. The spectrum of the vibrations shows distinct resonant peaks with maximal power density of about 27 nm/Hz${}^{1/2}$ in the in-plane direction. The performance of the SQUID-on-tip microscope is demonstrated by magnetic imaging of the MnBi${}_2$Te${}_4$ magnetic topological insulator, magnetization and current distribution imaging in a SrRuO${}_3$ ferromagnetic oxide thin film, and by thermal imaging of dissipation in graphene.

Submitted to Review of Scientific Instruments

References in corpus (10)

• Interface-driven topological Hall effect in SrRuO${}_3$-SrIrO${}_3$ bilayer
• Imaging of super-fast dynamics and flow instabilities of superconducting vortices
• Robust A-type order and spin-flop transition on the surface of the antiferromagnetic topological insulator MnBi${}_2$Te${}_4$
• Imaging resonant dissipation from individual atomic defects in graphene
• SQUID-on-tip with single-electron spin sensitivity for high-field and ultra-low temperature nanomagnetic imaging
• Coexistence of surface and bulk ferromagnetism mimics skyrmion Hall effect in a topological insulator
• Scanning nitrogen-vacancy magnetometry down to 350mK
• Interior and edge magnetization in thin exfoliated CrGeTe3 films
• Development of a near-5-Kelvin, cryogen-free, pulse-tube refrigerator-based scanning probe microscope
• Determining the vibrations between sensor and sample in SQUID microscopy