# Cryogen-free variable temperature scanning SQUID microscope

## TL;DR

This paper presents a cryogen-free variable temperature scanning SQUID microscope mounted on a cryocooler, achieving low vibrations and enabling magnetic imaging of high-temperature superconductors from 2.8 K to 110 K.

## Contribution

It introduces a cryogen-free setup with passive vibration isolation and a variable-temperature stage for high-resolution magnetic imaging.

## Key findings

- Achieved in-plane vibrations of 20 nm and out-of-plane of 15 nm.
- Enabled imaging of vortex pinning in YBCO above 90 K.
- Operated effectively from 2.8 K to 110 K.

## Abstract

Scanning Superconducting QUantum Interference Device (SQUID) microscopy is a powerful tool for imaging local magnetic properties of materials and devices, but it requires a low-vibration cryogenic environment, traditionally achieved by thermal contact with a bath of liquid helium or the mixing chamber of a "wet" dilution refrigerator. We mount a SQUID microscope on the 3 K plate of a Bluefors cryocooler and characterize its vibration spectrum by measuring SQUID noise in a region of sharp flux gradient. By implementing passive vibration isolation, we reduce relative sensor-sample vibrations to 20 nm in-plane and 15 nm out-of-plane. A variable-temperature sample stage that is thermally isolated from the SQUID sensor enables measurement at sample temperatures from 2.8 K to 110 K. We demonstrate these advances by imaging inhomogeneous diamagnetic susceptibility and vortex pinning in optimally-doped YBCO above 90 K.