An ultra-low temperature scanning Hall probe microscope for magnetic imaging below 40 mK

Area of Science:

• Condensed Matter Physics
• Materials Science
• Cryogenics

Background:

• Scanning Hall probe microscopy (SHPM) is crucial for probing magnetic properties at the nanoscale.
• Dilution refrigerators are essential for achieving ultra-low temperatures required for studying quantum phenomena.

Purpose of the Study:

• To design and implement a detachable SHPM head compatible with a dilution refrigerator system.
• To enable simultaneous imaging of magnetic domain structure and topography at sub-40 mK temperatures.

Main Methods:

• Integration of a detachable SHPM head (25.4 mm OD, 200 mm length) into a dilution refrigerator insert.
• Utilizing a microfabricated 1μm Hall sensor (GaAs/AlGaAs) with an integrated scanning tunneling microscopy tip.
• Achieving field sensitivity better than 1 mG/√Hz at 1 kHz bandwidth at 4 K.

Main Results:

• Successful simultaneous imaging of magnetic domain structure and topography of LiHoF4 below 40 mK.
• Demonstrated the versatility of the SHPM head for both dilution refrigerator and variable temperature insert (2 K-300 K) operations.
• Characterized the magnetic ordering of LiHoF4, a transverse-field Ising model ferromagnet with TC = 1.53 K.

Conclusions:

• The developed SHPM system provides a powerful tool for nanoscale magnetic imaging at ultra-low temperatures.
• The detachable design enhances flexibility for various cryogenic applications.
• This technology facilitates the study of magnetic phase transitions and domain dynamics in novel materials.