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

Abstract

We describe the design of a low temperature scanning Hall probe microscope (SHPM) for a dilution refrigerator system. A detachable SHPM head with 25.4 mm OD and 200 mm length is integrated at the end of the mixing chamber base plate of the dilution refrigerator insert (Oxford Instruments, Kelvinox MX−400) by means of a dedicated docking station. It is also possible to use this detachable SHPM head with a variable temperature insert (VTI) for 2 K–300 K operations. A microfabricated 1μm size Hall sensor (GaAs/AlGaAs) with integrated scanning tunneling microscopy tip was used for magnetic imaging. The field sensitivity of the Hall sensor was better than 1 mG/√Hz at 1 kHz bandwidth at 4 K. Both the domain structure and topography of LiHoF4, which is a transverse-field Ising model ferromagnet which orders below TC = 1.53 K, were imaged simultaneously below 40 mK.

A scanning Hall probe microscope for high resolution, large area, variable height magnetic field imaging

“…SHPM is the tool of choice for quantifying the stray fields produced by micro-magnets, which have many applications in bio-medical studies [14][15][16] and MEMS [17]. The present SHPM system demonstrates the usefulness of a combination of concepts, tuning fork feedback based height control, monolithic electronics for regulation and Hall signal read out, scanning with stepper motors, compared to microscopes presented before [8][9][10][11][12][13]18]. Microstructured Hall probes with active area of size 1-5 µm have been fabricated for use in the microscope.…”

“…Though SHPM involves longer image acquisition time than MOI unlike in a scanning probe system, in MOI the whole image is acquired at one time, and involves acquisition times of a few seconds at most) and offers worse spatial resolution compared to MFM, the unique compromise between spatial resolution and field sensitivity makes it a very useful tool for convenient non-destructive quantitative characterization over wide temperature and field ranges. Over the years, efforts have been made to improve the spatial resolution and scan range [8][9][10][11], temperature range [12], and magnetic field resolution [13] of SHPM.…”

The design and the performance of an ultrahigh vacuum 3He fridge-based scanning tunneling microscope with a double deck sample stage for in-situ tip treatment

“…To understand these unique phases of matters, it is necessary to perform the STM and STS measurements at low temperature in the presence of a magnetic field with high energy resolution. Consequently, this has been the motivation for the development of STM systems toward millikelvin temperature with a high magnetic field [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. However, building such a STM system remains challenging because the STM operation in the combination of ultra-low temperature, high magnetic field and ultra-high vacuum (UHV) environments poses stringent constraints for the STM design and optimization.…”

Application of silicon micro hall sensors in variable temperature scanning hall probe microscopy (SHPM) using multiple feedback techniques

“…*Hall sensors are widely used in various applications ranging from high-end industrial and scientific research applications to everyday solutions. Further, micro-Hall sensors have also been used for novel applications including scanning Hall probe microscopy (SHPM) of ferromagnetic domains (Oral et al, 1996;Schweinböck et al, 2000) and as biosensors for the detection of superparamagnetic particles for biorecognition (Mihajlović et al, 2005;Kumagai et al, 2008;Xiao-Fen et al, 2016;Karci et al, 2014). Scanning Hall probe microscopy (SHPM) has been demonstrated as one of the best choices as it provides adequate means to perform sensitive, noninvasive, and quantitative imaging for the investigation of localized surface magnetic field fluctuation at variable temperatures with high spatial resolution and for non-metallic samples.…”