Munir Dede

50 nm Hall Sensors for Room Temperature Scanning Hall Probe Microscopy

Bismuth nano-Hall sensors with dimensions ~50 nm × 50 nm were fabricated using a combination of optical lithography and focused ion beam milling. The Hall coefficient, series resistance and optimum magnetic field sensitivity of the sensors were 4×10-4 Ω/G, 9.1 kΩ and 0.8 G/√Hz, respectively. A 50 nm nano-Bi Hall sensor was installed into a room temperature scanning Hall probe microscope and successfully used for directly imaging ferromagnetic domains of low coercivity garnet thin films.

Room-temperature scanning Hall probe microscope (RT-SHPM) imaging of garnet films using new high-performance InSb sensors

High-performance InSb micro-Hall sensors were fabricated by optical lithography and incorporated in a room-temperature scanning Hall probe microscope for imaging of localized magnetic fluctuations in close proximity to the surfaces of crystalline uniaxial garnet films. The room-temperature noise figure of the InSb sensors was 6-10 mG//spl radic/Hz, which is an order of magnitude. better than GaAs-AlGaAs two-dimensional electron gas sensors used to date.

High sensitivity and multifunctional micro-Hall sensors fabricated using InAlSb/InAsSb/InAlSb heterostructures

M. Bando, T. Ohashi, M. Dede, R. Akram, A. Oral, S. Park, M. Abe, H. Handa, I. Shibasaki and A. Sandhu

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

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.

Variable Temperature-Scanning Hall Probe Microscopy With GaN/AlGaN Two-Dimensional Electron Gas (2DEG) Micro Hall Sensors in 4.2–425 K Range Using Novel Quartz Tuning Fork AFM Feedback

In this paper, we present the fabrication and variable temperature (VT) operation of Hall sensors, based on GaN/AlGaN heterostructure with a two-dimensional electron gas (2DEG) as an active layer, integrated with quartz tuning fork (QTF) in atomic force-guided (AFM) scanning Hall probe microscopy (SHPM). Physical strength and a wide bandgap of GaN/AlGaN heterostructure makes it a better choice to be used for SHPM at elevated temperatures, compared to other compound semiconductors (AlGaAs/GaAs and InSb), which are unstable due to their narrower bandgap and physical degradation at high temperatures. GaN/AlGaN micro Hall probes were produced using optical lithography and reactive ion etching. The active area, Hall coefficient, carrier concentration, and series resistance of the Hall sensors were ~1times1 mum, 10 mOmega/G at 4.2 K, 6.3 times 1012 cm-2 and 12 kOmega at room temperature and 7 mOmega/G, 8.9 times 1012 cm-2 and 24 kOmega at 400 K, respectively. A novel method of AFM feedback using QTF has been adopted. This method provides an advantage over scanning tunneling-guided feedback, which limits the operation of SHPM the conductive samples and failure of feedback due to high leakage currents at high temperatures. Simultaneous scans of magnetic and topographic data at various pressures (from atmospheric pressure to high vacuum) from 4. to 425 K will be presented for different samples to illustrate the capability of GaN/AlGaN Hall sensors in VT-SHPM.

Imaging capability of pseudomorphic high electron mobility transistors, AlGaN/GaN, and Si micro-Hall probes for scanning Hall probe microscopy between 25 and 125 °C

The authors present a comparative study on imaging capabilities of three different micro-Hall probe sensors fabricated from narrow and wide band gap semiconductors for scanning hall probe microscopy at variable temperatures. A novel method of quartz tuning fork atomic force microscopy feedback has been used which provides extremely simple operation in atmospheric pressures, high-vacuum, and variable-temperature environments and enables very high magnetic and reasonable topographic resolution to be achieved simultaneously. Micro-Hall probes were produced using optical lithography and reactive ion etching process. The active area of all different types of Hall probes were 1×1μm2. Electrical and magnetic characteristics show Hall coefficient, carrier concentration, and series resistance of the hall sensors to be 10mΩ∕G, 6.3×1012cm−2, and 12kΩ at 25°C and 7mΩ∕G, 8.9×1012cm−2 and 24kΩ at 125°C for AlGaN∕GaN two-dimensional electron gas (2DEG), 0.281mΩ∕G, 2.2×1014cm−2, and 139kΩ at 25°C and 0.418mΩ∕G, 1.5×1014c...

Real-Time Imaging of Vortex–Antivortex Annihilation in Bi2Sr2CaCu2O8+δ Single Crystals by Low Temperature Scanning Hall Probe Microscopy

Vortices in superconductors play an important role in operating limits and applications of the superconductors. Scanning Hall probe microscopes have proven themselves to be quantitative and non-invasive tools for investigating magnetic samples down to 50 nm scale. Penetration of vortices in high quality single crystal Bi2Sr2CaCu2O8+δ superconductor has been studied in real-time with single vortex resolution at 77 K using a low temperature scanning Hall probe microscope (LT-SHPM). Vortices have been observed to be annihilated by the antivortices in small M–H loops.

Bean–Livingston surface barriers for flux penetration in Bi2Sr2CaCu2O8+δ single crystals near the transition temperature

We report on transient effects in the microwave second-order response of different type of superconductors in the mixed state. The samples have contemporarily been exposed to a dc magnetic field, varying with a constant rate of 60 Oe/s, and a pulsed microwave magnetic field. The time evolution of the signal radiated at the second-harmonic frequency of the driving field has been measured for about 500 s from the instant in which the dc-field sweep has been stopped, with sampling time of ∼ 0.3 s. We show that the second-harmonic signal exhibits two relaxation regimes; an initial exponential decay, which endures roughly 10 s, and a logarithmic decay in the time scale of minutes. Evidence is given that the decay in the time scale of minutes is ruled by magnetic relaxation over the surface barrier. PACS. 74.25.Ha Magnetic properties – 74.25.Nf Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) – 74.60.Ge Flux pinning, flux creep, and flux-line lattice dynamics

Variable Temperature Scanning Hall Probe Microscopy (SHPM) Using Quartz Crystal AFM Feedback

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The resultant SHPM can operate in variable temperature environment, 77-300 K.

Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The resultant SHPM can operate in variable temperature environment, 77-300 K.