Browsing by Author "Masuda, H."

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    Bismuth nano-Hall probes fabricated by focused ion beam milling for direct magnetic imaging by room temperature scanning Hall probe microscopy
    (The Institution of Engineering and Technology (IET), 2001) Sandhu, A.; Masuda, H.; Kurosawa, K.; Oral, A.; Bending, S. J.
    Bismuth nano-Hall probes fabricated by using focused ion beam (FIB) milling were studied. The nano-Hall probes were used for direct magnetic imaging of domain structures in low coercivity garnets and demagnetized strontium ferrite permanent magnets. The analysis was performed using room temperature scanning Hall probe microscopy and it was found that the Bi nano-probes could overcome limitations due to surface depletion and large series resistances.
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    Direct magnetic imaging of ferromagnetic domain structures by room temperature scanning hall probe microscopy using a bismuth micro-Hall probe
    (Japan Society of Applied Physics, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
    A bismuth micro-Hall probe sensor with an integrated scanning tunnelling microscope tip was incorporated into a room temperature scanning Hall probe microscope system and successfully used for the direct magnetic imaging of microscopic domains of low coercivity perpendicular garnet thin films and demagnetized strontium ferrite permanent magnets. At a driving current of 800 μA, the Hall coefficient, magnetic field sensitivity and spatial resolution of the Bi probe were 3.3 × 10-4 Ω/G, 0.38 G/√Hz and ∼ 2.8 μm, respectively. The room temperature magnetic field sensitivity of the Bi probe was comparable to that of a semiconducting 1.2μm GaAs/AlGaAs heterostructure micro-Hall probe, which exhibited a value of 0.41 G/√Hz at a maximum driving current of 2μA.
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    Room temperature magnetic imaging of magnetic storage media and garnet epilayers in the presence of external magnetic fields using a sub-micron GaAs SHPM
    (Elsevier, 2001-07) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
    A multipurpose room temperature scanning Hall probe microscope (RT-SHPM) system incorporating an ultra-high sensitive sub-micron GaAs Hall probe (active area of similar to0.8 x 0.8 mum(2) room temperature Hall coefficient of 0.3 Ohm /G) exhibiting extremely high magnetic field sensitivity (0.04G/root Hz) was used for the direct, non-invasive and quantitative imaging of magnetic field fluctuations in very close proximity to the surfaces of thin film magnetic storage media, Bi substituted iron garnet epilayers and demagnetized Sr-ferrite permanent magnets placed in external magnetic fields. A scanning tunnelling microscope tip integrated adjacent to the Hall probe was used for precise vertical positioning of the probe. RT-SHPM images of 1.4 MB written floppy disks clearly showed well-defined magnetic transitions to coalesce into small island-like structures under external perpendicular fields greater than 1300 Oe. The RT-SHPM is demonstrated to be a versatile means of quantitatively monitoring micron-sized magnetic domain structures in the presence of external magnetic fields at: room temperature. (C) 2001 Elsevier Science B.V. All rights reserved.
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    Room temperature Scanning Hall Probe Microscopy in external Fields
    (Magnetics Society of Japan, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
    A new versatile room temperature scanning Hall probe microscope system (RT-SHPM) was developed and used for the magnetic imaging of longitudinal magnetic recording media, low coercivity perpendicularly anisotropic iron garnet epitaxial layers, and demagnetized strontium ferrite permanent magnets placed in externally applied magnetic fields. The RT-SHPM incorporates an ultra-high sensitive sub-micron GaAs Hall probe (active area of ∼ 0.8x0.8 μm2; room temperature Hall coefficient of 0.3Ω/G; field sensitivity of 0.04 G/√Hz) with an integrated scanning tunnelling microscope tip for vertically positioning the probe in very close proximity to sample surfaces. The Hall probe is not magnetized by magnetic fields hence enabling the real time (∼1 frame/sec) measurments in external magnetic fields. Results described include the observation of otherwise sharp magnetic transitions in written floppy disks to coalesce into small islands under external fields greater than 1300 Oe and the transformation of magnetic bubble lattices into striped-maze patterns in Bi-substituted iron garnet epilayers in cycled external fields.
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    Room temperature scanning Hall probe microscopy of localized magnetic field fluctuations on the surfaces of magnetic recording media, permanent magnets and crystalline garnet films in external bias fields
    (Elsevier B.V., 2002-04) Sandhu, A.; Iida, N.; Masuda, H.; Oral, A.; Bending, S. J.
    A sub-micron room temperature scanning Hall probe microscope (RT-SHPM) was used for real-time imaging of surface magnetic domains of floppy disks, Sr ferrite magnets and Bi-substituted iron garnets placed in large external bias fields. Domain wall nucleation was observed in the garnets where bubble lattices expanded, collapsed and transformed into stripe domains in cyclic bias fields. Evolution of RT-SHPM images was compared with conventional vibrating sample magnetometer measurements.
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    Room temperature scanning Hall probe microscopy using GaAs/AlGaAs and Bi micro-hall probes
    (Elsevier Science B.V., 2002) Sandhu, A.; Masuda, H.; Oral, A.; Yamada, A.; Konagai, M.
    A room temperature scanning Hall probe microscope system utilizing GaAs/AlGaAs and bismuth micro-Hall probes was used for magnetic imaging of ferromagnetic domain structures on the surfaces of crystalline thin film garnets and permanent magnets. The Bi micro-Hall probes had dimensions ranging between 0.25 and 2.8μm2 and were fabricated using a combination of optical lithography and focused ion beam milling. The use of bismuth was found to overcome surface depletion effects associated with semiconducting micro-Hall probes. Our experiments demonstrated that Bi is a practical choice of material for fabricating sub-micron sized Hall sensors.
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    Room Temperature Scanning Micro-Hall Probe Microscope Imagingof Ferromagnetic Microstructures in the Presence of 2.5 Tesla Pulsed Magnetic FieldsGenerated by an Integrated Mini Coil
    (Institute of Physics Publishing, 2002) Sandhu, A.; Masuda, H.; Oral, A.
    A unique magnetic imaging system comprising of a room temperature scanning Hall probe microscope with an integratedmini-coil capable of generating pulsed magnetic fields up to 2.5 Tesla (width of 3 ms) was developed for the direct andnon-invasive magnetic imaging of ferromagnetic micro-domains in the presence of extremely large external pulsed mag-netic fields without adverse vibrational disturbance of the sample during measurements. The system was successfully usedfor magnetic imaging of the erasure process of bit patterns on the surface of 1.4 MB written floppy disks and the dynamicsof micro-domain structures of demagnetized strontium ferrite permanent magnets under large external pulsed magnetic fields.
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    Room Temperature Scanning Micro-Hall Probe Microscopy Under Extremely Large Pulsed Magnetic Fields
    (IEEE, 2003) Sandhu, A.; Masuda, H.; Oral, A.
    Abstract The versatility of a room-temperature scanning Hall probe microscope system with an integrated minicoil capable of generating pulsed magnetic fields up to 2.9 T was demonstrated by imaging magnetic structures on the surface of 1.4-MB floppy disks and demagnetized strontium ferrite permanent magnets. Vibration isolation between the sample and minicoil was achieved by using a combination of quartz glass plates and silicone gel layers and enabled extremely fast measurements under fields as high as 2.9 T, without detrimental effects on a GaAs-AlGaAs micro-Hall probe sensor located at a height of 0.5 mum above-the sample surface.
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    Room temperature sub-micron magnetic imaging by scanning hall probe microscopy
    (Japan Society of Applied Physics, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
    An ultra-high sensitive room temperature scanning Hall probe microscope (RT-SHPM) system incorporating a GaAs/A1GaAs micro-Hall probe was used for the direct magnetic imaging of localized magnetic field fluctuations in very close proximity to the surface of ferromagnetic materials. The active area, Hall coefficient and field sensitivity of the Hall probe were 0.8 μm×0.8 μm, 0.3 Ω/G and 0.04 G/√Hz, respectively. The use of a semiconducting Hall probe sensor enabled measurements in the presence of externally applied magnetic fields. Samples studied included magnetic recording media, demagnetized strontium ferrite permanent magnets, and low coercivity perpendicular garnet thin films. The RT-SHPM offers a simple means for quantitatively monitoring sub-micron magnetic domain structures at room temperature.
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    Room-temperature scanning Hall probe microscope (RT-SHPM) imaging of garnet films using new high-performance InSb sensors
    (IEEE, 2002) Oral, Ahmet; Kaval, Murat; Dede, Münir; Masuda, H.; Okamoto, A.; Shibasaki, I.; Sandhu, A.
    The room-temperature scanning Hall probe microscopy (RT-SHPM) imaging of garnet films using high-performance InSb sensors was discussed. The high-performance InSb micro-Hall sensors were fabricated by optical lithography. It was found that the room-temperature noise figure of the InSb sensors was 6-10 mG/√Hz, which was an order of magnitude better than GaAs-AlGaAs two-dimensional electron gas sensors.