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The Scanning TMR Microscope for Biosensor Applications.

Vyas KN, Love DM, Ionescu A, Llandro J, Kollu P, Mitrelias T, Holmes S, Barnes CH - Biosensors (Basel) (2015)

Bottom Line: We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D.By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe.By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, CB3-0HE Cambridge, UK. kunalnvyas@gmail.com.

ABSTRACT
We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D. By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe. By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance. The modular design, incorporating a TMR sensor with an optical microscope, renders this set-up a versatile platform for studying and imaging immobilised magnetic carriers and barcodes currently employed in biosensor platforms, magnetotactic bacteria and other complex magnetic domain structures of micron-sized entities. The quantitative nature of the instrument and its ability to produce vector maps of magnetic stray fields has the potential to provide significant advantages over other commonly used scanning magnetometry techniques.

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(a) Two three-bit tags are scanned in forward (above) and reverse (below) direction, showing a high level of reproducibility. A 10 µm/s scan speed was used with a measurement time-constant of 500 ms. The vertical distance between the sample and sensor is ≈5 µm; (b) A single magnetic element scanned along its long axis at 10 µm/s with a 100 ms time constant. The scan shows that the signal level increases as you travel form the centre of the element to the edge, after which the signal changes sign before dying away. The sensitive axis the TMR sensor for (a) and (b) points along the length of the magnetic elements.
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biosensors-05-00172-f005: (a) Two three-bit tags are scanned in forward (above) and reverse (below) direction, showing a high level of reproducibility. A 10 µm/s scan speed was used with a measurement time-constant of 500 ms. The vertical distance between the sample and sensor is ≈5 µm; (b) A single magnetic element scanned along its long axis at 10 µm/s with a 100 ms time constant. The scan shows that the signal level increases as you travel form the centre of the element to the edge, after which the signal changes sign before dying away. The sensitive axis the TMR sensor for (a) and (b) points along the length of the magnetic elements.

Mentions: TMR line scans were taken of Co magnetic elements of varying aspect ratios (1:8, 1:5, 1:2.5), ∼20 nm thick, 20 µm long and approximately 40 µm apart. The samples were grown on a glass substrate, so that they could be simultaneously viewed using the optical microscope. Scans were taken, scanning across several magnetic elements, with the long, magnetically easy, axis of the elements perpendicular to the scan path and parallel to the sensitive direction of the TMR sensor. Figure 5a shows the field as measured by a TMR sensor as it was scanned at 10 µm/s across two three-bit tags in the forward and reverse directions. A frequency of 833 Hz was used with a time constant of 500 ms.


The Scanning TMR Microscope for Biosensor Applications.

Vyas KN, Love DM, Ionescu A, Llandro J, Kollu P, Mitrelias T, Holmes S, Barnes CH - Biosensors (Basel) (2015)

(a) Two three-bit tags are scanned in forward (above) and reverse (below) direction, showing a high level of reproducibility. A 10 µm/s scan speed was used with a measurement time-constant of 500 ms. The vertical distance between the sample and sensor is ≈5 µm; (b) A single magnetic element scanned along its long axis at 10 µm/s with a 100 ms time constant. The scan shows that the signal level increases as you travel form the centre of the element to the edge, after which the signal changes sign before dying away. The sensitive axis the TMR sensor for (a) and (b) points along the length of the magnetic elements.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493544&req=5

biosensors-05-00172-f005: (a) Two three-bit tags are scanned in forward (above) and reverse (below) direction, showing a high level of reproducibility. A 10 µm/s scan speed was used with a measurement time-constant of 500 ms. The vertical distance between the sample and sensor is ≈5 µm; (b) A single magnetic element scanned along its long axis at 10 µm/s with a 100 ms time constant. The scan shows that the signal level increases as you travel form the centre of the element to the edge, after which the signal changes sign before dying away. The sensitive axis the TMR sensor for (a) and (b) points along the length of the magnetic elements.
Mentions: TMR line scans were taken of Co magnetic elements of varying aspect ratios (1:8, 1:5, 1:2.5), ∼20 nm thick, 20 µm long and approximately 40 µm apart. The samples were grown on a glass substrate, so that they could be simultaneously viewed using the optical microscope. Scans were taken, scanning across several magnetic elements, with the long, magnetically easy, axis of the elements perpendicular to the scan path and parallel to the sensitive direction of the TMR sensor. Figure 5a shows the field as measured by a TMR sensor as it was scanned at 10 µm/s across two three-bit tags in the forward and reverse directions. A frequency of 833 Hz was used with a time constant of 500 ms.

Bottom Line: We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D.By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe.By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance.

View Article: PubMed Central - PubMed

Affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, CB3-0HE Cambridge, UK. kunalnvyas@gmail.com.

ABSTRACT
We present a novel tunnel magnetoresistance (TMR) scanning microscope set-up capable of quantitatively imaging the magnetic stray field patterns of micron-sized elements in 3D. By incorporating an Anderson loop measurement circuit for impedance matching, we are able to detect magnetoresistance changes of as little as 0.006%/Oe. By 3D rastering a mounted TMR sensor over our magnetic barcodes, we are able to characterize the complex domain structures by displaying the real component, the amplitude and the phase of the sensor's impedance. The modular design, incorporating a TMR sensor with an optical microscope, renders this set-up a versatile platform for studying and imaging immobilised magnetic carriers and barcodes currently employed in biosensor platforms, magnetotactic bacteria and other complex magnetic domain structures of micron-sized entities. The quantitative nature of the instrument and its ability to produce vector maps of magnetic stray fields has the potential to provide significant advantages over other commonly used scanning magnetometry techniques.

Show MeSH
Related in: MedlinePlus