The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform

Gareth A Morris - One of the best experts on this subject based on the ideXlab platform.

  • improving the accuracy of pulsed Field Gradient nmr diffusion experiments correction for Gradient non uniformity
    Journal of Magnetic Resonance, 2009
    Co-Authors: Mark A Connell, Paul Bowyer, Adam P Bone, Adrian L V Davis, Alistair G Swanson, Mathias Nilsson, Gareth A Morris
    Abstract:

    Pulsed Field Gradient NMR is a well-established technique for the determination of self-diffusion coefficients. However, a significant source of systematic error exists in the spatial variation of the applied pulsed Field Gradient. Non-uniform pulsed Field Gradients cause the decay of peak amplitudes to deviate from the expected exponential dependence on Gradient squared. This has two undesirable effects: the apparent diffusion coefficient will deviate from the true value to an extent determined by the choice of experimental parameters, and the error estimated by the nonlinear least squares fitting will contain a significant systematic contribution. In particular, the apparent diffusion coefficient determined by exponential fitting of the diffusional attenuation of NMR signals will depend both on the exact pulse widths used and on the range of Gradient amplitudes chosen. These problems can be partially compensated for if experimental attenuation data are fitted to a function corrected for the measured spatial dependence of the Gradient and signal strength. This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements. The dominant longitudinal variation of the pulsed Field Gradient amplitude and the signal strength are mapped by measuring pulsed Field Gradient echoes in the presence of a weak read Gradient. These data are then used to construct a predicted signal decay function for the whole sample, which is parameterised as the exponential of a power series. Results are presented which compare diffusion coefficients obtained using the new calibration method with previous literature values.

M. Igarashi - One of the best experts on this subject based on the ideXlab platform.

  • Write-Field Gradient effect on transition width in perpendicular recording media
    2005 IEEE International Magnetics Conference (INTERMAG), 2005
    Co-Authors: M. Mochizuki, M. Hara, A. Nakamura, M. Igarashi
    Abstract:

    Perpendicular magnetic recording (PMR) system using a single-pole writer and a double-layered perpendicular recording medium with a soft underlayer (SUL) is a promising candidate for high recording densities of over 100 Gb/in/sup 2/. The relationships between medium characteristics and recording performance have been studied. In this paper, we have clarified the dependency of the write-Field Gradient on the transition width using by a micromagnetic modeling. Also, the dependence of medium parameters is also discussed in the paper.

  • Write-Field Gradient effect on transition width in perpendicular recording media
    IEEE Transactions on Magnetics, 2005
    Co-Authors: M. Mochizuki, M. Hara, A. Nakamura, M. Igarashi
    Abstract:

    The effect of the write-Field Gradient on recording resolution and transition width was investigated using a micromagnetic simulation. The ultrahigh write-Field Gradient, which is greater than 1000 Oe/nm, produced a very small transition width. The effect of write-Field Gradient on recording resolution and transition width decreased with decreasing the distribution of the anisotropy Field.

Mark A Connell - One of the best experts on this subject based on the ideXlab platform.

  • improving the accuracy of pulsed Field Gradient nmr diffusion experiments correction for Gradient non uniformity
    Journal of Magnetic Resonance, 2009
    Co-Authors: Mark A Connell, Paul Bowyer, Adam P Bone, Adrian L V Davis, Alistair G Swanson, Mathias Nilsson, Gareth A Morris
    Abstract:

    Pulsed Field Gradient NMR is a well-established technique for the determination of self-diffusion coefficients. However, a significant source of systematic error exists in the spatial variation of the applied pulsed Field Gradient. Non-uniform pulsed Field Gradients cause the decay of peak amplitudes to deviate from the expected exponential dependence on Gradient squared. This has two undesirable effects: the apparent diffusion coefficient will deviate from the true value to an extent determined by the choice of experimental parameters, and the error estimated by the nonlinear least squares fitting will contain a significant systematic contribution. In particular, the apparent diffusion coefficient determined by exponential fitting of the diffusional attenuation of NMR signals will depend both on the exact pulse widths used and on the range of Gradient amplitudes chosen. These problems can be partially compensated for if experimental attenuation data are fitted to a function corrected for the measured spatial dependence of the Gradient and signal strength. This study describes a general alternative to existing methods for the calibration of NMR diffusion measurements. The dominant longitudinal variation of the pulsed Field Gradient amplitude and the signal strength are mapped by measuring pulsed Field Gradient echoes in the presence of a weak read Gradient. These data are then used to construct a predicted signal decay function for the whole sample, which is parameterised as the exponential of a power series. Results are presented which compare diffusion coefficients obtained using the new calibration method with previous literature values.

M. Mochizuki - One of the best experts on this subject based on the ideXlab platform.

  • Write-Field Gradient effect on transition width in perpendicular recording media
    2005 IEEE International Magnetics Conference (INTERMAG), 2005
    Co-Authors: M. Mochizuki, M. Hara, A. Nakamura, M. Igarashi
    Abstract:

    Perpendicular magnetic recording (PMR) system using a single-pole writer and a double-layered perpendicular recording medium with a soft underlayer (SUL) is a promising candidate for high recording densities of over 100 Gb/in/sup 2/. The relationships between medium characteristics and recording performance have been studied. In this paper, we have clarified the dependency of the write-Field Gradient on the transition width using by a micromagnetic modeling. Also, the dependence of medium parameters is also discussed in the paper.

  • Write-Field Gradient effect on transition width in perpendicular recording media
    IEEE Transactions on Magnetics, 2005
    Co-Authors: M. Mochizuki, M. Hara, A. Nakamura, M. Igarashi
    Abstract:

    The effect of the write-Field Gradient on recording resolution and transition width was investigated using a micromagnetic simulation. The ultrahigh write-Field Gradient, which is greater than 1000 Oe/nm, produced a very small transition width. The effect of write-Field Gradient on recording resolution and transition width decreased with decreasing the distribution of the anisotropy Field.

Y. Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • High-Field Gradient single-pole head with an improved pole structure
    IEEE Transactions on Magnetics, 2002
    Co-Authors: H. Muraoka, Y. Nakamura
    Abstract:

    The relationship between the head Field and the pole structure in a single-pole head is investigated by finite-element method calculation. The calculation reveals that the regular single-pole head does show a relatively large Field Gradient with a maximum of 150 Oe/mn, which is crucial for high-resolution recording, but only for relatively large Field strength. By placing an additive pole in the vicinity of the main pole, the head-Field Gradient is improved. The new pole structure increases the Gradient up to 250 Oe/nm. The large Field Gradient is obtained in a wider range of Field strength than the regular single-pole head. The calculation also shows a simulated recorded transition when the large head Field Gradient becomes narrow.

  • High Field Gradient single pole head with a novel pole structure
    2002 IEEE International Magnetics Conference (INTERMAG), 2002
    Co-Authors: H. Muraoka, Y. Nakamura
    Abstract:

    Summary form only given. In perpendicular recording, writing head Field Gradient affects not only high density characteristics but also media noise. Improvement of the single pole head (SPT head) to realize a high Field Gradient is therefore critical. Based on the cusp Field SPT head, the structure optimization by locating the upper return path in the vicinity of the main pole was investigated to increase the Gradient with a 2D FEM calculation. Resultant recorded transition widths were examined as well.

  • Effect of head Field Gradient on transition jitter in perpendicular magnetic recording
    IEEE Transactions on Magnetics, 2001
    Co-Authors: K. Miura, H. Muraoka, Y. Nakamura
    Abstract:

    Noise of perpendicular double-layered media was investigated in connection with write head Field of single pole heads. Time-domain noise measurement revealed that the noise was spatially concentrated around transitions, caused by transition jitter. The influence of writing head Field was discussed based on jitter measurement using various heads; a ring head and single pole heads. The amount of transition jitter was inversely proportional to estimated writing head Field Gradient. The writing head Field improvement, thus, contributed to reduce the medium noise.