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Determination of writing head fields by electron beam tomography
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ELSEVIER
Journal of Magnetism and Magnetic Materials 175 (1997) 111 112
Journalof magnetism and magnetic materials
Determination of writing head fields by electron beam
tomography R.P. Ferrier*, Y. L i u Department of Physics and Astronomy, The University of Glasgow, Glasgow, Scotland G12 8QQ, UK
The quantitative evaluation of recording-head fields is an important aspect of the goal of increased data-storage density for both hard disk and tape recording. Over the last few years, we have developed the method of electron beam tomography, originally introduced by Prof. Kubalek's group at the University of D u i s b u r g [J.B. Elsbrock, W. Schroder, E. Kubalek, IEEE Trans. Magn. 21 (1985) 1337] and applied it to determine the 3D field distributions for advanced thin-film and tape-recording heads. The basis of the method is that we require as input data for the tomographic reconstruction algorithms a number of different 'views' of the magnetic field of the head and this is achieved using the method of differential phase contrast (DPC) imaging in a 200 kV scanning transmission electron microscope [R.P. Ferrier et al., J. Magn. Magn. Mater. 149 (1995) 387]. DPC imaging provides us with signals which are related to orthogonal components of the magnetic induction of the field normal to and integrated along the electron trajectory. The pair of signals are determined along line scans parallel to the ABS as the head is rotated progressively through small angular increments about an axis normal to the optic axis and the ABS. Typically, the angular increment used is A0 = 5° and the total angular range is (180-A0) °. We have available two different reconstruction algorithms; the first is based on back-projection of real-space data and the second on the iterative solution of a set of linear equations. From knowledge of the experimental conditions the field determination may be put on an absolute basis. The wider application of tomographic methods to the study of thin-film heads has been hindered by the experimental difficulty of maintaining the ABS accurately parallel to the optic axis as the head is rotated to collect the full-data set. We have shown that this difficulty can be overcome by deliberately misaligning the head and mounting it so that the ABS is at a small angle to the optic axis; we show that the resulting loss of information relevant to head performance is minimal. Results are presented for IBM OEM heads, where the field-profiles indicate that micromagnetic effects may be present; clearly, this is of great interest because of the inability of current head modeling in this respect. The study of prototype tape heads has also been carried out in collaboration with Philips and Exabyte. These types of head present their own experimental difficulties, which will be discussed briefly, but successful head reconstructions have been achieved and these will be presented.
* Corresponding author. Fax: + 44 41 334 9029; e-mail: [email protected].
0304-8853/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 5 9 1-X
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R.P. Ferrier, E Liu / Journal of Magnetism and Magnetic Materials 175 (1997) l l l
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Without recourse to full tomographic reconstruction, which involves substantial image and data processing and is relatively time consuming, a great deal of valuable information can be obtained from careful study of the DPC line-scan data. The use of these to investigate the onset of head saturation in both tape and thin-film heads will be discussed and also their use in the identification and characterisation of stray-flux production from sites away from the pole-gap region will be described.
ELSEVIER
Journal of Magnetism and Magnetic Materials 175 (1997) 111 112
Journalof magnetism and magnetic materials
Determination of writing head fields by electron beam
tomography R.P. Ferrier*, Y. L i u Department of Physics and Astronomy, The University of Glasgow, Glasgow, Scotland G12 8QQ, UK
The quantitative evaluation of recording-head fields is an important aspect of the goal of increased data-storage density for both hard disk and tape recording. Over the last few years, we have developed the method of electron beam tomography, originally introduced by Prof. Kubalek's group at the University of D u i s b u r g [J.B. Elsbrock, W. Schroder, E. Kubalek, IEEE Trans. Magn. 21 (1985) 1337] and applied it to determine the 3D field distributions for advanced thin-film and tape-recording heads. The basis of the method is that we require as input data for the tomographic reconstruction algorithms a number of different 'views' of the magnetic field of the head and this is achieved using the method of differential phase contrast (DPC) imaging in a 200 kV scanning transmission electron microscope [R.P. Ferrier et al., J. Magn. Magn. Mater. 149 (1995) 387]. DPC imaging provides us with signals which are related to orthogonal components of the magnetic induction of the field normal to and integrated along the electron trajectory. The pair of signals are determined along line scans parallel to the ABS as the head is rotated progressively through small angular increments about an axis normal to the optic axis and the ABS. Typically, the angular increment used is A0 = 5° and the total angular range is (180-A0) °. We have available two different reconstruction algorithms; the first is based on back-projection of real-space data and the second on the iterative solution of a set of linear equations. From knowledge of the experimental conditions the field determination may be put on an absolute basis. The wider application of tomographic methods to the study of thin-film heads has been hindered by the experimental difficulty of maintaining the ABS accurately parallel to the optic axis as the head is rotated to collect the full-data set. We have shown that this difficulty can be overcome by deliberately misaligning the head and mounting it so that the ABS is at a small angle to the optic axis; we show that the resulting loss of information relevant to head performance is minimal. Results are presented for IBM OEM heads, where the field-profiles indicate that micromagnetic effects may be present; clearly, this is of great interest because of the inability of current head modeling in this respect. The study of prototype tape heads has also been carried out in collaboration with Philips and Exabyte. These types of head present their own experimental difficulties, which will be discussed briefly, but successful head reconstructions have been achieved and these will be presented.
* Corresponding author. Fax: + 44 41 334 9029; e-mail: [email protected].
0304-8853/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 5 9 1-X
112
R.P. Ferrier, E Liu / Journal of Magnetism and Magnetic Materials 175 (1997) l l l
112
Without recourse to full tomographic reconstruction, which involves substantial image and data processing and is relatively time consuming, a great deal of valuable information can be obtained from careful study of the DPC line-scan data. The use of these to investigate the onset of head saturation in both tape and thin-film heads will be discussed and also their use in the identification and characterisation of stray-flux production from sites away from the pole-gap region will be described.