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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Time-resolved observation of Barkhausen avalanche in Co thin films using magneto-optical microscope magnetometer

Dong-Hyun Kim, Sug-Bong Choe, and Sung-Chul Shin

J. Appl. Phys. 93, 6564 (2003); http://dx.doi.org/10.1063/1.1557350 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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We develop an experimental technique for direct, full-field, time-resolved observation of the Barkhausen avalanche in a two-dimensional thin-film system, using a magneto-optical microscope magnetometer (MOMM). Real-time visualization capability of the MOMM enables us to microscopically observe all the details of the Barkhausen avalanche in Co thin films, which is not feasible using other indirect experimental techniques adopted so far. We find that there exist fluctuating flexible domain walls deformed by defects and that, interestingly enough, the domain wall exhibits still-detectable fluctuation even around a strong linear defect as well as a strong point-like defect, from which we conclude that a critical avalanche continues to exist even in strong pinning cases. © 2003 American Institute of Physics.
Show PACS
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects

Variation of the magnetic domain structure with reversal field (invited)

R. C. Woodward, A. M. Lance, R. Street, and R. L. Stamps

J. Appl. Phys. 93, 6567 (2003); http://dx.doi.org/10.1063/1.1557654 (5 pages) | Cited 15 times

Online Publication Date: 9 May 2003

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A rate dependence of the magnetic domain structure has been observed in a Pt/Co multilayer. The form of the domain structure as a function of the rate of change of magnetization was studied using nanosecond pulsed magnetic fields. At low fields the magnetization pattern consists of a dendritic like growth of the domains. As the magnitude of the pulse field is increased the patterns change to a more circular structure with smooth boundaries. The change in structure can be quantified and is discussed in terms of a field dependence where different behaviors can be clearly identified. The structure observed results from a narrowing of the distribution of energy barriers to reversal as the field is increased. © 2003 American Institute of Physics.
Show PACS
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
68.37.Rt Magnetic force microscopy (MFM)

External field effects on the resonant frequency of magnetically capped oscillators for magnetic resonance force microscopy

Casey W. Miller, Utkur M. Mirsaidov, Troy C. Messina, Yong J. Lee, and John T. Markert

J. Appl. Phys. 93, 6572 (2003); http://dx.doi.org/10.1063/1.1557351 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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We study the resonant frequency shift of CoPt-capped single-crystal-silicon micro-oscillators when a magnetic field is applied perpendicular to the magnetic film, as required for application to nuclear magnetic resonance force microscopy. The oscillator resonant frequencies show two distinct regimes of behavior. At low fields, when the magnetic moment is nearly perpendicular to the external field, the frequency decreases sharply with field, while at high fields, when the moment and field are nearly aligned, the frequency increases. We present models that accurately describe both behaviors. The transition point between these two regimes scales with the volume of the micromagnets. © 2003 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities

Evidence of a topological antiferromagnetic order on ultrathin Cr(001) film surface studied by spin-polarized scanning tunneling spectroscopy

T. Kawagoe, Y. Suzuki, M. Bode, and K. Koike

J. Appl. Phys. 93, 6575 (2003); http://dx.doi.org/10.1063/1.1557352 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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Imaging of the surface magnetic structure of Cr(001) films epitaxially grown on Au(001) film was performed by using spin-polarized scanning tunneling spectroscopy and Fe-coated W tips. It is shown that two-step growth of a 4-nm-thick Cr layer having two different growth temperatures results in a chemically clean surface and makes it possible to observe distinct spin contrast. The spatially resolved maps of dI/dV signals taken at room temperature indicated that the topological antiferromagnetic order on the thin Cr(001) film surface that is subject to high-density steps and screw dislocations. © 2003 American Institute of Physics.
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75.70.Rf Surface magnetism
75.50.Ee Antiferromagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.A- Nucleation and growth
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

High-speed massive imaging of hard disk data by using the spin-stand imaging technique

C. Tse, I. D. Mayergoyz, D. I. Mircea, and C. Krafft

J. Appl. Phys. 93, 6578 (2003); http://dx.doi.org/10.1063/1.1557353 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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High-speed massive imaging of hard disk data by using the spin-stand imaging technique [I. D. Mayergoyz, C. Serpico, C. Krafft, and C. Tse, J. Appl. Phys. 87, 6824 (2000) and I. D. Mayergoyz, C. Tse, C. Krafft, and R. D. Gomez, J. Appl. Phys. 89, 6772 (2001)] is reported. In order to obtain these large-scale images of hard disk data, disks from commercial hard drives were scanned by a giant magnetoresistive head in the along- and cross-track directions. A special method of triggering has been devised to capture the data nondestructively. Challenges related to the eccentricity of the disk and the instability of the trigger have also been addressed. By using this massive imaging technique, we were able to image disk data with track densities as high as 60 000 tracks per inch. With a specially designed automated algorithm, the developed technique can be programmed to image the drive data of the whole disk surface with high resolution and speed. © 2003 American Institute of Physics.
Show PACS
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
07.05.Hd Data acquisition: hardware and software

Scaling of head response function in spin-stand imaging

I. D. Mayergoyz, C. Tse, D. I. Mircea, and C. Krafft

J. Appl. Phys. 93, 6581 (2003); http://dx.doi.org/10.1063/1.1557655 (3 pages)

Online Publication Date: 9 May 2003

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Scaling of head response function in spin-stand imaging is proposed. This scaling is performed in order to improve the accuracy of the measured head response function. This response function is measured by imaging a small spot of magnetic charges formed as a result of dc-trimming of isolated transitions. The theoretical justification for the scaling is the “nearly” self-similar nature of the measured response function with respect to the cross-track dimension of the charged spot. This scaling technique has been tested experimentally. It is demonstrated that the scaling of head response function allows one to reconstruct magnetization images of overwritten data that cannot be discerned otherwise. © 2003 American Institute of Physics.
Show PACS
75.50.Ss Magnetic recording materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
85.75.Bb Magnetic memory using giant magnetoresistance
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