N.A.E. Heyes

Development of a scanning laser microscope for magneto-optic studies of thin magnetic films

Abstract A magneto-optic scanning laser microscope has been built which is capable of observing the magnetic domain structure present in materials which exhibit the Kerr (polar and longitudinal) and Faraday magneto-optical effects. The samples are not specially coated to improve the Kerr contrast, images being formed of the domain structures in the “as produced” samples. The instrument is also capable of observing nonmagnetic contrast. In addition the microscope may be used, together with a high-power Ar ion laser, as a thermo-magneto-optic bit writer

Observations of magneto‐optic phase contrast using a scanning laser microscope

A scanning laser microscope (SLM) has been built which is capable of observing magnetic structure via ‘‘conventional’’ Kerr imaging techniques and a ‘‘novel’’ magneto‐optic phase contrast approach. This latter contrast mode highlights magnetic transitions, rather than domains themselves. In this paper we present results of observations in TbFeCo samples using this phase contrast technique and assess its possible application as a read‐out mechanism for magneto‐optic recording systems.

Scanning laser microscope studies of the overwrite characteristics of TbFeCo films using magnetic field modulation

In the search for a directly overwritable magneto‐optic recording system, that based upon the magnetic field modulation method looks quite favorable. This approach also enables submicron domains to be written, so increasing attainable storage densities. Here we report on the results of such field modulation studies performed in situ using our magneto‐optical scanning laser microscope (SLM). Bit patterns were recorded in TbFeCo films by continuous laser irradiation coupled with the application of an alternating magnetic field supplied by a small, purpose built electromagnet having a peak field of approximately 4 kOe. The recorded domain structures were then imaged using the SLM in its polar Kerr mode. Recorded patterns were overwritten and the resulting bit patterns observed.

Observations of magnetisation distribution in narrow permalloy strips

Abstract We have used a scanning laser microscope which employs a novel detection tochnique to allow information on magnetisation distributions in the plane of the sample to be obtained. Results are presented which show that the magnetisation distributions found across the strips differ from those computed from the theory.

A highly versatile scanning laser microscope for magneto-optic observation of micromagnetic structure

Abstract A scanning laser microscope has been developed which produces high quality magnetisation images from samples using either the Faraday or Kerr magneto-optical effects. The microscope can also image non-magnetic samples. The design of the instrument is discussed and images of the magnetic structure in thin film specimens are presented.

A short wavelength R-/spl theta/ scanning laser microscope and optical disc tester for the characterization of optical recording media

The design and applications of a novel, short wavelength, combined R-/spl theta/ scanning laser microscope (SLM) and optical disc tester that is used for the imaging of recorded bit structures and the characterization of optical recording media is described. The instrument is optimised for magneto-optical recording applications and provides images with sub-micron resolution. Imaging is achieved by focusing the light from an argon-ion laser (514 nm or 488 nm wavelength) to a diffraction limited spot on the surface of a rotating sample to generate the line scan, whilst moving the objective lens slowly in the radial direction to generate the frame scan.

Magnetization distributions in thin film Permalloy strips

Thin film Permalloy strips are used extensively for magnetoresistive sensors both in magnetometry and magnetic recording. A determination of magnetization distributions is vital to allow optimization of sensor performance. Results from a previously described scanning laser microscope (SLM) unambiguously determine magnetization distributions to submicron resolution. Operating the SLM in a mode sensitive to magnetization angles about the long axis of the strip shows typical closure domains. If the mode is sensitive to fluctuations about the strip short axis then light and dark bands are observed. These results indicate that the magnetization is not parallel with the strip edges within the domains as normally considered for closure domains. The SLM images are compared with results from a previously described numerical micromagnetic model. Results from the model compare well with those from the SLM, confirming the ability of the model to reliably predict domain activity in Permalloy strips. Results are shown ...

Depth-discrimination-based focus error detection scheme for optical storage applications

A novel, differential focus error detection scheme for use in optical recording applications is described. The technique is based on the depth-discrimination property of confocal optical systems. A simple theoretical treatment is used to predict the form of the focus error signal, which is also investigated experimentally using a scanning optical microscope. The focus error response is found to exhibit a more than adequate lock-on range and gain, and is expected to be less sensitive to tracking feedthrough and other forms of cross-talk.

Short wavelength recording studies in amorphous TbFeCo films for magneto-optic recording applications

Abstract Recording studies on TbFeCo films have been performed using an argon ion laser at 514.5 nm and a scanning laser microscope. The resulting bit size and shape has been correlated both with material properties and system performance.

Characterization of the performance of magneto-optic recording media using a scanning laser microscope

A scanning laser microscope (SLM) capable of performing a wide range of in-situ recording tests on magneto-optic storage media is described, and the results of such tests presented.