Na Helian

A scanning laser microscope system to observe static and dynamic magnetic domain behaviour

Scanning laser microscopes (SLMs) have been used to characterize the magnetic properties of materials for some time. The first SLM built was a purely static system capable of imaging magnetic domains. Dynamic capability was introduced with the development of the R-Theta microscope. However, this microscope utilizes a rotating drive. A scanning laser microscope has been designed to observe the dynamic behavior of domain switching during the thermomagnetic write process and the subsequent magnetization state (domain orientation) in stationary media, without the requirement for a rotating drive. It may also be used to write to the magneto-optic (MO) disk material thermomagnetically prior to imaging. Images are derived from the longitudinal and polar magneto-optic Kerr effects. In this paper, the different configurations for imaging are described and some initial images are presented.

Lowering aspect ratio of patterned islands to achieve ultrahigh storage densities

Patterned islands with high aspect ratio are easier to form single domain state due to the shape anisotropy. However, simply increasing the aspect ratio would not be an ideal way in a single-bit-per-island recording system because achieving ultrahigh storage densities and high data transfer rate will rely on being able to make narrower elements, with a lower aspect ratio, as close together as possible. In this work, it is found that a magnetocrystalline anisotropy down track oriented medium with narrow anisotropy angular distribution is preferred for patterned polycrystalline cobalt islands to form a uniform single domain demagnetized state with smaller aspect ratio than one with broad anisotropy angular distribution.

Scanning laser techniques for dynamic thermo-magnetic recording onto stationary media

Abstract Scanning laser microscopes (SLMs) have been used to characterise the magnetic properties of materials for some time (J. Magn. Magn. Mater. 95(1) (1991); IEEE Trans. Magn. 31(6 Pt. 1) (1995)). An SLM has been designed to facilitate a number of operating modes: both for writing and reading magneto-optical data. The current SLM is capable of thermo-magnetically recording bits onto magneto-optical thin films. Unlike previous SLMs, the current instrument has been designed to write bits both statically and dynamically onto stationary media. It will be used to write to magneto-optic (MO) disk material thermo-magnetically prior to imaging. Images may be derived from the longitudinal and polar magneto-optic Kerr effects, which are wavelength dependent, using the appropriate laser wavelength. In this paper the two configurations for dynamic recording are described.

Versatile optical system for static and dynamic thermomagnetic recording using a scanning laser microscope

Scanning Laser Microscopes (SLM) have been used to characterise the magnetic domain properties of various magnetic and magneto-optical materials. The SLM in our laboratory has been designed to enable both static and dynamic read-write operations to be performed on stationary media. In a conventional (static) SLM, data bits are recorded thermo-magnetically by focusing a pulse of laser light onto the sample surface. If the laser beam has a Gaussian intensity distribution (TEM00) then so will the focused laser spot. The resultant temperature profile will largely mirror the intensity distribution of the focused spot, and in the region where the temperature is sufficiently high for switching to occur, in the presence of bias field, a circular data bit will be recorded. However, in a real magneto-optical drive the bits are written onto non-stationary media, and the resultant bit will be non-circular. A versatile optical system has been developed to facilitate both recording and imaging of data bits. To simulate the action of a Magneto-Optical drive, the laser is pulsed via an Acousto-Optic Modulator, whilst being scanned across the sample using a galvanometer mounted mirror, thus imitating a storage medium rotating above a MO head with high relative velocity between the beam and medium. Static recording is simply achieved by disabling the galvanometer scan mirror. Polar magneto-optic Kerr effect images are acquired using multiple-segment photo-detectors for diffraction-limited scanned spot detection, with either specimen scanning for highest resolution or beam scanning for near real-time image acquisition. Results will be presented to illustrate the systems capabilities.

Current-modulating magnetic force microscope probe

A new current-modulating probe for the magnetic force microscope (MFM) is proposed in this article. The magnetic field, which will be used to interact with a magnetic specimen’s stray field, is induced on the sharp tip of the conical magnetic core surrounded by a microfabricated single turn conductive coil. The reciprocity principle is used to obtain the force acting on the probe due to the specimen’s stray field when scanned over a magnetic specimen. The magnetic field intensity is adjustable by control of the applied current. Images of specimens have been modeled using this probe. The suitability to different specimens is seen to be the biggest advantage of this scheme over the conventional probe designs.