![]() In addition to these standard elements of a commercial microscope, the static tester contains a laser diode, an electromagnet, a piezo-driven x– y stage, a hot plate and a differential detector. This light then passes through a crossed analyzer to have the maximum image contrast and read by a TV camera, which is connected to a computer via a frame-grabber. The change in the orientation of the polarization vector in the reflected light depends upon the local state of magnetization. The same microscope objective collects the light reflected from the sample. Here collimated output of a white light source is polarized and then focused on the sample using a microscope objective. ![]() The diagram of a modified polarization microscope or “static tester”, used for this purpose is shown in fig. ![]() The MO Kerr effect, which is used for the readout, also enables 2-D mapping of the variation in the state of magnetization in MO films. It also has been utilized in phase change media to study the crystalline marks on amorphous surfaces (or vice versa) by generating a reflectivity map of a section of surface area. Polarized-light optical microscopy has been used for studying the structure, dimension, jaggedness (or fractal dimension), nucleation, growth and collapse of magnetic domains in MO media ( Takahashi, Niihara and Ohta ). Observing the magnetic domains and structure in MO films constitutes a useful approach to media characterization. At this point, one has lost control of shaping the thermal environment for thermomagnetic writing, and the viability of a recording process based on impressed thermal gradients becomes questionable. Eventually, τ becomes shorter than the shortest thermal characteristic time of the recording medium, regardless of the aggressiveness of the film thermal design or the writing strategy. But increasing the linear speed of recording combines with the higher linear bit density to shorten the bit transit time to τ∼ L bit/ v. The resolution limitations when using an optical stylus whose lateral extent is W∼λ/ NA (wavelength/numerical aperture) are well known and obvious. ![]() Notice that the former strategy increases the relative linear speed of the write/read beam and the storage medium, while the latter requires improved along-track writing and reading resolution. Data throughput rates for rotating memory products are driven higher by increasing the disk rotation rate or increasing the linear bit density along the track, or both. The incident light is totally absorbed in the thick magnetic layers, and the resultant heat will diffuse laterally with diminished control from the more distant underlying heat sink.Īnother inevitable trend for high-performance MO storage media will be the necessity to increase the recording and playback rate. Consequently, the effectiveness of a design strategy utilizing a heat-sinking layer at the base of the film stack is significantly compromised. The total thickness of the metallic magnetic layers in these designs (∼50–100 nm) is much greater than that of the simple, single-layer structure illustrated in Fig. Examples of these design structures include light-intensity modulated direct overwrite (LIM-DOW), magnetically induced super-resolution (MSR), and magnetic amplification MO system (MAMMOS). In these cases, there typically are two or more magnetic layers with thermally controlled magnetic coupling to each other. McDaniel, in Encyclopedia of Materials: Science and Technology, 2001 3 Issues in Advanced MO Film Designs and Limits of Thermomagnetic WritingĪdvanced MO film designs for the attainment of higher performance or areal recording density usually have more complex magnetic film structures than that shown in Fig.
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