The linear thermal expansion, AC susceptibility and magnetostriction have been measured on a single crystal of HoA12. Our results clearly show two phase transitions associated, respectively, with establishment of magnetic order and with spontaneous spin reorientation. The critical exponent ySR of the susceptibility for l-3 TSR has been determined. From magnetostriction measurements along the major symmetry directions of the crystal, we have obtained the possible deformation modes compatible with the point symmetry of the cubic crystal structure. A complete study of the magnetoelastic behaviour has allowed us to determine the reduced magnetoelastic coupling coefficients M : / C y , M i / C ' , M f / C " (I = 4,6)and D"/C".Themodelusedisbasedonasingle-ionorigin for the crystal electric field interaction of the rare-earth ion, and we have taken into account the spontaneous reorientation of the magnetic moment in the molecular field, which represents the exchange interaction.

We have developed a super-resolution read-only memory (ROM) disc with a high readout stability using a zinc oxide (ZnO) thin film. Applying the reversible and repeatable change in the optical constants of ZnO induced by heat, we can successfully confirm super-resolution effects that can read out a small mark beyond the optical diffraction limit. By realizing this characteristic in a ROM disc, we obtained a linear bit density twofold higher than that of a conventional disc in the blue-laser optical system. To clarify the origin of ZnO super resolution, we performed two types of test: a test to compare ZnO super-resolution characteristics using blue- and red-laser optical systems, and a test to determine the relationship between the absorption edges of semiconductor films with various energy band gaps and readout laser wavelength.

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Energy-gap-induced super-resolution (EG-SR) technology has been developed for high-density optical discs with a high readout stability using a zinc oxide (ZnO) thin film. ZnO film indicated a thermal change in optical properties. By applying these effects to a read-only-memory (ROM) disc, we obtained a linear bit density twofold that of conventional ROM discs in our experimental optical pickup system with a 404-nm-wavelength laser and a 0.85-numerical-aperture (NA) objective lens. In this study, we report an optical disc technology that enables super-resolution readout of data pits in a dual-layer structure by employing a transparent ZnO super-resolution functional film.

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