Gengqi Lin

Investigations of LRE-HRE-TM thin films for hybrid recording

Light rare earth-heavy rare earth-transition metal (LRE-HRE-TM) thin films are a kind of important recording media. A lot of researches have been carried out on the LRE-HRE-TM thin films to improve its properties for data storage application and fruitful results have been achieved. This report gives a glance on the evolution of the research on LRE-HRE-TM recording media. At the same time, combined with the hybrid recording technology, some experimental results obtained on LRE-HRE-TM recording media are discussed, which suggest the promising prospect of the LRE-HRE-TM media in hybrid recording application.

Advanced hybrid recording media

Combining the advantages of hard-disk magnetic recording and magneto-optical recording, hybrid recording is regarded as promising candidate for extremely-high density recording technology beyond Tera bits/in2. To obtain such high areal density, hybrid recording media are required to have high coercivity and large remanent magnetization at room temperature, the desired temperature dependence of coercivity and magnetization, as well as very short thermal response time. Currently, the researches on the hybrid recording media mainly involve the magnetic hard-disk polycrystalline recording media and the magneto-optical amorphous media. This report presents the latest progresses in the researches on these two kinds of media for hybrid recording.

Optical and Electric and Structural Properties of Ti1-xAlxN Thin Films

A sequence of Ti1-xAlxN films has been prepared by rf reactive magnetron sputtering. The optical and electric properties versus aluminum content x have been studied. Values suitable for magneto-optic protective layers have been achieved in Ti1-xAlxN thin films with aluminum content x > 0.75. X-ray diffraction results show that Ti1-xAlxN thin films in this study are a bcc structure up to x = 0.75, further increase in the aluminum content gives a wurtzite structure. All of the results show that the optical and electric properties of Ti1-xAlxN films might be related to the crystal structure.

Preparation and properties of (Sm,Nd)(Tb,Dy)Co thin film with perpendicular anisotropy

The (Sm,Nd)(Tb,Dy)Co thin Film had been prepared with spf-430H r.f.-magnetron sputtering system. The effects of heavy rare earth Tb, Dy substituted by light rare earth Sm, Nd on the magnetic and magneto-optical properties have been investigated. With the increasing of light rare earth Sm, Nd composition, the saturation magnetization Ms, the reflectivity R and the Kerr rotation angle θk are increased, while the coercivity (Hc) is decreased distinctly. This can be explained with the ferri-magnetic structure of RE-TM alloy. Mr/Hc Ratio is increased with the increasing of Sm composition in SmTbCo and SmDyCo. The influence of composition and sputtering conditions on perpendicular anisotropy films are reported in detail.

Magnetic and magneto-optic properties of TbCo/Cr thin films

The magnetic and magneto-optic properties of TbCo/Cr thin films were studied. A comparison of the MO properties was made between TbCo thin films with and without Cr underlayer. It was found that Cr underlayer helps to increase the Kerr rotation angle and to enhance the coercivities of TbCo thin films. The effects of the thickness of Cr underlayer and the gas pressure during Cr underlayer preparation on the magnetic and magneto-optic properties of TbCo layers were investigated, as well as the temperature dependence of these properties of TbCo/Cr thin films.

Analysis of fatigue characteristic of sm-substituted DyFeCo magneto-optical films

The fatigue characteristic of the amorphous Sm-substituted DyFeCo magneto-optical alloy films fabricated by R.F. magnetron sputtering method were investigated by accelerated pulse training method under the condition of magnetic field modulation plus laser pulse irradiation. The evaluation of fatigue characteristic is determined from the static magneto-optical signal readout level after several writing/erasing repetitions compared with initial level. The experimental dependence of fatigue characteristics is in good agreement with the model based on the JMA equation. Furthermore, the Avrami factor can be derived from the model. Experimental results show that it is very effective in studying the writing/erasing ability of magneto-optical films employed the method of combined the accelerated pulse training with the JMA equation and Sm-substituted HRE-TM alloys can act as a practical medium for MO storage at short wavelength.

Temperature dependence of LRE-HRE-TM thin films

Temperature dependence of the properties of RE-TM thin films is very important for MO recording. In this paper, we studied the temperature dependence of the magnetic and magneto-optical properties of the amorphous LRE-HRE-TM single layer thin films and LRE-HRE-TM/HRE-TM couple-bilayered thin films. For LRE-HRE-TM single layer thin films, the temperature dependence of the magnetization was investigated by using the mean field theory. The experimental and theoretical results matched very well. With the LRE substitution in HRE-TM thin film, the compensation temperature Tcomp decreased and the curie temperature Tc remained unchanged. Kerr rotation angle became larger and the saturation magnetization Ms at room temperature increased. For LRE-HRE-TM/HRE-TM couple-bilayered thin films, comparisons of the temperature dependences of the coercivities and Kerr rotation angles were made between isolated sublayers and couple-bilayered thin film.

Sm substitution effects on the magnetic and magneto-optical properties of TbCo/Cr films

In order to meet the requirements of high saturation magnetization (Ms) and large coercivity (Hc) at room temperature for hybrid recording, the TbCo/Cr films with perpendicular anisotropy were prepared by an r.f. magnetron sputtering system without applying bias voltage. The influence of sputtering conditions and the effects of Sm substitution on the magnetic and magneto-optical properties of TbCo/Cr films were studied. It was found that although the Hc of TbCo/Cr could be optimized by choosing suitable sputtering parameters, but the partial Tb substituted by Sm will directly affect the magnitude of saturation magnetization Ms and the Kerr rotation angle 0k. This can be explained with the feeri-magnetical structure of RE-TM alloy. Under the optimized sputtering conditions, when the magnetic layer composition was (Sm0.343Tb0.657)31Co69, the Ms as high as 385emu/cm3 and the Hc as high as 4.7KOe at room temperature were obtained.